Glossary of technical terms for the use of metallurgical engineers Terms starting with alphabet ‘H’
Glossary of technical terms for the use of metallurgical engineers
Terms starting with alphabet ‘H’
H-13 tool steel – It is a chromium-molybdenum-vanadium hot-work tool steel, widely considered the ‘workhorse’ of the tooling industry. It is defined by high toughness, excellent resistance to thermal fatigue (heat checking), and superior wear resistance. H-13 tool steel is predominantly used for die casting, forging, and extrusion dies.
Haar functions – These are an orthogonal family of switched rectangular waveforms, defined on the interval (0,1). They consist of values of +/- over specific intervals and zero elsewhere.
Haar wavelet – It is defined as a set of square wave functions that take values of +/-1 over specific intervals and zero elsewhere, characterized by a level of resolution and a translation parameter. It is used in different mathematical applications, particularly for solving differential equations, because of its simplicity and computational efficiency.
Haber-Bosch process – It is the main industrial method for producing ammonia (NH3) by reacting atmospheric nitrogen (N2) and hydrogen (H2) over an iron catalyst at high temperatures (400 deg C t0 650 deg C) and high pressures (20 mega-pascals to 40 mega-pascals). it is necessary for fertilizer production. Reaction taking place in the process is N2 + 3H2 = 2NH3.
Habitat – It means the natural home of a living organism. The three components of wildlife habitat are food, water, and shelter.
Habit plane – It is the specific, often irrational, crystallographic plane that acts as the interface between a parent phase (e.g., austenite) and a newly formed product phase (e.g., martensite or precipitate). It is characterized as a low-energy, invariant plane which remains unrotated and undistorted during rapid, diffusion-less transformation. It is the plane or system of planes of a crystalline phase along which some phenomenon, such as twinning or transformation, occurs.
Habit plane indices – These indices represent the {hkl} Miller indices of the specific, frequently irrational, crystallographic plane separating a parent phase (e.g., austenite) from a new product phase (e.g., martensite). It is the plane of minimum lattice mismatch that remains undistorted and unrotated during transformation. The habit plane is the interface along which a new phase (frequently a thin, plate-like, or lath structure) grows from the parent phase. It is important for determining the shape memory effect, deformation, and micro-structure evolution in alloys.
Hackle (glassy materials, ceramics) – It is a line on a crack surface, running parallel to the local direction of cracking, separating parallel but non-coplanar portions of the crack surface.
Hackle marks (ceramics, glassy materials) – These are fine ridges on the fracture surface of a glass, parallel to the direction of propagation of the fracture.
Haddon matrix – It is a 3×4 framework used in injury prevention to analyze accidents by examining the interaction between three temporal phases (pre-event, event, post-event) and four contributing factors (human / host, agent / vector, physical environment, and social environment). It is mainly used to brainstorm, plan, and evaluate safety interventions.
Hadfield manganese steel – It is a high alloy steel which contains 12 % to 14 % manganese and 1 % carbon. It is austenitic at all temperatures and hence non-magnetic. Hadfield had done a series of test with the addition of ferro-manganese containing 80 % manganese and 7 % carbon to de-carbonized iron. Increasing manganese and carbon contents led to increasing brittleness up to 7.5 % manganese. At manganese contents above 10 %, however, the steel became remarkably tough. The toughness increased by heating the steel to 1,000 deg C followed by water quenching, a treatment which would render carbon steel very brittle. This alloy steel which was introduced commercially contained 1.2 % carbon and 12 % manganese in a 1 to 10 ratio. Hadfield manganese steel is unique in that it shows resistance to impact, high toughness, high ductility, high work hardening ability, excellent wear resistance, and slow crack propagation rates, in comparison to other potentially competitive materials. The steel has a unique property in that when the surface is abraded or deformed, it greatly increases surface hardness while retaining a tough core. The steel has the ability to harden in-depth in service as well as by induced means. It is also non-magnetic and can be work-hardened during service or can be surface-hardened to as high as 500 HB (Brinell hardness) by mechanical or explosive means prior to service. Because of these properties, Hadfield manganese steel gained rapid acceptance as a useful engineering material.
Hafnium (Hf) – It is a lustrous, silvery-gray, ductile refractory transition metal (atomic number 72) known for its excellent corrosion resistance, high melting point (2,233 deg C), and extreme chemical similarity to zirconium. Mainly used in nuclear control rods, superalloys, and electronics, it is frequently found in zirconium minerals and is necessary for high-temperature / specialized applications. Hafnium has outstanding corrosion resistance and good mechanical properties. It is added to specialty alloys for use in jet engine parts and as control rod material in nuclear reactors.
Hagen Poiseuille equation – It is a fundamental equation in fluid mechanics which calculates the pressure drop of a Newtonian fluid flowing through a straight, circular channel under steady state, laminar flow conditions. It is applicable only for laminar flow in circular pipes with a Reynolds number less than 2,000 and does not consider channel roughness.
Hagen–Poiseuille law – It is the relationship which describes the flow rate (Q) of a fluid in laminar flow through smooth-walled, straight, circular pipes, expressed as a function of the pressure gradient (delta P), pipe radius (r), pipe length (L), and fluid viscosity (mu).
Haigh diagram – It is frequently referred to as a Haigh-Goodman diagram or constant life diagram. It is a graphical tool used to represent the fatigue behaviour of a material by plotting the alternating stress amplitude on the vertical axis against the mean stress on the horizontal axis. It is used to define the safe operating limits for components subjected to cyclic loading (fatigue), showing how the mean stress influences the fatigue strength (fatigue endurance limit).
Hail – It is a form of solid precipitation which consists of balls or irregular lumps of ice, which are individually called hail stones. Hail stones on earth consist mostly of water ice and measure between 5 millimeters and 150 millimeters in diameter, with the larger stones coming from severe thunderstorms.
Hair, slitter – It is the minute hairlike sliver along edge(s) because of the shearing or slitting operation.
Hair grease – It is a grease which contains horse hair or wool fibre.
Hairline cracks – These are short, discontinuous internal cracks in ferrous metals attributed to stresses produced by localized transformation and hydrogen-solubility effects during cooling after hot working. In fracture surfaces, hairline cracks appear as bright, silvery areas with a coarse texture. In deep acid-etched transverse sections, they appear as discontinuities which are normally in the midway to centre location of the section. In refractories, a hairline crack is a fine crack which is visible on the surface of a brick or a block whose length can be measured and whose width is less than or equal to 0.2 millimeters.
Hairline craze – It consists of multiple fine surface separation cracks in composites which exceed 6 millimeters in length and do not penetrate in depth the equivalent of a full ply of reinforcement.
Hajidavalloo – It refers to his research on energy and exergy analysis of electric arc furnaces (EAF).
Half-cell – It is an electrode immersed in a suitable electrolyte, designed for measurements of electrode potential.
Half hard – It is a temper of non-ferrous alloys and some ferrous alloys characterized by tensile strength around mid-way between those of dead soft and full hard tempers.
Half journal bearing – It is a journal bearing extending 180-degee around a journal.
Half-life – It is the time needed for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear metallurgy to describe how quickly unstable atoms undergo radio-active decay or how long stable atoms survive, i.e., It is the time which it takes for half of the atoms in a radio-active element to decay. The term is also used more generally to characterize any type of exponential (or, rarely, non-exponential) decay.
Half-mask respirator – It is a type of air-purifying respirator which fits over the nose and mouth but does not cover the entire face. It is available in different performance classifications and is designed to filter out harmful gases, vapours, and particulates from the air.
Half model – It is defined as a testing configuration mounted on a wind tunnel sidewall or floor, which eliminates the need for a separate support system and involves considerations for tunnel boundary layer control. It can be spaced from the wall to account for boundary layer displacement thickness, allowing for accurate force and moment measurements.
Half power bandwidth – It is also called 3-dB (decibel) bandwidth. It is defined as the range of frequencies where the magnitude spectrum falls no lower than half of the peak value, resulting in a bandwidth calculated as B = f2 – f1, where f1 and f2 are the frequencies at which the signal power is 3 dB lower than the peak signal power. It defines the operating range of filters and amplifiers, where amplitude corresponds to 1/root 2 (around 0.707) of its maximum.
Half-power frequencies (f1, f2) – These are the two points in a system’s frequency response, frequently called -3dB or cutoff frequencies, where the power output drops to half (1/2) of its maximum (resonant) value. At these points, current or voltage amplitude drops to 1/root 2 (around 0.707) of the peak, defining the system’s bandwidth.
Half sectional view – In technical drawings, it shows both the internal and external features of a symmetrical object by cutting away only a quarter of the object, revealing the interior of one half while retaining the exterior of the other. Half sections are mainly used for symmetrical objects, where the object is the same on both sides of a central plane.
Half-warm mix asphalt – It is an eco-friendly pavement material produced and compacted at temperatures between 60 deg C and 100 deg C, typically using bitumen emulsions or foaming technology to lower energy consumption. It acts as a sustainable intermediate between cold and hot mix asphalt, frequently incorporating high percentages of reclaimed asphalt pavement (RAP).
Half-wavelength (lambda/2) – It refers to a distance equal to half the length of one full cycle of a wave (crest to trough), normally used to define resonant antenna lengths, transmission line lengths, or structural buckling modes. It represents a 180-degree phase shift, essential for calculating maximum power transfer or structural stability.
half-wave rectifier – It is an electrical circuit which converts alternating current (AC) into pulsating direct current (DC) by allowing only one half-cycle (either positive or negative) of the input alternating current voltage to pass while blocking the other, using a single diode. It is the simplest rectification method, typically used in low-power applications because of its low efficiency (around 40.5 %) and high ripple.
Half-width values diagram – In X-ray diffraction (XRD) and material characterization, It normally refers to a plot of the ‘full width at half maximum’ (FWHM) of diffraction peaks against a metallurgical parameter, such as deformation, microhardness, or heat treatment time. It is a diagnostic tool used to analyze the internal state of a metal, such as lattice strain, crystallite size, or residual stresses, based on the broadening of spectral lines.
Halide environments – These environments refer to chemical conditions, processes, or atmospheres which contain halogens (fluorine, chlorine, bromine, iodine) and their corresponding halide ions (F⁻, Cl⁻, Br⁻, I⁻) or metal halides (e.g., TiCl4, MgCl2, NaCl). These environments are used in extractive metallurgy to extract, refine, or purify metals, particularly refractory metals, by converting their ores into metal halides, which are frequently more easily volatilized or reduced than their oxide counterparts.
Halides – These are inorganic binary compounds formed by the combination of a metal with a halogen (fluorine, chlorine, bromine, or iodine). These compounds, such as sodium chloride (NaCl) or fluorite (CaF2), serve as vital intermediate products for extracting pure metals through electrolysis or reducing metal halides with more reactive metals.
Halite – It is the naturally occurring mineral form of sodium chloride (NaCl), normally known as rock salt, featuring a cubic crystal structure. It is mainly used as a flux in refining metals, in electrolysis to produce sodium and chlorine gas, and in heat-treating salt baths. It is soft (2.5 on Mohs scale), highly soluble, and is formed through evaporation from saline water. It has an fcc (face-centered cubic) Bravais lattice, with alternating sodium (Na+) and chlorine (Cl-) ions. It possesses perfect cubic cleavage (breaks at 90-degree angles).
Hall effect – It is the development of a transverse electric field in a current-carrying conductor placed in a magnetic field.
Hall Heroult process, smelting – It is the main process used for the production of aluminum metal whereby alumina is dissolved in a salt bath of molten cryolite and subject to an electrolysis process. It is frequently referred to as smelting. This process uses very large quantities of electricity. This process is named after two scientists who developed the process independently of each other at around the same time.
Halloysite nano-tubes – These are naturally occurring, tubular-structured clay minerals, formula Al2Si2 O5(OH)4.H20, composed of rolled-up alumino-silicate layers. In metallurgy, HNTs are used as low-cost reinforcement fillers in composites, high-temperature ceramic stabilizers, and as nano-porous carriers for catalysts or corrosion-inhibiting agents.
Hall paste process – It is a ball milling process for powder production in which a liquid hydrocarbon is used as a suspension medium.
Hall-Petch effect – It is also known as the Hall-Petch relationship. It describes how the grain size of a polycrystalline material affects its strength. It states that smaller grain sizes lead to increased yield strength (or hardness) in metals and alloys. This relationship is because of the grain boundaries acting as barriers to dislocation movement, a key mechanism in plastic deformation.
Hall-Petch relationship – It is a general relationship for metals which shows that the yield strength is linearly related to the reciprocal of the square root of the grain diameter.
Hall process – It is a commercial process for winning aluminum from alumina by electrolytic reduction of a fused bath of alumina dissolved in cryolite.
Hall thruster – It is a coaxial device which utilizes orthogonal electric and magnetic fields to ionize propellant gases, such as xenon, or krypton, and accelerate the resulting ions to produce thrust. The thruster operates by creating a cross-field discharge which leverages the Hall effect on plasma particle motion.
Halocarbons – Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine) resulting in the formation of organo-fluorine compounds, organo-chlorine compounds, organo-bromine compounds, and organo-iodine compounds. Chlorine halocarbons are the most common and are called organo-chlorides. Halocarbons are typically non-flammable and nonreactive though some halocarbons are broken down by ultraviolet radiation in the upper atmosphere and this process releases free halogen atoms that damage the ozone layer. Some halocarbons have also been implicated as greenhouse gases.
Halo effect – It is a cognitive bias where an overall positive impression of a person, brand, or product—based on one, frequently superficial, trait, influences observers to assume other positive, unrelated qualities. It is a mental shortcut, or heuristic, which can lead to unfair judgments and poor decision-making.
Halogens – These are group 17 elements, namely fluorine, chlorine, bromine, Iodine, astatine). Halogens are highly reactive non-metals used as agents to extract or refine metals by forming metal halides. They act as salt-formers, bonding with metals to create compounds utilized in processing, cleaning, and refining ores.
Halogenated acetic acids – They are carboxylic acids, such as chloro-acetic or trichloro-acetic acid, where hydrogen atoms on the methyl group of acetic acid are replaced by halogens (chlorine, bromine, iodine). These acids are used as intermediate agents in chemical processing or as agents for surface treatment / cleaning because of their high reactivity and acidity.
Halogenated aromatic hydrocarbons – These are aromatic compounds (e.g., benzene rings) with substituted halogen atoms (chlorine, fluorine, bromine) which frequently act as contaminants, hazardous byproducts of thermal processing, or, in specific contexts, as additives in lubricants or heat-transfer fluids. They are highly stable and pose environmental risks.
Halogenated hydrocarbons – These are also known as halocarbons. These are organic compounds where one or more hydrogen atoms have been replaced by halogen atoms (fluorine, chlorine, bromine, or iodine). Their breakdown in the stratosphere releases chlorine and bromine which takes part actively in the destruction of stratospheric ozone. The best-known group of halogenated hydro-carbons are chloro-fluoro-carbons.
Halogenation – It is a chemical process which introduces halogens, typically chlorine, fluorine, bromine, or iodine, into a metal or ore to form metal halides (salts). This technique is mainly used in the extraction, purification, or separation of metals, such as converting metal oxides into volatile halides for refining, particularly for reactive or rare metals like titanium, zirconium, or rare earth elements.
Halogen derivatives – These are compounds formed by replacing one or more hydrogen atoms in hydro-carbons with halogen atoms (fluorine, chlorine, bromine, and iodine). These compounds react with metals (like aluminium) to cause corrosion or are used in metal surface treatment processes.
Halon – It is sometimes being referred to as haloalkane, or halogenoalkane. It is a group of chemical compounds consisting of alkanes with linked halogens. Halons are mainly used as fire extinguishing agents, both in built-in systems and in portable fire extinguishers.
Halpin-Tsai model – It is a semi-empirical mathematical framework used to predict the effective elastic modulus (stiffness) of fibre-reinforced composites and nano-composites. It relates the composite’s overall stiffness to the fibre volume fraction, geometry (aspect ratio), and the constituent properties of the matrix and fibre. It acts as a bridge between simple rules of mixture and complex numerical micro-mechanics.
Hamaker constant – It is a material-specific coefficient which quantifies the strength of van der Waals forces between two interacting bodies (e.g., solid particles, surfaces) separated by a vacuum or medium. It merges atomic properties with material density to dictate interactions like adhesion, friction, coating adhesion, and flotation.
Hametag process – It is a ball milling method of powder production in which an inert gas atmosphere is used to prevent oxidation of the powder.
Hamiltonian – It is the foundational mathematical expression representing the total energy of a system, specifically the sum of its kinetic energy and potential energy. It is used to analyze the thermo-dynamic, structural, and kinetic properties of metals, alloys, and crystal structures.
Hamiltonian equations – These refer to the equations of motion derived from the Hamiltonian formulation of mechanics, which relate the generalized coordinates and their conjugate momenta. They are got through a Legendre transformation of the Lagrangian and express the dynamics of a system in terms of the Hamiltonian function, H(q, p, t).
Hamiltonian form – It refers to a mathematical reformulation of system dynamics (such as phase transformations, magnetization, or atomic motion) based on the Hamiltonian function H(q.p.t), which typically represents the total energy (kinetic + potential) of the system. Rather than using second-order Newton-type equations, the Hamiltonian form expresses the system’s evolution using first-order differential equations (Hamilton’s equations) acting on a 2n-dimensional phase space of generalized positions (q) and conjugate momenta (p): qi = dH/dpi, pi = -dH/dqi.
Hamiltonian formulation – It refers to a mathematical framework which describes the total energy (H) of a metallurgical system as a function of generalized coordinates (e.g., atomic positions, q) and their conjugate momenta (p). It is a powerful approach for analyzing, simulating, and predicting the dynamical and thermodynamic properties of materials.
Hamiltonian function (H) – It is a fundamental scalar function which represents the total energy of a system (the sum of kinetic energy ‘T’ and potential energy ‘V’) expressed in terms of generalized coordinates (q) and their conjugate momenta (p). While rooted in classical mechanics, it is heavily used in computational materials engineering and physical metallurgy to simulate atomic-level behaviours, phase transformations, and microstructure evolution.
Hamiltonian matrix (H) – It is a mathematical representation of the total energy (kinetic + potential) of a system of electrons and nuclei, derived from the Schrodinger equation. It describes electron energy levels, bonding, and interactions within a crystal lattice to predict atomic behaviour.
Hamiltonian mechanics – It is a reformulation of classical mechanics. It describes the motion of a system using the Hamiltonian function, which is frequently the total energy expressed in terms of generalized coordinates and momenta, rather than velocities. This approach provides a link between classical and quantum mechanics and has close ties to geometry. In Hamiltonian mechanics, the central concept is the Hamiltonian (H), which represents the total energy of the system. It is typically expressed as a function of generalized coordinates (q) and their corresponding momenta (p). Hamiltonian mechanics operates in a space called phase space, which has coordinates (q, p). This contrasts with Lagrangian mechanics, which uses coordinates (q) and velocities (v).
Hamilton’s equations of motion – These are a set of first-order differential equations which describe the evolution of a physical system in terms of generalized coordinates and momenta, rather than position and velocity. They are derived from the Hamiltonian, which represents the total energy of the system expressed as a function of coordinates and momenta. These equations are also known as canonical equations of motion and are a cornerstone of Hamiltonian mechanics.
Hamilton’s principle – It is frequently referred to as the principle of stationary action or the principle of least action. It is a foundational variational principle in classical mechanics, which also applies to advanced metallurgical modeling, such as phase transformations, solidification, and structural dynamics of materials. It states that the true trajectory of a physical system (e.g., a deforming lattice, a propagating crack, or a solidifying alloy) between two states at times ‘t1’ and ‘t2’ is the one which renders the action integral (S) stationary (normally a minimum).
Hammer – It is a machine which applies a sharp blow to the work area through the fall of a ram onto an anvil. The ram can be driven by gravity or power.
Hammer blow – In electric actuators, it is a lost motion mechanism to allow a motor to reach full speed before engaging the gear drive. It provides a higher efficiency for overcoming valve break torque, but it does not produce more torque than the nominal actuator rating.
Hammer crusher – It consists of a high-speed, normally horizontally shaft rotor turning inside a cylindrical casing. The crusher contains a certain number of hammers which are pinned to the rotor disk and the hammers are swinging to the edges because of centrifugal force. Feed is dropped to the crusher from the top of the casing and it is crushed between the casing and the hammers. After crushing the material falls through from the opening in the bottom.
Hammer forging – It is a type of forging in which the work is deformed by repeated blows.
Hammering – It is the working of metal sheet into a desired shape over a form or on a high-speed hammer and a similar anvil to produce the needed dishing or thinning.
Hammer peening – It is a cold-working metallurgical process which plastically deforms a metal surface through high-frequency, mechanical impacts from a ball-shaped hammer or tool. It induces compressive residual stresses, increases surface hardness, and improves fatigue resistance by preventing micro-crack initiation and propagation. It is frequently used for welding, treating fatigue-prone components, and improving material durability. The process stretches the surface of the metal, causing compressive residual stresses that counteract tensile stresses, reducing distortion and preventing fatigue failures.
Hammer welding – It means forge welding by hammering.
Hamming codes -These codes can detect one-bit and two-bit errors, or correct one-bit errors without detection of uncorrected errors.
Hamming distance – It is a metric mainly used in information theory, coding theory, and computer science to measure the dissimilarity between two strings of equal length. Hamming distance between two strings of equal length is the number of positions at which the corresponding symbols (characters, bits, or digits) are different. It quantifies the minimum number of substitutions needed to change one string into the other.
Hamming window – It is a window function applied to frames of speech signals to reduce the effects of leakage during the Fast Fourier Transform (FFT), characterized by the formula w(n) = 0.54 – 0.46 cos[(2 x pi x n)/(M-1)]) for ‘0’ equal to or below ‘n’ equal to or below ‘M’ – 1.
Hamming window function – It is a mathematical, bell-shaped tapering function used in digital signal processing (DSP), and applicable in metallurgical analysis of experimental data (e.g., vibration, acoustic emission, or X-ray diffraction signals), to minimize spectral leakage and reduce edge discontinuities when performing Fourier transforms.
Hammock activity – In a schedule network diagram, a hammock activity is a type of summary activity that represents a number of, but unrelated, smaller activities which occur between two dates.
Hamon – In sword-smithing, from Japanese, Hamon literally means ‘edge pattern’. It is the visible, frequently cloudy, wavy line which separates the hardened cutting edge (yakiba) from the softer, more flexible body (ji) of a blade. It is the aesthetic and practical result of differential hardening (or selective quenching), a technique mainly used in traditional Japanese sword-making to create a sword with an extremely sharp, durable edge which does not snap under impact.
Hand – It is the softness of a piece of fabric, as determined by the touch (individual judgment).
Hand brake – It is a small manual folding machine designed to bend sheet metal, similar in design and purpose to a press brake.
Hand chain operated hoist – It is also known as a manual chain hoist or chain block. It is a mechanical lifting device which uses a hand-operated chain to raise, lower, or position heavy loads. It consists of a housing containing a lifting mechanism, a load chain, and a hand chain. The operator pulls the hand chain, which turns gears and a sprocket to move the load chain and lift or lower the load. Parameters to consider when specifying hand chain operated hoists include (i) speed of the lift, (ii) height of the lift, (iii) frequency of the lift, and (iv) weight of the load. Several hoist manufacturers also provide overload protection devices for hand powered hoists, either as standard equipment, or as an added cost option. This device protects the user, the overhead structure and the hoist from an ‘excessive overload condition’. Many of the hoist manufacturers use a friction type, clutched hub, as a part of the hoist’s hand chain wheel. When the pull on the hand chain is large enough to slip the clutch and prevent the load from being lifted, the operator becomes aware that the hoist is overloaded. The capacity of the hand chain hoist is the maximum weight of the load which can be lifted and is usually given in tons. The rated capacity of the hoist is the maximum load for which the hoist is designed by the manufacturer to lift. The lift is the maximum length of travel required for raising and lowering the load and is given in metres. The hand chain drop is the length of chain required for the hand chain of the hoist. The drop is normally around 600 millimeters less than the length of the lift, which prevents the chain from contacting the floor. The actual length of hand chain needed is around 2 times the lift minus 600 mm, as the chain is in a continuous loop when it travels around the hand chain wheel of the hoist. The hoist suspension means how or where the hoist is attached. Most of the hand chain hoists are with a top hook used for single point suspension. They can also be hooked on to a trolley, or built special with a top lug or eyebolt. This allows attachment to a low headroom style trolley for more permanent installations.
Hand equation – It is a mathematical formula developed from regression analysis which quantifies the properties of materials.
Hand factor – It is a, cost-estimating technique used to determine the total installed cost (TIC) of process equipment by multiplying the purchased equipment cost (PEC) by specific factors based on equipment type. It streamlines project estimations by accounting for related installation costs (piping, insulation, electrical). It is a, form of ‘factor estimating’ developed for quickly determining capital costs during feasibility studies.
Hand forge (smith forge) – It is a forging operation in which forming is accomplished on dies which are normally flat. The piece is shaped roughly to the needed contour with little or no lateral confinement, and operations involving mandrels are included.
Hand forging – It is frequently synonymous with blacksmithing or open-die forging. It is the fundamental process of shaping heated metal into desired forms using manual tools, such as hammers, anvils, and tongs. It involves plastic deformation of material, typically heated to a red-hot state, allowing for customized, low-volume production of unique shapes without specialized, high-cost dies.
Handhole – It is an access opening in a pressure part normally not exceeding 150 mm in its longest dimension.
Handhole cover – It is for the closure of a handhole.
Hand ladle – It is a bucket-shaped, refractory-lined vessel with a handle which is designed for manual transporting and pouring of molten metal (such as aluminum, iron, or steel). Ranging from small, single-person tools to larger, two-person ‘shank’ ladles, they typically hold up to 20 kilograms, though some can go higher.
Hand-held calculator – It is a portable computing device which is designed to perform mathematical calculations and is valued for its simplicity and sufficient precision, particularly useful for applications such as quick evaluations of thermal performance and step-wise debugging of computer programmes.
Hand lay-up – It is the process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mould by hand.
Handling – It is the process by which materials are carried throughout the facility, by chain, wire, hook, or racked in a fixture.
Handling breaks – These are irregular breaks caused by improper handling of metal sheets during processing. These breaks result from bending or sagging of the sheets during handling.
Handling equipment – It refers to the mechanical tools, systems, and devices designed to move, store, control, and protect materials and products throughout manufacturing, distribution, and disposal. These systems, frequently called ‘material handling equipment’ (MHE), are classified into transport, positioning, unit load formation, and storage categories to maximize productivity and safety.
Handling life– It is the out-of-refrigeration time over which a material retains its handleability.
Handling mark – For rolled products, it is an area of broken surface which is introduced after processing. The mark normally has no relationship to the rolling direction. For extrusions, it is the damage which can be imparted to the surface during handling operations.
Handling system – It encompasses the methods and equipment used to move, store, control, and protect materials or products throughout a process, from initial acquisition to final disposal. Specifically, material handling systems focus on the efficient and safe movement and storage of materials within a facility or supply chain. These systems can be manual, mechanical, or automated, and are crucial for optimizing productivity, reducing costs, and ensuring workplace safety.
Handover – In the project life cycle, a handover is the point at which deliverables are given to users. It is the formal, systematic transfer of responsibility, data, or physical control of a system / project from one party (e.g., contractor, design team) to another (e.g., owner, operations team). It ensures continuity, safety, and compliance through documentation, training, and verified acceptance criteria.
Handover certificate – It is a formal, signed document certifying the successful transfer of a completed project, system, or equipment from the contractor / supplier to the customer or owner. It confirms that all work meets specifications, inspection standards are met, and necessary documentation is delivered, officially marking the start of the defect liability period.
Handover procedure – It is the systematic process of transferring responsibility, knowledge, and assets for a project, system, or product from one team (e.g., design, construction) to another (e.g., operations, customer). It ensures all documentation, safety protocols, and acceptance criteria are met, facilitating a smooth transition of ownership.
Hand pump – It is a manually operated pump. Hand pumps use human power and mechanical advantage to move fluids or air from one place to another. They are widely used in a variety of industrial activities. There are several different types of hand pump available, mainly operating on a piston, diaphragm or rotary vane principle with a check valve on the entry and exit ports to the chamber operating in opposing directions. Majority of the hand pumps are either piston pumps or plunger pumps, and are positive displacement pumps.
Hand pump, valve – It is a manual mechanical or hydraulic device fitted to an actuator for operating the valve when the normal motive power is not available.
Handshaking lines – These lines refer to the main hardware lines used in data transmission to manage communication between a transmitter and receiver, ensuring that the receiver is ready to accept data.
Hand sinking – It refers to the manual excavation of vertical or inclined shafts, pits, or wells, typically conducted for mining development, civil construction, or water well installation. It is a traditional, labour-intensive method involving manual digging, muck removal (removing broken rock /soil), and installation of support structures without the use of heavy boring machinery.
Hand straightening – It is a straightening operation performed on a surface plate to bring a forging within straightness tolerance. A bottom die from a set of finish dies is frequently used instead of a surface plate. Hand tools used include mallets, sledges, blocks, jacks, and oil gear presses in addition to regular inspection tools.
Hand thread – It defines the helical direction of screw threads, determining if they tighten by clockwise (Right-Hand) or counterclockwise (Left-Hand) rotation. Right-hand (RH) is the standard, while Left-hand (LH) is used for specialized anti-loosening applications like rotating shafts or pedals.
Hand tool – It is any tool which is powered by hand rather than a motor. Categories of hand tools include wrenches, pliers, cutters, files, striking tools, struck or hammered tools, screwdrivers, vises, clamps, snips, hacksaws, drills, and knives.
Hand valve – It is a manually operated device used in piping, hydraulic, and pneumatic systems to start, stop, or regulate the flow of fluids (liquids, gases, or steam). Operated through a handwheel or lever, these valves provide direct, reliable control for isolation, throttling, and maintenance purposes.
Hand-wheel – it consists of a wheel consisting of a rim connected to a hub i.e., by spokes and used to operate manually a valve needing multiple turns.
Hand-wheel operated valve – It is a valve on which the handwheel drives the stem directly to operate the valve.
Hand-wheel rim pull – It is the manual effort (force) needed on the rim of a hand-wheel to open or close the valve. It is normally expressed in Newton.
Hangar – It is a specialized, large-span, enclosed structure designed to provide shelter for aircraft protecting them from weather conditions such as direct sunlight, rain, and snow. It is a high-volume building, frequently constructed from steel, or concrete, and is important for the maintenance, repair, storage, and assembly of aircraft.
Hanger – It is an unplanned break in a network path, normally caused by oversights regarding activities or dependent relationships between activities.
Hanging – Hanging is the phenomenon in the blast furnace which takes place, when the burden materials charged at the top of the blast do not move continuously towards the hearth of the furnace. Hanging originates when the burden, on its way down, meets a very high resistance resulting into the stoppage of the movement of the burden. Hanging takes place due to the bridging of the burden materials in the stack of the furnace. When it occurs, the material below the hang continues to move downward, forming a space which is void of solid material but filled with hot gas at very high pressure. This space continues to grow until the hang finally collapses.
Hanging burr – It is the loose or flexible portions of a burr which are not firmly attached to the work-piece (i.e., hanging from the work-piece). It is sometimes called a flag.
Hanging load – It refers to a force (weight) suspended from a structural member above, such as a beam, truss, or ceiling, rather than supported from below. It is a form of tension-based loading, frequently consisting of dead loads (fixtures, pipes) or specialized structural elements like hanging columns.
Hanging-wall – It is the rock which is on the upper side of a vein or ore deposit. It also refers to any object, including the weight of attachments like hook blocks, shackles, and slings, which is fully lifted and supported by the crane’s hook, without resting on a solid base. This load is considered ‘free’ when not obstructed or partially buried.
Hankel functions – These are also known as Bessel functions of the third kind. These are solutions to Bessel’s differential equation which are specifically formulated to represent incoming or outgoing cylindrical waves. They are particularly useful for modeling scattering, wave propagation (acoustics, electromagnetics), and radiation.
Hankel singular values – These are the square roots of the eigenvalues of the matrix formed by the controllability and observability Grammians. These values are used to compute bounds related to system performance.
Hanning window – It is also called Hann window. It is a type of weighting function used in signal processing, normally in structural health monitoring, noise, and vibration analysis for machinery like cranes, to minimize spectral leakage when converting time-domain data into the frequency domain (using Fast Fourier transform, FFT). It is characterized by a ‘raised cosine’ shape which tapers the edges of a captured data sample to zero, ensuring a smooth transition.
Hansen solubility parameters – These are a set of three numerical values used to predict whether one material (e.g., a solvent, polymer, or pigment) is going to dissolve in another, based on the principle that ‘like dissolves like’. This model breaks down the total cohesive energy density of a substance into three specific intermolecular interaction components namely (i) dispersion forces, (ii) polar interactions, and (iii) hydrogen bonding.
Haptic display – It is an interface which provides tactile (skin-based) and kinesthetic (force / motion) feedback to users, enabling the perception of 3D contours, texture, stiffness, and weight in virtual or remote environments. These devices function as bi-directional, human-computer interaction tools which measure user input (position / force) while simultaneously delivering, or ‘displaying’, force sensations through actuators, motors, or vibrating mechanisms.
Haptics – It involves defining and controlling parameters to simulate the sense of touch, bridging digital data with human perception through actuators, sensors, and controllers. It is divided into two main domains namely (i) cutaneous (tactile) feedback), and (ii) kinesthetic feedback. Engineers define haptic experiences by manipulating several core parameters namely (i) amplitude (intensity), (ii) frequency, (iii) duration / timing, (iv) waveform / shape, (v) spatial location, and (vi) latency:.
Haptic technology – It refers to the use of advanced, computer-controlled interfaces which simulate the tactile and kinesthetic properties of physical materials, such as metal, alloys, and composites, allowing users to feel, manipulate, and test virtual materials in real-time. It is frequently described as ‘virtual clay’ or a ‘digital touch’ system that brings tactile realism to computer-aided design (CAD) and material engineering. It utilizes tactile sensation and control to interact with computer applications, enabling natural communication between humans and computers through simulating physical interactions like clay modeling in a virtual environment.
Harbour – It is a sheltered, partly or fully enclosed coastal water area designed to provide safe anchorage and protection for ships, boats, and barges from high waves, storms, and strong currents. It serves as a, frequently man-made, facility for mooring, repairing, and loading / unloading cargo or passengers, acting as an important interface between waterborne and land transport.
Hard-board – It is a high-density engineered wood fibre-board with a density over 800 kilograms per square meter, produced by compressing exploded wood fibres under extreme heat and pressure. Frequently referred to as high-density fibre-board (HDF), it uses lignin for bonding without added adhesives. Key properties include high durability, strength, no grain, and a smooth, rigid surface.
Hard carbon – It is a non-graphitizable, amorphous material produced by pyrolyzing precursors (e.g., polymers, biomass) at around 1,000 deg C, resisting graphitization even above 2,500 deg C. Characterized by a ‘house of cards’ micro-structure of disordered graphene layers and high micro-porosity, it is a premier anode material for sodium-ion batteries, offering high reversible capacities (around 300 milli-ampere-hours per gram mass, mAh/g) and large interlayer spacing (0.37 nano-meters to 0.4 nano-meters).
Hard chromium – It is the chromium which is electro-deposited for engineering purposes (such as to increase the wear resistance of sliding metal surfaces) rather than as a decorative coating. It is normally applied directly to substrate and is customarily thicker (higher than 1.2 micrometers) than a decorative deposit, but not necessarily harder.
Hard chromium plating – It is produced by electro-deposition from a solution containing chromic acid (CrO3) and a catalytic anion in proper proportion. The metal so produced is extremely hard and corrosion resistant. The process is used for applications where excellent wear and / or corrosion resistance is needed. This includes products such as piston rings, shock absorbers, struts, brake pistons, engine valve stems, cylinder liners, and hydraulic rods. Other applications are for aircraft landing gears, textile and gravure rolls, plastic rolls, and dies and moulds.
Hard coating – In anodizing of aluminum, it is an anodic oxide coating on aluminum with a higher apparent density and thickness and a higher resistance to wear than the conventional coatings.
Hard coatings – These are thin films which are deposited on tool substrates in order to improve their desired properties such as friction, corrosion resistance, hardness, and wear resistance while preserving the bulk material properties. From a functional point of view the most important coating properties are hot hardness, good adhesion to the substrate, and chemical stability. The coating performance can be further improved by optimum coating thickness, fine microstructure, and compressive residual stresses. These properties can essentially be fulfilled only by ceramic materials. In practice, the choice is limited to transition metal nitrides and partly carbides and oxides. Such materials can be reliably deposited in a thin film form by chemical vapour deposition or physical vapour deposition techniques.
Hard coking coal – It is a type of metallurgical coal. It is used in the coke ovens. It is a necessary input in the production of strong coke. It is a premium grade of coal used to produce coke for blast furnace ironmaking. It is a specific type of coal which, when heated in the absence of air, melts, swells, and solidifies into a hard, carbon-rich material called coke. Hard coking coal is a necessary input in the production of strong coke. It is evaluated based on the strength, yield of and size distribution of coke produced which is dependent on rank and plastic properties of the coal.
Hard constraint – It is a design requirement which cannot be relaxed, i.e., a must requirement.
Hard coatings – These are thin films (typically a few micrometers thick) applied to substrates to drastically improve surface properties like high hardness, wear resistance, low friction, and corrosion protection without altering the underlying material’s bulk properties. They are important for extending the life of tools, machinery, and components in automotive, industrial, and medical applications. Common materials for hard coatings include nitrides (titanium nitride, chromium nitride), carbides, oxides, diamond-like carbon (DLC), and boron-based compounds. Techniques used for depositions include ‘physical vapour deposition’ (PVD) and ‘chemical vapour deposition’ (CVD), which allow for precise, high-performance layering.
Hard-core / soft-clad extrusion – It is often referred to as co-extrusion of composite rods / tubes or composite extrusion with a hard core. It is a specialized manufacturing process used to produce bimetallic or composite materials. It involves simultaneously extruding two different materials, a strong, high-strength core (hard-core) and a softer, more ductile outer layer (soft-clad), through a single die to create a unified profile. This method combines the high mechanical strength of the inner material with the specific surface properties (e.g., corrosion resistance, conductivity) of the outer material.
Hard disk – It is a rigid magnetic disk which is permanently fixed within a drive unit and used to store data. It can also be a removable cartridge which contains one or more magnetic disks.
Hard disk drive – It is an electro-mechanical non-volatile storage device which uses rapidly rotating, rigid magnetic platters to store and retrieve digital data. Engineered for long-term storage, it uses actuator arms and magnetic read / write heads to access data in a random-access manner, retaining information even without power.
Hard drawn – It is an imprecise term which is applied to drawn products, such as wire and tubing. It indicates substantial cold reduction without subsequent annealing.
Hard drive – It is a non-volatile device for storing and retrieving digital information, consisting of one or more rigid, rapidly rotating discs coated with magnetic material and equipped with magnetic heads for data writing and reading. It is classified as a random access and magnetic data storage device, widely used in both desktop and embedded systems.
Hardenability – It refers to the ability of a ferrous alloy (like steel) to harden when quenched (rapidly cooled from a high temperature) and the depth to which that hardening effect penetrates. It is not the same as hardness itself, which is a material’s resistance to indentation. Instead, hardenability describes how deeply a steel can be hardened by quenching. Hardenability is the relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is normally measured as the distance below a quenched surface at which the metal shows a specific hardness, for example 50 HRC (Rockwell hardness, C-scale) or a specific percentage of martensite in the micro-structure.
Hardenable alloys – These are metallic materials capable of substantial strength and hardness increases through controlled heat treatment, specifically quenching to form martensite in steels or precipitation hardening (age hardening) in non-ferrous metals like aluminum, copper, and nickel. These alloys rely on specific alloying elements and carbon content (0.25 % to 0.55 % for steel) to control phase transformations and improve performance.
Hardenable low-expansion / constant modulus alloys – These are specialized metallic materials designed to combine extreme dimensional stability (low thermal expansion or constant elasticity) with high mechanical strength achieved through heat treatment. These alloys are mainly based on iron-nickel (Fe-Ni) or iron-nickel-cobalt (Fe-Ni-Co) systems, with additional elements such as titanium, niobium, or aluminum added to enable precipitation hardening (age hardening).
Hardenable steel – It refers to alloys capable of transforming their micro-structure to martensite, a very hard and brittle phase, when heated to an austenitic temperature and cooled rapidly (quenched). It measures the material’s ability to achieve high hardness throughout a specific depth, typically dictated by carbon content and alloying elements.
Hardened cement paste – It is the solid, stonelike, and porous matrix formed by the chemical reaction (hydration) between Portland cement and water, serving as the binding agent in concrete. It mainly consists of calcium silicate hydrate (C-S-H) gel and calcium hydro-oxide, determining the concrete’s strength, permeability, and durability.
Hardened concrete – It is the solidified, cured, and durable composite material resulting from the chemical hydration of cement, water, and aggregates, which has achieved sufficient strength to perform structural functions. It is characterized by high compressive strength, durability against environmental exposure, and the ability to resist structural loads.
Hardened forged steel rolls – These are industrial, cylindrical tools manufactured by forging alloy steel ingots, typically using hydraulic presses to ensure high density, structural integrity, and grain refinement, followed by precise, deep-penetration hardening treatments. They are critical components in rolling mills, engineered to provide high surface hardness (for wear resistance) and a tough, shock-resistant core (for breakage resistance) during hot or cold metal strip, plate, and section reduction.
Hardened material – It is a substance (typically metal or concrete) which has undergone a process to considerably increase its hardness, yield strength, and wear resistance, often at the expense of ductility. This is achieved through heat treatment (quenching), alloying, or mechanical deformation, creating a more durable microstructure like martensite in steel.
Hardened state – It refers to the condition of a material (very frequently concrete or metal) after it has undergone a process of setting, curing, or heat treatment, resulting in increased strength, density, and resistance to deformation or wear. It represents the final, stable structural phase where the material can bear designed loads.
Hardened steel – It is a medium-to-high carbon steel (typically higher than 0.3 % carbon) subjected to heat treatment, specifically heating to the austenite phase (815 deg C to 1,035 deg C), followed by rapid quenching and tempering, to considerably increase hardness, wear resistance, and tensile strength through the formation of tempered martensite. It is necessary for tools and machine parts.
Hardened surface layer depth – It is frequently called case depth. It is the perpendicular distance from the surface of a hardened work-piece to a point where the material properties (normally hardness or micro-structure) blend with the softer, unhardened core. This depth represents the thickness of the wear-resistant ‘case’ produced by treatments such as carburizing, nitriding, or induction hardening.
Hardened zone – It refers to a specific, intentionally modified layer or region within a material (typically steel) with considerably higher hardness and wear resistance than the underlying bulk material (core). Achieved through heat treatment or thermochemical processes like carburizing or nitriding, this zone features a, transformed micro-structure, frequently martensite, designed to improve surface load-bearing capacity while maintaining core toughness.
Hardener – It is an alloy rich in one or more alloying elements which is added to a melt to permit closer control of composition than is possible by the addition of pure metals, or to introduce refractory elements not readily alloyed with the base metal. Sometimes it is called master alloy or rich alloy.
Hardening – It means increasing hardness of metals by suitable treatment, normally involving heating and cooling. Steels can be hardened by the simple means of heating the steel to a temperature higher than the A3 transformation temperature, holding long enough to ensure the achievement of uniform temperature and solution of carbon in the austenite, and then cooling the steel rapidly (quenching). Complete hardening depends on cooling so rapidly that the austenite, which does not decompose on cooling through the A1 temperature and is maintained at relatively low temperatures. When this is accomplished, the austenite starts transforming to martensite on cooling below the ‘Ms’ temperature (around 220 deg C) and is completely transformed to martensite below ‘Mf’ temperature. When applicable, more specific terms are used, e.g., age hardening, case hardening, flame hardening, induction hardening, precipitation hardening, and quench hardening.
Hardening behaviour – It refers to the increase in strength and hardness of a metal as it undergoes plastic deformation, mainly caused by the accumulation and interaction of dislocations within the crystal lattice. This phenomenon, frequently called work hardening or strain hardening, results in higher resistance to further deformation but reduces ductility.
Hardening coefficient – It is a measure of the material’s ability to undergo strain hardening, which is influenced by factors such as micro-structure and plastic deformation, and can decrease below 0.1 when yield strength is increased through heat treatment or cold working. It is a material property that quantifies a metal’s ability to strengthen during plastic deformation, typically ranging from 0 to 0.5.
Hardening curve – It is a graphical representation (true stress against true plastic strain) which describes a material’s increased resistance to deformation as it is plastically deformed. It illustrates how stress increases with strain beyond the yield point, representing the strengthening effect caused by dislocation multiplication and interaction within the crystal structure.
Hardening effects – These refer to the increase in strength, hardness, and load-bearing capacity of materials, particularly metals, resulting from plastic deformation (work / strain hardening) or thermal treatment. This phenomenon is caused by atomic dislocation buildup or grain structure changes, frequently causing increased brittleness and reduced ductility.
Hardening exponent – It is also called strain hardening exponent (n). It is a dimensionless material constant (0 is less than or equal to n less than or equal to 1) which quantifies a material’s capacity to strengthen under plastic deformation. It represents the slope of the flow curve in logarithmic coordinates, indicating how much a metal increases in strength (work hardening) relative to its plastic strain.
Hardening index (n) – It is defined as a precise measure of strain-hardening in materials, indicating the material’s ability to withstand deformation without tearing during processes involving considerable stretching. A higher n-value indicates a higher capacity to resist localized deformation and distribute strain, crucial for sheet metal forming.
Hardening law – It defines how a material’s yield surface change, specifically, how its yield strength increases, as it undergoes plastic deformation. It governs the evolution of material strengthening because of the dislocation movement and generation. Common types include isotropic hardening (expansion of the yield surface), kinematic hardening (translation of the yield surface), and mixed models.
Hardening mechanisms – These are techniques used to increase a metal’s strength and hardness by restricting internal dislocation motion within its crystal structure. Key methods include precipitation hardening, solid-solution hardening, strain hardening (work hardening), and grain refinement, frequently applied through heat treatment (quenching) or cold working.
Hardening model – It is a mathematical or physical framework used to describe and predict the increase in a material’s yield stress and hardness as a result of plastic deformation (strain hardening) or micro-structure changes (precipitation / transformation hardening). These models relate the mechanical response (stress-strain curve) to the underlying physical changes, such as increased dislocation density, solute atom interaction, or the presence of second-phase particles.
Hardening modulus – It is the rate of change of stress with respect to plastic strain during the strain-hardening (plastic) deformation of a material. It represents the slope of the flow curve beyond the yield point, indicating how much the material strengthens as it deforms. It is a measure of a material’s resistance to further deformation, often described as the tangent plastic modulus.
Hardening oil – It is also called quenching oil. It is a specialized oil-based fluid used as a medium to rapidly cool (quench) heated metal, typically steel, to increase its hardness, strength, and wear resistance. It serves as a middle-ground coolant between air (too slow) and water / brine (too fast), providing a controlled, moderate cooling rate which transforms the metal’s structure into martensite while minimizing the risks of distortion, cracking, or breaking.
Hardening parameter – It refers to a variable or coefficient which quantifies how a material’s resistance to plastic deformation changes as it is plastically deformed. It is important for modeling, tracking the evolution of a material’s yield surface during deformation, and predicting material behaviour beyond the initial yield point. Hardening parameters define how a material’s strength increases during plastic deformation or heat treatment, focusing on governing the yield surface evolution (isotropic / kinematic hardening) and material flow stress. Key parameters include the strain hardening exponent (n) which dictates stress change with strain, and flow stress constants (k, m).
Hardening process – It is a heat treatment process which increases a metal’s hardness, strength, and wear resistance by altering its internal structure, typically through heating to an austenitic phase followed by rapid quenching. This process creates a hard, brittle martensite structure, which is frequently tempered to balance toughness and durability, normally applied to steel and some non-ferrous alloys. This process also results in increased brittleness of the metal.
Hardening regimes – These refer to the distinct processes and stages through which a metal’s yield strength and hardness are increased by hindering the movement of dislocations within its crystal structure. The goal of these regimes is to raise resistance to plastic deformation, often at the cost of ductility. The hardening behaviour of metals normally follows a multi-stage process, particularly during work hardening, including (i) athermal hardening (stage I/II), (ii) dynamic recovery (stage III), and (iii) large strain hardening (stage IV/V).
Hardening residual stresses – These are self-balanced internal stresses locked within a metal component after hardening (quenching) or thermo-mechanical processing, remaining without external loads. Mainly driven by non-uniform volumetric changes from martensitic transformation and thermal contraction, they create tensile zones / compressive zones which affect fatigue life and, if excessive, cause distortion.
Hardening response – It refers to the inelastic behaviour of materials characterized by stress redistributions which improve load-bearing and deformation capacities, particularly in structures subjected to non-uniform strains. This response is governed by a strain-hardening law, which indicates how materials strengthen as they undergo plastic deformation.
Hardening rules – These rules define how a metal’s yield surface changes, specifically, how its yield strength increases, during plastic deformation, governing the relationship between stress and strain hardening. These mathematical models describe the evolution of the loading surface, mainly through isotropic hardening (uniform expansion of the yield surface) and kinematic hardening (translation of the yield surface), or a mixed approach, which are critical for modeling material behaviour under cyclic loading.
Hard face – It is a seal facing of high hardness which is applied to a softer material, such as by flame spraying, plasma spraying, electroplating, nitriding, carburizing, or welding.
Hardfacing – It consists of the application of a hard, wear-resistant material to the surface of a component by welding, spraying, or allied welding processes to reduce wear or loss of material by abrasion, impact, erosion, galling, and cavitation.
Hard-facing alloys – These are wear-resistant materials which are available as bare welding rod, flux-coated rod, long-length solid wires, long-length tubular wires, or powders which are deposited by hard-facing. Hard-facing materials include a wide variety of alloys, ceramics, and combinations of these materials. Conventional hard-facing alloys are normally classified as steels or low-alloy ferrous materials, chromium white irons, high-alloy ferrous materials, carbides, nickel-base alloys, or cobalt-base alloys.
Hardfacing processes – These are surface engineering processes which deposit wear-resistant alloys onto metal surfaces. The application of the surface layer can then be performed by one of a number of welding processes namely (i) gas torch welding (combustible gas welding), (ii) manual arc welding, (iii) submerged arc welding, (iii) gas shielded arc welding (tungsten inert gas or metal inert gas), (iv) open arc welding, (v) thermal spraying, (vi) fusion treatment, (vii) plasma spraying (plasma arc welding), (vii) transferred arc plasma, (viii) flame plating, and (ix) deposition process (electroslag welding). Together with the solidification conditions, the quantity of melted base material and base material dilution is important for wear properties. Hardfacing methods differ considerably from each other and also compare with powder spray methods, which show almost no base material dilution because of mixing. Combustible-gas welding offers several advantages in depositing smooth, precise surfaces of high quality. This is done by using a carburizing flame which causes ‘sweating’, or welding of a thin surface layer which spreads freely and prevents metal buildup. For repair of dies, the shielded metal arc method is preferred. It allows high productivity and has the advantage of low heat input and thus minimal distortion of the die cavity.
Hardgrove grindability index – It is a measure for the grindability of coal. Grindability is an index, hence it has no unit. The smaller the Hardgrove grindability index, the harder is coal texture and less grindable is the coal. Grindability is an important factor for the design a coal mill. As grindability depends on many unknown factors, Hardgrove grindability index is determined empirically using a sample mill.
Hard layer – It refers to a purposely engineered, high-hardness, wear-resistant region on the surface of a metal component, while the underlying core remains ductile and tough. This surface layer (frequently called a case) typically has a different, stronger micro-structure and chemical composition than the base metal, designed to withstand localized plastic deformation, surface wear, friction, and abrasion. Hard layers are normally produced by adding hard elements like carbon or nitrogen to the surface, or by developing hard phases (like martensite) through specialized treatments.
Hard machining – It focuses on cutting materials with hardness e.g., 45 HRC (Rockwell hardness scale C) to 68 HRC, directly with cutting tools, frequently replacing grinding for high-precision components.
Hard metal – It is a collective term which designates a sintered material with high hardness, strength, and wear resistance and is characterized by a tough metallic binder phase and particles of carbides, borides, or nitrides of the refractory metals. The term is in general use, while for the carbides the term cemented carbide is preferred, and the boride and nitride materials are normally categorized as cermets.
Hardness – It is a measure of the resistance of a material to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by pressing or abrasion. In general, different materials differ in their hardness. It can be thought of as a function of the stress needed to produce some specified type of surface deformation. There is no absolute scale for hardness, hence, to express hardness quantitatively, each type of test has its own scale of arbitrarily defined hardness. Indentation hardness can be measured by Brinell, Rockwell, Vickers, Knoop, and Scleroscope hardness tests. Macroscopic hardness is normally characterized by strong intermolecular bonds, but the behaviour of solid materials under force is complex, hence, hardness can be measured in different ways, such as scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic, stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.
Hardness, Brinell – It is a measure of a material’s resistance to permanent deformation, determined by pressing a hard, spherical indenter (normally a 10 millimeters tungsten carbide ball) into the material’s surface under a specific load (normally 3,000 kilograms force for steel). It is widely used in heavy engineering and metal production to assess the bulk hardness of materials, especially castings, forgings, and inhomogeneous materials, as it provides a mechanical average value.
Hardness distribution – It refers to the non-uniform variation of a material’s resistance to deformation across its cross-section, frequently caused by thermal processing, welding, or manufacturing techniques like cold-working. It is critical for assessing structural integrity, mapping soft zones in welds, and determining the effectiveness of hardening treatments.
Hardness increases – These refer to the phenomenon where the hardness of a material rises as the grain size decreases, particularly in ultrafine-grained metals, and is influenced by the multiplication and accumulation of dislocations. Hardness increase is achieved by restricting dislocation motion within the metal’s crystal structure through methods like alloying, heat treatment (quenching), cold working (strain hardening), and grain size reduction. Common techniques include quenching to form martensite, precipitation hardening, and surface hardening (carburizing / nitriding), resulting in increased strength and wear resistance. This relationship is exemplified by the Hall–Petch relationship, which indicates that smaller grain sizes correlate with higher hardness values.
Hardness, Knoop – It is determined by a micro-indentation test. It measures the surface hardness of brittle materials (ceramics, glass) or thin coatings by pressing an elongated, pyramid-shaped diamond indenter into the sample. It uses light loads (less than 1 kilogram force) to produce a narrow, elongated diamond-shaped impression.
Hardness, Leeb (H) – It is a dynamic, portable method which determines a material’s surface hardness by measuring the ratio of an impact body’s rebound velocity (Vr) to its impact velocity (Vi). The formula is HL = (Vr/Vi) x 1,000. It is mainly used for rapid, non-destructive testing of large, heavy, or installed metal components.
Hardness, mineralogy – It is normally described as the resistance of a material to being scratched by another material. The ability of materials to resist scratching by another material can be ranked by referring to the Mohs scale which assesses relative hardness of the materials.
Hardness, metallurgy – It is defined as the ability of a material to resist plastic deformation. It is sometimes known as indentation hardness which is the resistance of a material to indentation. The usual type of hardness test is where a pointed or rounded indenter is pressed into a surface of the material under a substantially static load. Hardness measurement can be carried out at macro scale, micro scale or nano scale according to the forces applied and displacements obtained.
Hardness profile – It is also called hardness gradient. It is a graphical or tabulated representation showing the variation in hardness values across a cross-section of a material. Instead of a single value, this profile plots hardness as a function of distance from a surface, through a heat-treated case, or across a welded joint (e.g., from the weld center to the base metal). Hardness profile is the hardness as a function of distance from a fixed reference point (normally from the surface).
Hardness, Rockwell – It is a non-destructive testing method which measures a material’s resistance to permanent indentation (hardness) by measuring the depth of penetration of an indenter under a specific load. A minor load is applied first to establish a reference, followed by a major load. The difference in indentation depth determines the material’s Rockwell hardness number (HR), which is read directly from the machine.
Hardness, Shore – It measures a material’s resistance to surface penetration by a calibrated indenter (needle / cone) under a specific spring force, mainly used for rubber, elastomers, and soft plastics. It indicates material flexibility or rigidity, with higher values (0 to 100) on a given scale (A, D, OO) representing higher hardness.
Hardness testing – Hardness testing is one of the simplest and most widely used inspection methods. It is a non-destructive method which can be used to predict the strength of the metals. Hardness testing consists of pressing an indenter of known geometry and mechanical properties into the test material. The hardness of the material is quantified using one of a variety of scales which directly or indirectly indicate the contact pressure involved in deforming the test surface. Since the indenter is pressed into the material during testing, hardness is also viewed as the ability of a material to resist compressive loads. The indenter can be spherical (Brinell test), pyramidal (Vickers and Knoop tests), or conical (Rockwell test). In the Brinell, Vickers, and Knoop tests, hardness value is the load supported by unit area of the indentation, expressed in kilograms per square millimeter. In the Rockwell tests, the depth of indentation at a prescribed load is determined and converted to a hardness number (without measurement units), which is inversely related to the depth. There exists a correlation between tensile strength and hardness for steels, brass, and nodular cast iron. All the heat-treated steels are subjected to hardness testing to verify that the heat treatment produced the correct hardness and hence strength.
Hardness value – It is a numerical measure of a material’s resistance to permanent (plastic) deformation, typically measured by surface indentation or scratching. It represents a material’s capacity to withstand penetration by a harder indenter under specific loads. Common scales include Rockwell (HRC / HRB), Vickers (HV), and Brinell (HB).
Hardness, Vickers – It is a measure of a material’s resistance to plastic deformation, determined by pressing a 136-degree diamond pyramid indenter into the surface under a specific load. The hardness value is calculated by dividing the test load (in kilogram force) by the surface area of the resulting indentation (square millimeters), rather than its depth.
Hardness, water – It is a measure of the quantity of calcium and magnesium salts in water. It is normally expressed as parts per million as calcium carbonate (CaCO3).
Hardness, Webster – It is determined by Webster hardness tester. The work principle of the Webster hardness tester is to press a steel indenter of a specified shape into the surface of the sample under a certain test force, and use the depth of the indenter to indicate the hardness of the material. The indentation depth of 0.0125 millimeters (normally directly approximated to 0.01 millimeter in actual use) is defined as a Webster hardness unit, represented by HW. The hardness of the material is inversely proportional to the indentation depth. The shallower the indentation, the higher the hardness, and vice versa.
Hard nickel-plating solution – It is an electrolyte, typically nickel sulphate (NiSO4.6H2O), or ammonium chloride (NH4Cl) designed for electro-deposition to produce high tensile strength, wear-resistant, and durable nickel coatings on metal, frequently achieving high hardness levels. It increases surface durability and provides corrosion resistance.
Hard orientations – These refer to specific crystallographic directions within a material which show high resistance to plastic deformation, slip, or twinning under applied loading, resulting in higher yield strength or lower ductility. These orientations normally have a low Schmid factor, meaning the shear stress on their slip systems is low relative to the applied tensile or compressive stress.
Hard particles – These are rigid, non-deformable solid materials characterized by high hardness, specific shapes, and sizes which resist deformation and crushing under stress. In tribology, they are important for causing abrasive wear or acting as strengthening agents within a matrix, considerably impacting material surface integrity and durability.
Hard phase – It is a distinct, physically separated, and rigid component within a material’s micro-structure which provides high strength, hardness, and wear resistance. Typically, these phases consist of crystalline, ceramic, or inter-metallic compounds which resist localized plastic deformation.
Hard points – These points refer to localized, extremely hard, and often brittle regions within a metal component which differ considerably in hardness from the surrounding matrix. These areas are important in failure analysis since they resist deformation and cutting, acting as stress concentrators which lead to premature fatigue or brittle fracture.
Hard rock – It is the rock material typically having a uniaxial compressive strength (UCS) higher than 100 mega-pascals, needing drilling and blasting or specialized, heavy-duty cutters for excavation. These materials are normally igneous, metamorphic, or heavily cemented sedimentary rocks, frequently characterized by substantial strength, density, and, important for stability analysis, well-developed joints or fractures.
Hard rock formations – These are competent, high-strength geological materials typically showing a uniaxial compressive strength (UCS) higher than 100 mega-pascals. These formations, normally igneous or metamorphic, are characterized by low porosity, substantial resistance to deformation, and need specialized techniques like drilling and blasting for excavation.
Hard rock mass – It is a geological formation with a uniaxial compressive strength (UCS) typically exceeding 100 mega-pascals, frequently needing blasting or heavy machinery for excavation. It normally consists of igneous or metamorphic rock with substantial jointing, where stability is determined by the interaction between strong rock blocks and discontinuities, frequently posing risks of rockfalls or seepage.
Hard sand match – It is also called match plate. It is a specialized, durable, and normally metallic plate (aluminum or steel) used in high-production sand casting, where split pattern halves for the cope and drag are mounted on opposite sides of the plate. It is designed to create highly accurate sand moulds at high speeds, frequently used in automated flask-less moulding systems.
Hard segment content – In thermoplastic polyurethanes (TPUs), it refers to the weight percentage of diisocyanates and chain extenders in a copolymer. It determines micro-phase separation, where higher content (typically 5 % to 50 %) increases Young’s modulus, tensile strength, and rigidity by forming interconnected, hard, crystalline domains, while lower content improves flexibility and transparency.
Hard shot peening – It refers to a high-intensity, cold-working surface treatment which uses very hard, spherical media (typically hardened cast steel, ceramic, or cut-wire with high Rockwell C hardness) to strike a metal surface. This process is specifically used to induce deep, high-magnitude compressive residual stresses on the surface layer of a component, which improves considerably its resistance to fatigue failure, stress corrosion cracking, and wear.
Hard soil – It refers to highly compacted, dense earth material, such as stiff clay, boulder-clay, or cemented gravel, which offers high resistance to penetration. It normally needs heavy machinery or picking for excavation, showing high undrained shear strength (frequently higher than 150 kilo-pascals), making it stable for foundations but challenging to excavate.
Hard solder – It is a term erroneously used to denote silver-base brazing filler metals.
Hard surfacing – It is the deposition of filler metal (material) on a base metal (substrate) to get desired properties or dimensions, as opposed to making a joint.
Hard tank – It is a rigid, fixed-volume pressure vessel or storage container constructed from robust materials like steel or reinforced concrete, designed to withstand internal pressure or environmental loads without changing shape. These tanks are typically used for storing liquids, gases, or variable ballast, needing structural integrity and frequently featuring corrosion protection.
Hard temper – It is a temper of non-ferrous alloys and some ferrous alloys corresponding approximately to a cold-worked state beyond which the material can no longer be formed by bending. In specifications, a full hard temper is normally defined in terms of minimum hardness or minimum tensile strength (or, alternatively, a range of hardness or strength) corresponding to a specific percentage of cold reduction following a full anneal. For aluminum, a full hard temper is equivalent to a reduction of 75 % from dead soft, for austenitic stainless steels, a reduction of around 50 % to 55 %.
Hard templating – It is also called nano-casting). It is an engineering, synthesis, and materials science technique which uses rigid, preformed, nano-porous materials (like silica, carbon, or anodic alumina) as templates to create materials with specific, highly ordered nano-structures, such as meso-porous solids. The method involves infiltrating the template’s pores with a precursor, converting it, and removing the template, leaving behind a ‘negative’ replication of the mould.
Hard thresholding – It is a non-linear operator used in signal processing, image processing, and compressed sensing to enforce sparsity by suppressing small-magnitude coefficients. It operates by setting all coefficients with an absolute value lower than a defined threshold ‘T’ to zero, while leaving coefficients exceeding the threshold unchanged.
Hard tooling – It refers to durable, high-cost moulds and dies made from hardened steel, aluminum, or nickel alloys, engineered for high-volume production (thousands to millions of units). It enables precise, consistent, and fast-cycle manufacturing for injection moulding and metal stamping, offering superior wear resistance despite higher upfront costs and longer lead times.
Hard turning – It is a precision engineering machining process which utilizes a single-point cutting tool to remove material from workpieces with high hardness, typically between 45 HRC and 70 HRC (Hardness Rockwell C), such as hardened steel. Frequently serving as a cost-effective alternative to grinding, it achieves high surface finish and dimensional accuracy in a single setup.
Hard X-rays – These are high-energy photons (typically above 10 kilo-electron volts, ranging up to hundreds of kilo-electron volts) with short wavelengths (0.01 nano-meters to 0.1 nano-meters), characterized by high penetrating power through dense materials. Engineered for industrial inspection (non-destructive testing), and structural analysis, they are generated using high voltage (kilo-voltage peak) to accelerate electrons, which then produce bremsstrahlung radiation.
Hard-walled duct – It is a conduit with rigid, non-deformable boundary surfaces where acoustic velocity perturbations normal to the wall are zero. Normally made of sheet metal, these structures (e.g., heating, ventilation, and air conditioning ducts, silencers) are designed to efficiently guide fluid flow or sound waves, facilitating minimal energy loss and low acoustic transmission.
Hardware – It refers to the physical, tangible components of a computer system or electronic device which can be seen and touched. It includes all internal parts, such as central processing unit (CPU), motherboard, random-access memory (RAM) and external peripherals such as monitor, keyboard, mouse, which process, store, and transmit data under the direction of software.
Hardware acceleration – It refers to the utilization of specialized hardware components to perform specific computational tasks more efficiently than general-purpose processors. Within the realm of sustainability, this translates to reducing energy consumption and improving the performance of computationally intensive applications related to environmental monitoring, resource management, and renewable energy systems. It offers a pathway to optimize energy use and enhance the throughput of critical sustainability-related processes.
Hardware accelerator – It is a specialized, purpose-built computing component designed to execute specific tasks, such as AI (artificial intelligence) inference, video encoding, or cryptographic encryption, considerably faster and more efficiently than a general-purpose central processing unit (CPU). While central processing units are designed to handle a broad range of workloads, accelerators are optimized for high-throughput, parallel, or repetitive functions.
Hardware complexity – It refers to the intricate, multi-stage physical infrastructure, equipment, and technological systems needed to extract, refine, process, and cast metals into finished products. It involves the interaction of high-temperature, reactive, and frequently automated systems, such as smelters, casting moulds, and powder metallurgy equipment.
Hardware components – These refer to the physical parts of a system which are interconnected within the hardware architecture, including their roles and relationships as defined by engineering analyses and trade studies. These components encompass different hardware elements which support functionality and performance needs. Hardware components are also the tangible, physical parts of a computing or electronic system that can be touched and seen, forming the infrastructure for processing, storing, and transmitting data.
Hardware cost – It refers to the total expense associated with acquiring, installing, operating, and maintaining the physical tools, machines, and equipment necessary for processing metals. In metal fabrication (such as sheet metal processing) and powder metallurgy, this encompasses both initial capital expenditures and the ongoing costs needed to produce parts.
Hardware debugger – It is a physical device used in engineering to connect a host computer (PC) to a target embedded system (such as a microcontroller, or microprocessor) to monitor, control, and troubleshoot its operation in real-time. It allows developers to halt execution, step through code, inspect memory, and read register values directly on the physical hardware, frequently through interfaces.
Hardware description language – It is a specialized, text-based programming language used in engineering to model, simulate, and synthesize the structure, behavior, and timing of digital logic circuits. Unlike software languages, hardware description languages describe parallel hardware operations and are necessary for designing ‘application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs).
Hardware design – It is the process of creating the physical, tangible components of electronic systems, including schematic design, component selection, system architecture, and PCB (printed circuit board) design. It focuses on how electronic systems operate and is frequently complementary to software development, involving disciplines like electronics, physics, and materials science. Hardware design refers to the conceptualization, planning, and development of physical electronic devices, circuits, and systems.
Hardware development – It refers to the engineering, design, and fabrication of physical metallic components, tools, and structures. It involves manipulating the chemical and physical properties of metals to meet specific performance requirements such as strength, corrosion resistance, and heat resistance.
Hardware element – It refers to the physical, metallic components, parts, and materials used in engineering, construction, and manufacturing. These are typically fabricated from metals and alloys, such as steel, iron, aluminum, copper, and bronze, designed for structural integrity, fastening, or machinery operation.
Hardware features – These features refer to the physical, structural, and compositional characteristics of metallic components, components designed to improve functionality, or specific material attributes achieved through metallurgical processes. These features are critical for determining the strength, durability, and performance of metal products.
Hardware interrupt – It is an electronic signal sent to a computer’s central processing unit (CPU) from an external device (such as a keyboard, mouse, or disk drive) or an internal peripheral, signaling that an event requires immediate attention. When received, the central processing unit suspends its current operations, saves its state, and executes a specialized programme called an ‘interrupt service routine’ (ISR) or interrupt handler to process the event.
Hardware item – It is a manufactured, functional metal component, typically used for fastening, building, or assembly purposes. These items are normally produced from iron, steel, aluminum, copper, or alloys, and are important for providing structural integrity, mobility (hinges), or security (locks).
Hardware multiplier – It is a specialized, dedicated digital circuit within a processor (frequently a digital signal processor or micro-controller) designed to perform high-speed multiplication of two binary numbers. It is a, frequently peripheral, module which uses dedicated transistors to calculate products, frequently acting as part of a ‘multiplier and accumulator’ (MAC) unit.
Hardware overhead – It refers to the indirect, necessary costs and physical infrastructure needed to support the production process, which cannot be directly traced to a specific unit of metal product (such as a single casting or billet). It is often synonymous with manufacturing overhead, factory burden, or production overhead.
Hardware products– These are physical, tangible items, frequently made of metal, designed for specific functional, structural, or mechanical purposes. Metallurgy provides the scientific foundation for these products, focusing on the composition, structure, and processing of metals to achieve desired properties like strength, hardness, and corrosion resistance.
Hardware-software codesign – It is an engineering approach which simultaneously designs a system’s hardware, e.g., application-specific integrated circuit (ASIC) and field-programmable gate array (FPGA),
and software (e.g., application code) to optimize performance, power consumption, and costs. Rather than sequential development, this methodology uses concurrent, integrated design to balance system-level trade-offs, enabling faster time-to-market and improved efficiency for embedded systems.
Hardware-software interface – It refers to the boundary, contract, and interaction point between physical hardware components (processors, memory, peripherals) and the software which controls them (operating systems, drivers, firmware). It is the mechanism by which software sends commands to and receives data from hardware, typically using protocols, registers, and memory-mapped input / output (I/O).
Hardware solution – It normally refers to the physical, mechanical, and industrial equipment used to extract, refine, process, and shape metals, as opposed to the chemical or software processes involved. It includes the physical machinery and apparatus that execute metallurgical operations.
Hardware synthesis – It refers to the process of implementing a ‘control flow state machine’ (CFSM) in a chosen style, where each hardware partition is implemented as a fully synchronous circuit and each software partition is implemented as a ‘C’ stand-alone programme. In this process, a control flow state machine is mapped into an abstract hardware description format, with each transition function implemented using a combinational circuit. The goal is to create a hardware design which accurately represents the behaviour of the control flow state machine.
Hardware system – IT refers to the physical machinery, tools, and equipment used to extract, process, shape, and treat metal materials. Unlike the ‘soft’ aspects of process control (algorithms or chemical recipes), the hardware comprises the tangible assets, such as blast furnaces, rolling mills, and casting machines.
Hardware timer – It is a dedicated, physical electronic circuit, frequently embedded within a time micro-controller, PLC (programmable logic controller), or industrial controller, which tracks the passage of time independently of the main central processing unit (CPU). It functions as a counter which increments or decrements at a fixed, precise rate, frequently using a quartz crystal oscillator, and is used to measure intervals, generate precisely timed pulses (pulse-width modulation, PWM), or trigger interrupts for controlling machinery without overloading the main system processor.
Hardware unit – It is a distinct, tangible, and physical component or module within a computer or electronic system designed to perform specific functions, such as processing, storage, or I/O (input /output) operations. These units, ranging from internal chips (central processing unit, random access memory) to external peripherals, are designed using ‘hardware description languages’ (HDLs) and are typically non-adaptable while running, needing system shutdown for updates.
Hard water – It is the water which contains calcium or magnesium in a quantity which need an excessive quantity of soap to form a lather.
Hardy Cross – It refers to a method of analysis used to solve pipe network problems, where iterative calculations are performed to determine discharges in each pipe by evaluating head loss and applying corrections until the discharge adjustments are minimal.
Haring cell – It is a four-electrode cell for measurement of electrolyte resistance and electrode polarization during electrolysis.
Harmful interference – It is defined as any emission, radiation, or induction which endangers, obstructs, or seriously degrades authorized radio-communication or radio-navigation services. It occurs when unwanted energy disrupts system performance, frequently caused by frequency sharing, spurious emissions, or out-of-band signals.
Harmonic – It is a wave-form which has a frequency which is an integer multiple of another frequency.
Harmonic analysis methods – These refer to techniques which study the non-linear response of materials, particularly in acoustics, vibration, and microstructure design, by decomposing complex signals into fundamental and higher-order harmonic frequency components. These methods are used for non-destructive evaluation of micro-damage or to design advanced, high-performance alloys.
Harmonic analysis in material characterization – It is used as a tool to inspect the material state, micro-damage, or microstructure evolution in metals. It is carried out by nonlinear ultrasonics. When a fundamental wave of finite amplitude is injected into a metal, it generates higher harmonic waves (integer multiples of the fundamental frequency) because of the material’s non-linear elastic behaviour.
Harmonic balance – It is a frequency-domain simulation technique, particularly for nonlinear radio frequency (RF) / microwave circuits and dynamical systems, to determine steady-state, periodic responses. By approximating waveforms as a sum of Fourier series components (harmonics), it converts complex nonlinear differential equations into manageable algebraic equations.
Harmonic components – These are sinusoidal voltage or current elements within an electrical signal which operate at integer multiples of the fundamental power frequency (50 hertz or 60 hertz). Caused by non-linear loads (e.g., drives, computers), they distort waveforms, increasing thermal stress, reducing equipment lifespan, and causing inefficiency in power systems.
Harmonic content – It refers to the components of a periodic voltage or current waveform which are integer multiples of the fundamental power frequency (50 hertz or 60 hertz), causing distortions because of non-linear loads. It is quantified by ‘total harmonic distortion’ (THD), measuring how much a signal deviates from an ideal sine wave.
Harmonic current source – It is a non-linear load, such as power electronics, variable frequency drives, or rectifiers, which draws non-sinusoidal current from the grid. It injects currents at frequencies which are integer multiples of the fundamental 50 hertz /60 hertz power frequency back into the power system.
Harmonic decline – It is a special form of hyperbolic decline characterized by a linear relationship between the reciprocal of the rate of production and time, where the cumulative production over time is logarithmic.
Harmonic distortion – It is an effect of a non-linear signal path which introduces frequencies which are integer multiples of an input frequency.
Harmonic equation – It typically refers to a differential equation modeling oscillatory behaviour, such as ’d-square x / d t-square + w-square x = 0’, where acceleration is proportional and opposite to displacement. It describes simple harmonic motion (SHM) using sine / cosine functions for time-dependent systems, or Laplace’s equation for potential fields.
Harmonic excitation – It is the application of a sinusoidal external force or displacement (sine or cosine wave) to a mechanical system, causing it to vibrate at a constant frequency. It is a fundamental concept in vibration analysis, typically modeling rotating machinery, unbalanced forces, or structural responses to periodic loads.
Harmonic excitation time – It refers to a continuous-wave excitation which is simultaneously applied across a modeled region, allowing for the solution to advance until a steady state is reached, rather than needing propagation across the object. This approach can considerably reduce computation time while getting the desired steady-state response.
Harmonic filter – It is an electrical device designed to mitigate or eliminate harmonic distortion, unwanted frequencies produced by non-linear loads, within power systems. By filtering these distortions, these filters prevent equipment overheating, reduce power losses, and ensure compliance with power quality standards.
Harmonic generation – It refers to the nonlinear, physical process where input energy, typically high-intensity laser light (optical) or alternating current power (electrical), interacts with a medium to produce output signals at integer multiples of the fundamental frequency (2w, 3w, etc.). It is mainly used in photonics to create shorter wavelengths (e.g., ultra-violet) through nonlinear crystals and in power systems as a result of non-linear loads distorting waveforms.
Harmonic light – It is also called optical harmonic generation. It refers to a non-linear optical process where high-intensity lasers interact with materials (such as crystals) to produce new light frequencies which are exact integer multiples (2w, 3w, etc.) of the original fundamental frequency (w). This technique shortens laser wavelengths, normally generating second harmonic generation (SHG) or higher-order harmonics to create ultraviolet or X-ray radiation from visible or infrared sources.
Harmonic mean – It is a kind of average, one of the Pythagorean means. It is the most appropriate average for ratios and rates such as speeds, and is normally only used for positive arguments. The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals of the numbers.
Harmonic motion – It is the simplest form of periodic motion or vibration, characterized by a displacement which repeats each time a rotating element completes a cycle, and can be mathematically expressed as X = Xo sin(wt), where ‘Xo’ is the amplitude, ‘w’ is the angular frequency, and ‘t’ is time.
Harmonic oscillator – It is an oscillator which produces sinusoidal output, such as a simple RLC (resistor, inductor, and capacitor) oscillator.
Harmonic ratio – It is a metric which evaluates signal quality by comparing the energy, power, or amplitude of harmonic components to the total signal or its fundamental component. It normally refers to the ratio of power in the harmonic portion to the total energy (‘harmonics-to-noise ratio’, HNR).
Harmonics – It is the distortion of the power line voltage because of non-linear loads such as rectifiers.
Harmonics in power systems – These are sinusoidal voltages or currents with frequencies which are integer multiples of the fundamental power frequency (50 hertz or 60 hertz). They are caused by non-linear loads, such as power electronics, drives, and computers, which distort the pure sinusoidal waveform. These distortions cause increased equipment heating, poor power quality, and potential system failure.
Harmonic series – It is the divergent infinite sum of reciprocals of natural numbers. While individual terms approach zero, the partial sums increase without bound, meaning it diverges. It is distinct from ‘harmonics’, which are integer multiples of a fundamental frequency.
Harmonic spectrum – It is a frequency-domain representation showing the strength of each harmonic order. It is the representation of the amplitude (and sometimes phase) of individual harmonic components, which are integer multiples of a fundamental frequency (fo), contained within a complex periodic signal, such as voltage, current, or vibration. It graphically displays the distribution of these components, where ‘2fo’ is the second harmonic, ‘3fo’ is the third, and so on.
Harmonic structure design – It a strategic processing method for creating alloys with high strength and high ductility simultaneously. Harmonic structure is a unique topological 3D gradient microstructure consisting of a controlled, non-uniform spatial distribution of coarse-grained (CG) areas surrounded by a 3D network of ultra-fine grains (UFG).
Harmonic time dependence – It refers to the time-varying behaviour of physical quantities which show harmonic oscillations, which can be represented using complex notation, incorporating an oscillatory component defined mathematically to capture the periodic nature of the oscillation.
Harmonics-to-noise ratio – It is a parameter measuring the ratio of periodic (harmonic) signal energy to non-periodic (noise) energy, mainly used to quantify signal quality, such as in speech analysis. A higher harmonics-to-noise ratio indicates a cleaner signal with less noise, while a lower value suggests increased roughness or breathiness.
Harmonic voltage – It refers to distorted sinusoidal voltage components in electrical power systems with frequencies which are integer multiples of the fundamental supply frequency (50 hertz or 60 hertz). Caused by non-linear loads (e.g., rectifiers, variable frequency drives), these distortions deviate from a perfect sine wave, causing overheating, reduced equipment lifespan, and power quality issues.
Harness satin – It is the weaving pattern producing a satin appearance. ‘Eight-harness’ means the warp tow crosses over seven fill tows and under the eighth (repeatedly).
Harmonic voltage source – It is a non-linear load or device which distorts the ideal sinusoidal supply voltage, causing, or injecting, voltage waveforms at frequencies which are integer multiples of the fundamental (50 hertz / 60 hertz) frequency. These sources, such as power electronics and variable frequency drives, produce harmonic currents which, when flowing through network impedances, result in distorted voltage waveforms and power quality issues.
Harmonic wave – It is a continuous, periodic oscillation which propagates through space or a medium, mathematically defined by a sinusoidal (sine or cosine) function. It represents a smooth, repetitive motion with a constant frequency, amplitude, and wavelength. These waves are foundational to modeling sound, light, and mechanical vibrations.
Harmonized standards – These are European standards (EN) developed by recognized bodies, e.g., CEN (European Committee for Standardization), CENELEC (European Committee for Electro-technical Standardization, or ETSI (European Telecommunications Standards Institute) upon a European Commission request to provide technical specifications for complying with EU (European Union) legislation. While voluntary, they offer a ‘presumption of conformity’, meaning products adhering to these standards are presumed to meet mandatory safety and performance requirements. Harmonized standards provide a common technical language, allowing manufacturers to demonstrate compliance with legal requirements e.g., CE (European Conformity) marking. Though using these standards is normally voluntary, they are the most common way to meet necessary safety requirements.
Harpalani – It refers to a permeability model developed to describe the relationship between permeability changes in coal reservoirs and factors such as pressure changes and coal matrix swelling, utilizing a constant volume assumption and matchstick geometry.
Harrison number – It is a dimensionless group used in gas bearing calculations. For thrust bearings, the Harrison number relates viscosity, velocity, pressure, and clearance, and for journal bearings, the Harrison number relates to viscosity, rotational speed, pressure, radius, and clearance.
Harrow – It is also called rake. It is a part of the reclaimer machine for bulk material handling. This reclaiming machine is to traverse the face of a pile of bulk material to be reclaimed. The purpose of the harrow is to control the slope of the face and to agitate the material on the face in a manner such that it falls to the base of the pile face in a regulated manner.
HART communication – The full form of HART is Highway Addressable Remote Transducer. HART communication is a widely used industrial protocol which enables bi-directional digital communication between smart field devices and control systems, typically using the same wires as a 4-20 mA (milli ampere) analog signal. This allows for both process variable data (analog signal) and additional device information (digital signal) to be transmitted simultaneously. HART combines analog and digital communication over a single pair of wires. It is a bi-directional industrial field communication protocol which is used to communicate between intelligent field instruments and host systems.
Hartley oscillator – It is an electronic oscillator which uses a tank circuit comprising inductors and capacitors to generate oscillations, where the inductors can be implemented as a single coil with a centre tap, distinguishing it from the Colpitts oscillator.
Hartmann lines – These are elongated surface markings or depressions, frequently visible with the unaided eye, that form along the length of sheet metal or a tension sample at an angle of 45-degree to the loading axis. It is caused by localized plastic deformation. They result from discontinuous (in-homogeneous) yielding. These are also known as Luders bands, or Luder lines.
Hartmann number – It is a dimensionless quantity in magneto-hydro-dynamics (MHD) which represents the ratio of electro-magnetic (Lorentz) forces to viscous forces in an electrically conducting fluid. It characterizes how a transverse magnetic field influences fluid flow, typically slowing down motion and creating boundary layers.
Hartree potential – It is a scalar potential which corresponds to a given charge density and can be expressed through an integral representation involving the charge distribution. It is used in the context of calculating the effects of charge interactions in different physical systems.
Harvard architecture – It refers to a memory structure in which the processor is connected to two independent memory banks through two independent sets of buses, with one bank typically holding programme instructions and the other holding data. This architecture allows for two memory accesses during a single instruction cycle, improving processing efficiency.
Harvester – It is a system designed to capture and convert energy from environmental sources into usable electrical energy, frequently integrating multiple technologies to improve efficiency and adaptability.
Harvesting efficiency – It refers to the effectiveness of photo-synthetic systems in capturing and utilizing photo-synthetically active radiation (PAR) for energy production, which is influenced by factors such as light saturation and the non-absorption of wavelengths outside the photo-synthetically active radiation spectrum. Maximizing harvesting efficiency needs balancing photo-synthetically active radiation irradiance with the productivity capacity of the system’s components.
Hash – It is a fixed-size string of characters generated from any input data (text, file, password) using a mathematical hash function, used for fast data retrieval in hash tables and important for security by verifying data integrity and storing passwords securely in a one-way process. It maps large, variable-size data to a smaller, unique identifier, allowing for quick lookups and comparisons without revealing the original data.
Hashing algorithm – It is a mathematical function which converts input data of any size into a fixed-length string of characters, called a hash or digest, used for quick data verification, storage, and security. It is a one-way process, meaning one cannot easily reverse the hash to get the original data, making it ideal for password storage and integrity checks where any change in the input drastically alters the output, a property known as the avalanche effect.
Hash table – It is a high-performance data structure which implements an associative array to store key-value pairs, providing average time complexity for insertion, lookup, and deletion. It uses a hash function to compute an index into an array of buckets, mapping keys to specific memory locations.
Hastelloy alloy – It is a corrosion-resistant nickel alloy which contains other chemical elements such as chromium and molybdenum. This material has high temperature resistance and outstanding corrosion resistance. It has good sulphfidation resistance and high metallurgical stability, which makes it preferable material for high-temperature applications of thermal energy storing and electricity generating devices such as gas turbines. In addition, it has low cycle fatigue resistance superior to that of the majority of solid solution-strengthened alloys and it has a very good resistance to hot corrosion. The alloy is used to produce high-temperature gas path components such as turbine combustors, flame holders, liners, pressure vessels of some nuclear reactors, chemical reactors, and pipes / valves in the chemical industry.
Hat channel – It is also called furring channel. It is a cold-rolled, top-hat-shaped metal profile (galvanized steel or aluminum) featuring a flat top, two vertical legs, and outward-flaring flanges. Engineered for structural rigidity and load distribution, it is normally used in, wall, ceiling, and roofing applications to create space, provide attachment points, or decouple materials for acoustic performance.
Hatch distance – It is frequently referred to ‘hatching’ or scan spacing. In additive manufacturing (metal 3D printing, it is defined as the distance between consecutive laser scan paths. While it is a spatial parameter (measured in micrometers, typically 50 micrometers to 150 micrometers, it acts as an important driver of the temperature distribution within the powder bed, since it determines the overlap of molten pools and the heat accumulation from previous passes.
Hatchway – It is a large, frequently rectangular, framed opening on a ship’s deck used for loading cargo and accessing holds. It serves as a structural discontinuity which needs reinforced, watertight covers to maintain vessel strength and security.
Hatschek process – It is a method for producing fibre-reinforced cement products (flat or corrugated sheets) by accumulating thin layers (laminae) of slurry, cement, fibres, and water, on rotating sieve cylinders. It uses a paper-machine-like process to build material thickness, mainly for roofing and cladding.
Haul network – It refers to the transport infrastructure connecting edge network components (such as cell sites) to the core network or backend systems, important for data transmission in tele-communications. These networks, including backhaul and fronthaul, facilitate high-capacity data transfer over short or long distances.
Haul system -It is a combination of equipment, infrastructure, and operational processes designed to move, transport, or lift materials, vehicles, or loads from one location to another. Depending on the context, mining, construction, or mechanical rescue, the definition emphasizes efficiency, safety, and mechanical advantage.
Haul transmission systems – These refer to optical systems capable of transmitting signals over long distances (higher than 1000 kilometers) without needing expensive optical-electrical-optical (OEO) regeneration, addressing system degradations inherent in long fibre transmission links. These systems are engineered to handle high-speed data while managing degradation in optical fibers over thousands of kilometers.
Hausdorff dimension – It is a mathematical measure of a set’s ‘roughness’, complexity, or fractal nature, defining how an object fills space as it is scaled. Unlike topological dimensions (integers), it can be non-integer, characterizing complex structures like fractured surfaces, porous media, or lightning.
Hausdorff measure – It is a generalized, metric-based measure used to quantify the size (length, area, or volume) of irregular or fractional-dimensional sets (fractals) which conventional Euclidean geometry cannot measure. It defines the s-dimensional size of a set by covering it with tiny sets of diameter ‘d’ summing their diameters to the power ‘s’, and taking the limit as d -> 0.
Hawthorne effect – It is the phenomenon where participants alter their behaviour when they are aware of being observed, frequently striving to perform better or adhere to standard operating procedures rather than their normal practices.
Haze – It is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky.
HAZAN – It is ‘hazard analysis’ and covers a range of techniques which are used to analyze hazards. HAZAN includes analyzing the consequences of hazards and the safeguards for hazard prevention / or mitigation.
Hazard – It is any aspect of technology or human activity which produces risk, i.e., the potential for harm or damage to people, property, or the environment. It is a source of danger (i.e., material, energy source, or operation) with the potential to cause illness, injury, or death to a person or damage to a facility or to the environment (without regard to the likelihood or credibility of accident scenarios or consequence mitigation).
Hazard analysis – It is the determination of material, system, process, and plant characteristics which can produce undesirable consequences, followed by the assessment of hazardous situations associated with a process or activity. Largely qualitative techniques are used to pinpoint weaknesses in design or operation of the facility which can lead to accidents. The hazards analysis examines the complete spectrum of potential accidents which can expose members of the public, onsite workers, facility workers, and the environment to hazardous materials.
Hazard analysis and risk assessment – It is a systematic process which involves identifying potential hazards associated with a product, process, or system and subsequently evaluating the probability and severity of harm to determine risk levels.
Hazard and operability (HAZOP) study – It is a structured, systematic, and qualitative examination of a planned or existing process / system to identify risks to personnel, equipment, and the environment, as well as operational inefficiencies. It uses a multidisciplinary team to explore deviations from design intent using guide words (e.g., no, more, and less) on specific system nodes.
Hazard based approach – It is one of several conceptual and analytical approaches to different projects. This approach focuses on identifying and addressing potentially harmful substances or situations, regardless of their actual risk or exposure, aiming to remove or minimize the presence of hazards to protect human health and the environment.
Hazard communication standard – It frequently called ‘HazCom’ or the ‘right-to-know’ law’ It is a regulation needing organizations to identify, classify, and communicate chemical hazards to employees through comprehensive labeling, ‘safety data sheets’ (SDSs), and training. It ensures that chemical safety information, such as physical and health risks, is available to protect employees.
Hazard controls – These are the measures to eliminate, limit, or mitigate hazards to workers, the public, or the environment, including (i) physical, design, structural, and engineering features, (ii) safety structures, systems, and components, (iii) safety management programmes, (iv) technical safety requirements, and (iv) other controls necessary to provide adequate protection from hazards.
Hazard elimination – It is the most effective, top-tier strategy in the hierarchy of controls, defined as the, proactive, physical removal of a hazard, source of danger, or hazardous, process from the workplace or system. It aims to prevent harm by ensuring the hazard is not present, ideally during the design phase.
Hazard evaluation – It is the methodical process of recognizing, evaluating, and addressing potential hazards in a conveyor system to implement suitable safety measures, necessitating consistent updates and adjustments to address evolving conditions.
Hazard function – It is denoted as h(t) or lambda(t). It is a fundamental reliability engineering metric representing the instantaneous failure rate of a component or system at time ‘t’, given it has survived up to that time. It measures the conditional probability of failure in a small interval (t, t + dt), providing a time-dependent risk measure.
Hazard mapping – It is the process of identifying and displaying the spatial variation of hazard events or physical conditions to understand and mitigate potential risks.
Hazardous air pollutants (HAPs) – These are air pollutants which are not covered by ambient air quality standards but which can present a threat of adverse human health effects or adverse environmental effects. Such pollutants include asbestos, beryllium, mercury, benzene, coke oven emissions, radio-nuclides, and vinyl chloride.
Hazardous area – It is a location with a high risk of fire or explosion because of the presence of flammable gases, vapours, liquids, or combustible dust. These areas are classified into specific zones (e.g., zone 0, 1, 2) or divisions based on the probability and duration of a hazardous atmosphere, determining necessary safety measures and equipment, such as explosion-proof, intrinsically safe, or pressurized, as defined by standards
Hazardous chemical – It is a substance (solid, liquid, or gas) capable of causing harm to people, property, or the environment because of its inherent physical or health-related properties, such as toxicity, flammability, corrosivity, or reactivity. These substances need specialized handling, containment, and safety protocols to mitigate risks of explosions, fires, or exposure-related illnesses.
Hazardous event – It is the occurrence of a hazard, normally used in the context of the failure of a safety related system.
Hazardous failure – It is an event where a system, component, or process fails to perform its intended function, resulting in a considerable risk of, or actual, serious injury, death, or large-scale damage to property / environment. It represents a severe, frequently high-consequence failure mode distinct from non-critical functional failures.
Hazardous failure condition – It is a system failure which considerably reduces safety margins or functional capabilities, frequently leading to serious operator distress, excessive workload, or severe injuries to a small number of people. It is a high-risk scenario distinguished from catastrophic (multiple fatalities) and minor failures.
Hazardous limit – It defines the boundary concentration, pressure, temperature, or intensity of a substance or physical agent beyond which it poses an unacceptable risk to human health, property, or the environment. These limits are, in essence, engineered, regulatory, or scientifically determined safe operating boundaries.
Hazardous material – It is that substance which can produce adverse health and / or safety effects to people or the environment.
Hazardous material spill – It means the uncontrolled release of chemical, biological, or radiological agents which pose risks to human health, safety, or the environment. It represents a ‘material out of control, needing specialized handling, personal protective equipment (PPE), or cleanup beyond routine protocols. Such events frequently trigger regulatory reporting.
Hazardous materials identification system – It is a numerical system for rating hazards in the work-place. It is a voluntary system which uses easy-to-understand labels with colours and numbers to accurately communicate and convey hazards of chemicals being used in the facility.
Hazardous substance – It is a material which, because of its quantity, concentration, and physical or chemical characteristics, poses a substantial present or potential hazard to human health and safety or to the environment.
Hazardous waste – It consists of by-products of industrial processes which can pose a substantial or potential hazard to human health or the environment when improperly managed. Hazardous waste possesses at least one of four characteristics namely ignitability, corrosivity, reactivity, or toxicity.
Hazardous waste treatment – It involves processes which reduce or eliminate the hazardous properties of waste materials, making them safer for disposal or reuse, and protecting human health and the environment. Hazardous waste can be treated by chemical, thermal, biological, and physical methods. Chemical methods include ion exchange, precipitation, oxidation and reduction, and neutralization. Among thermal methods is high-temperature incineration, which not only can detoxify certain organic wastes but also can destroy them. Special types of thermal equipment are used for burning waste in either solid, liquid, or sludge form. These include the fluidized-bed incinerator, multiple-hearth furnace, rotary kiln, and liquid-injection incinerator. One problem posed by hazardous-waste incineration is the potential for air pollution. Biological treatment of certain organic wastes is also an option. One method used to treat hazardous waste biologically is called landfarming. In this technique the waste is carefully mixed with surface soil on a suitable tract of land. Microbes that can metabolize the waste may be added, along with nutrients.
Hazard rate – It is the instantaneous rate of failure for a component or system at a specific time ‘t’, given that it has survived up to that time. It represents the probability of failure per unit of time (e.g., failures per hour) and is important for analyzing, comparing, and designing for system reliability. It is a metric which evaluates the risk of failure in a system as it ages, serving as a parameter for comparing different designs in reliability theory. It is not a probability but the limiting value of the probability related to the system’s reliability over time.
Hazard reduction – It is the systematic process of eliminating or minimizing potential sources of harm, risk, or injury in systems, products, or work-places. It involves implementing strategies, inherent, passive, active, or procedural. to ensure safe operational conditions, frequently using the ‘hierarchy of controls’ (elimination, substitution, engineering, administration, personal protective equipment).
Hazard scenarios – These are sequences of initiating and contributory hazards which lead to undesirable events, with potential outcomes influenced by several factors such as equipment condition, human behaviour, and environmental conditions. They are classified into categories based on their impact, focusing on people, environment, and property.
Haze – It is an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky.
HAZID – It is ‘Hazard Identification’.
HAZOP – HAZOP is ‘Hazard and Operability’ study. It is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems which can represent risks to personnel or equipment, or prevent efficient operation. A systematic method of identifying hazards using a team-based approach and applying a set of standard guide phrases to the elements of a design is to determine how these can deviate from the intent of the designers and what the results can be. The method originated in the chemical process industry where it was applied to plant and instrumentation diagrams, but has been adopted more widely and applied to a number of different design descriptions.
H-band steel -It is a carbon, carbon-boron, or alloy steel produced to specified limits of hardenability, the chemical composition range can be slightly different from that of the corresponding grade of ordinary carbon or alloy steel.
H-beam – It is a type of structural member with a H-shaped cross-section. It has equal or near-equal width and depth and is more suited to being oriented vertically to carry axial load such as columns in multi-storey construction. This beam is cost-effective, flexible and is superior in terms of strength, efficiency, higher axial and bending load-bearing capacities. It is a high-performance steel section due to its advantage of optimized cross sectional area distribution and reasonable ratio of strength to weight ratio. With the features of wide flange and thin web, H-beam has a large section modulus, high bending resistance. and excellent mechanical properties. This beam is normally heavier than I-beam and is useful as supports for retaining walls and the like. It can also be used as beam sections where head room is of concern. Because of its outstanding properties, H-beam is a popular section for the designers of steel structures. H-beam is typically made of structural steel and serves a wide variety of construction uses. The horizontal elements of the ‘H’ are called flanges, and the vertical element is known as the web. The web resists shear forces, while the flanges resist most of the bending moment experienced by the beam. The Euler–Bernoulli beam equation shows that the H-shaped section is a very efficient form for carrying both bending and shear loads in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying torsion, for which hollow structural sections are frequently preferred.
H-bridge – It is an array of four controlled switches which coverts direct current to alternating current, with peak value equal to the supply voltage.
Head – It is the height of a vertical fluid column which produces a specific pressure, essentially representing a fluid’s pressure energy as a length (like meters). It quantifies how high a liquid can rise because of its own pressure, calculated as P/dg, where ‘P’ is pressure, ‘d’ is fluid density, and ‘g’ is gravity, making it a key component in Bernoulli’s equation alongside velocity head and elevation head.
Headbox – It is also known as a flow box or flow distributor. It is the important, initial component of a paper machine. It that receives a dilute fibre suspension (stock or pulp) and discharges it in a uniform, controlled layer onto a moving, porous wire/mesh conveyor for sheet formation. Its main function is to deliver a stable, floc-free, and uniform jet of stock across the entire width of the machine, ensuring consistent paper quality (basis weight and fibre orientation).
Head drive conveyor – It is a conveyor system with the drive unit positioned at the discharge end, demanding periodic assessments for precise alignment and efficient operation to guarantee optimal performance.
Header – In forging, header is a type of forging equipment, related to the mechanical press, in which the principal forming energy is applied horizontally to the work-piece, which is gripped and held by prior action of the dies. Header is also an important structural or fluid-handling component which distributes loads or manages pressure. In construction, it is a horizontal beam above openings (doors / windows) transferring structural loads to studs. In mechanical / fluid engineering, it is a manifold or tank that distributes fluid among multiple pipes or regulates pressure.
Head, fasteners – It is the enlarged shape that is formed on one end of the fastener to provide a bearing surface and a method of turning (or holding) the fastener.
Head grade – It is the average grade of ore which is fed into a mill.
Head-hardening – It is a specialized metallurgical heat-treatment process, mainly applied to steel railway rails, which involves rapidly heating the rail head (top surface) and immediately cooling (quenching) it to create a hard, wear-resistant surface layer (martensite) while leaving the underlying rail core (web and base) tough and ductile.
Heading – It is the upsetting of wire, rod, or bar stock in dies to form parts which normally contain portions which are higher in cross-sectional area than the original wire, rod, or bar.
Heading tools – These refer to specialized tooling, specifically punches and dies, used in heading machines to shape metal, frequently wire or rod stock, into fasteners, bolts, rivets, and other complex components. This process, typically performed in cold-heading machines, uses immense pressure to move material, allowing for high-speed, high-volume, and precise production.
Head injury – It is the structural damage or functional impairment of the brain, skull, or scalp resulting from external, physical forces.
Head-loss – It is the reduction in fluid pressure or energy as it flows through a medium, such as a clean bar screen, and can be predicted using specific equations that incorporate factors like approach velocity and the velocity through openings. Clogged screens can result in considerably higher head losses. Head-losses occur at every location where there is a geometric change to the conduit, such as at a bend in the pipeline, a change of section, an obstruction to flow such as a valve, or simply the entry to a pipe or exit from a pipe into a tank.
Head metal – It refers to the excess metal solidified in the runner, gate, and feeding system, which is removed from the finished part after ejection. It is frequently synonymous with, or acts as, the riser or slug in a pressure die cast part. It is the reservoir of metal in the feeder or riser of a mould.
Heading process – It is a metalworking process which incorporates the forging, extruding, and upsetting process. It is frequently performed in the cold state, resulting in cold working. This process typically produces a near net shape work-piece, which means the final product is almost finished although it can sometimes create the final product less plating or heat treating. An important consideration in heading is the tendency for the wire to buckle if its unsupported length to diameter ratio is too high. This ratio is normally limited to less than 3:1 but with appropriate dies, it can be higher. There are a variety of cold heading machines but typically for fastener manufacturing one see one die two blow up to five die six blow and beyond. Multi-die headers allow for more complex parts to be formed as part of one process due to the above limitations of diameter ratio reductions.
Head pulley – It is located at the discharge point of the conveyor. It normally drives the conveyor and frequently has a larger diameter than other pulleys. For better traction, the head pulley is normally lagged (with either rubber or ceramic lagging material).
Headroom – It refers to the vertical clearance between a surface (like a floor or deck) and the lowest overhead obstruction. This obstruction can be a ceiling, beam, or any other part of a structure. It is essentially the ‘free space’ above a surface which allows for safe and comfortable passage or operation. In case of hoists, headroom dimension is the distance between the bearing surfaces of the upper and lower hook at the high hook position (or the minimum distance between the hooks). Headroom dimensions are important for those applications which require operation in close quarters (low ceilings, obstructions, and short lifts etc.).
Heads – Heads are the steel plates which close off the ends of the boiler drum. They are also referred to as end plates. If the shell contains tubes which are held in position by the heads, then they are normally called tube sheets.
Head-space – It is the space between the level of the contents of a container and the closure. Head-space is needed to allow for expansion of a product because of heat or pressure, and to allow the container to be grasped without spilling the contents.
Healed-over scratch – It is a scratch in a metallic object which has occurred in an earlier mill operation and has been partially masked in subsequent rolling. It can open up during forming.
Health, safety, and environment (HSE) – It is a multidisciplinary approach designed to manage and control work-place hazards, environmental risks, and employee well-being. It combats potential sources of physical, chemical, biological, ergonomic, and psychosocial hazards, ensuring the health and safety of the employees and minimizing the impact of operations on the environment. Health, safety, and environment management is frequently used in industries such as iron and steel, oil and gas, mining, manufacturing, construction, and chemical processing, where inherently hazardous conditions are normal.
Health and safety programme – It is a systematic combination of activities, procedures, and facilities designed to ensure and maintain a safe and healthy work-place.
Health impact assessment (HIA) – It is an assessment, normally carried out in advance of a particular project or course of action being approved, which seeks to analyze the likely impact on human health. The health impact assessment is to be used as a tool by decision-makers for the determination of the alternatives which have lesser impacts on health.
Healthy environment – It is a managed, sustainable, and safe, built or natural surrounding which minimizes pollutants, hazards, and stressors to promote human and ecological well-being. It involves applying technical solutions, such as water treatment, air filtration, and waste management, to ensure, for example, clean air, potable water, and safe waste disposal.
Healthy equipment – It is the machinery operating within its intended design parameters, showing optimal performance, reliability, and safety, with low risk of unexpected failure. It is a quantitative and qualitative measure of a machine’s current state compared to its optimal condition, frequently determined by tracking metrics such as vibration, temperature, and wear.
Healthy work environment – It is a safe, supportive, and empowering organizational culture where employees’ physical and mental well-being is prioritized, reducing stress and injury while boosting productivity. Key elements include psychological safety, open communication, work-life balance, and, a collaborative approach to continuous improvement of the psychosocial and physical workspace.
Heap leaching – It is a process whereby valuable metals, normally gold and silver, are leached from a heap, or pad, of crushed ore by leaching solutions percolating down through the heap and collected from a sloping, impermeable liner below the pad.
Heap sand – It is also referred to as system sand or backing sand. It is the bulk moulding sand which has been previously used, reclaimed, and ‘heaped’ on the foundry floor for reuse in creating moulds. It is mainly used as backing sand, the material which fills the majority of the mould flask, supporting the facing sand which directly touches the pattern.
Hearth – It is the bottom portions of certain furnaces, such as air furnaces, and other reverberatory furnaces, which support the charge and sometimes collect and hold molten metal. In blast furnace, it is crucible shaped bottom of the blast furnace where produced hot metal accumulates before it is tapped. It is normally lined with carbon blocks. In industrial furnaces, hearth supports or carries the load for heating. It consists of refractory materials supported by a steel structure, part of which can be water-cooled.
Hearth bottom – It refers to the lower section of a blast furnace where molten iron collects, and its design, including dimensions and sloping, affects the flow and wear characteristics of the furnace.
Hearth diameter – it is the diameter of the inside face of the refractory lining of the blast furnace hearth, excluding any increases in wall thickness at the tap holes.
Hearth line – It is the horizontal line at the intersection of a vertical line through the nose of the tuyere cooler and sloping line of the bosh. With ceramic lined boshes, the line through the noses of the bosh plates determines the slope of the bosh.
Hearth zone, blast furnace – In this zone, the collection and separation and storing of hot metal and liquid slag takes place. The only activities which take place in this zone are desulphurization and carburization of hot metal. The liquid permeability is also important in this zone. The desirable measurements in this zone are (i) level of hot metal and slag and their behaviour, (ii) coke supply and its removal because of its combustion, (iii) desulphurization and carburization of hot metal, and metalloid reaction. Typical measurements in this zone which are needed are monitoring of the behaviour of hot metal and liquid slag as well as monitoring of hearth coke replacement and for this an estimation model using various mathematic models is presently being used.
Heat – It is a stated tonnage of metal obtained from a period of continuous melting in a furnace such as basic oxygen furnace, cupola, or the melting period required to handle this tonnage. In thermo-dynamics, heat is energy in transfer between a thermo-dynamic system and its surroundings by modes other than thermo-dynamic work and transfer of matter. Such modes are microscopic, mainly thermal conduction, radiation, and friction, as distinct from the macroscopic modes, thermo-dynamic work and transfer of matter. For a closed system (transfer of matter excluded), the heat involved in a process is the difference in internal energy between the final and initial states of a system, and subtracting the work done in the process.
Heat-activated adhesive – It is a dry adhesive which is rendered tacky or fluid by application of heat, or heat and pressure, to the assembly.
Heat activation – It is the process of using thermal energy to initiate chemical or physical reactions, such as curing adhesives, curing polymers, or triggering functional materials. It involves increasing the temperature to help molecules overcome an energy barrier, enabling processes like bonding, sintering, or phase changes.
Heat-affected zone (HAZ) – It is that portion of the base metal which has not been melted during brazing, cutting, or welding, but whose micro-structure and mechanical properties have been altered by the heat.
Heat analysis – It is a chemical analysis conducted by the foundry /steel melting shop which measures the exact chemical composition of a particular batch of molten metal. It does not include physical properties testing of which are done on the rolled product after rolling.
Heat and mass transfer factor – It is that portion of the heat and mass transfer equations which relates to the cellular structure.
Heat and power co-generation – It is the simultaneous, sequential generation of electricity and useful thermal energy (heating or cooling) from a single fuel source, such as natural gas, biomass, or waste heat. By recovering otherwise wasted heat, it increases efficiency to 65 % – 90 %, compared to around 35 % for conventional generation.
Heat available – It is the thermal energy above a fixed datum which is capable of being absorbed for useful work.
Heat balance – It is an accounting of the distribution of the heat input, output, and losses.
Heat biomass – It involves the systematic conversion of organic materials, such as wood, agricultural residues, and waste, into thermal energy through processes like direct combustion, gasification, or anaerobic digestion. It is a renewable energy technology designed to replace fossil fuels for heating, offering high-efficiency solutions through specialized boilers and systems.
Heat bonding – It is also called thermal bonding. It is a process which uses controlled heat, frequently combined with pressure, to melt and fuse thermoplastic materials or fibres together without adhesives. Common methods include calender, through-air, and ultrasonic bonding, which solidify to create durable, strong, and flexible joints in applications like composites, and electronics.
Heat build-up – It is the rise in temperature in a part resulting from the dissipation of applied strain energy as heat or from applied mould cure heat.
Heat capacity – It is also known as thermal capacity. It is a physical property of matter, defined as the quantity of heat to be supplied to an object to produce a unit change in its temperature. The SI (International System of Units), unit of heat capacity is joule per kelvin (J/K). Heat capacity is an extensive property.
Heat capacity method – It is a temperature-based analytical approach which relates the energy needed to change a material’s temperature to its mass, frequently used for modeling transient heat transfer, thermal storage, and phase changes. It defines the energy (Q) needed for a temperature change (dT).
Heat capacity rate – It is the product of a fluid’s mass flow rate and its specific heat capacity. It defines the rate at which a flowing fluid can absorb or release heat per unit temperature change, normally measured in W/K or J/(s·K).
Heat check – It is a pattern of parallel surface cracks which are formed by alternate rapid heating and cooling of the extreme surface metal. These are sometimes found on forging dies and piercing punches. There can be two sets of parallel cracks, one set perpendicular to the other.
Heat checking – It is a process in which fine cracks are formed on the surface of a body in sliding contact because of the build-up of excessive frictional heat.
Heat cleaned – It is a condition in which glass or other fibres are exposed to high temperatures to remove preliminary sizings or binders not compatible with the resin system to be applied.
Heat collector element – It is also called absorber tube. It is the central component in parabolic trough solar thermal systems, designed to convert concentrated solar radiation into high-temperature thermal energy (300 deg C to 400 deg C) for electricity generation. It consists of a stainless-steel tube with a selective coating, enclosed within an evacuated glass envelope to minimize heat loss, with specialized bellows for thermal expansion and getters to maintain vacuum.
Heat conduction – It is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature.
Heat-conduction analysis – It is the study of thermal energy transfer through metal objects through atomic vibrations and free-electron movement, driven by temperature gradients. It determines temperature distribution and heat flux, utilizing Fourier’s law to model transient or steady-state heat flow, which is critical for optimizing casting, welding, and heat-treatment processes.
Heat-conduction equation – It is a partial differential equation derived from Fourier’s law and energy conservation, defining how temperature changes over time and space. It models internal heat transfer within solids (e.g., during casting, welding, heat treatment) based on thermal conductivity, material density, and specific heat capacity.
Heat conduction problem – It involves modeling the transfer of thermal energy through a material (solid, liquid, or gas) because of the molecular interactions without bulk motion, driven by a temperature difference. It needs defining the geometry, material properties (thermal conductivity), boundary conditions, and time dependence (steady-state or transient) to calculate temperature distribution or heat flow rate.
Heat conduction process – It is the transfer of internal thermal energy through direct molecular interaction, collisions and lattice vibrations, from higher to lower temperature regions within a substance (solid, liquid, or gas) without bulk material motion. It is driven by a temperature gradient, quantitatively described by Fourier’s law, and occurs mainly in solids.
Heat-conductivity – It is also called thermal conductivity. It is the intrinsic ability of a metal to conduct heat through its structure, measured as the rate of heat flow per unit area per unit temperature gradient (W/m·K). It defines how quickly a metal transfers heat via free electrons, important for processes like casting, welding, and heat treating.
Heat convection – It occurs when the bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid can be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), hence influencing its own transfer. The latter process is frequently called ‘natural convection’. The former process is frequently called ‘forced convection’. In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means.
Heat cycle – It is a series of linked thermodynamic processes, involving heat transfer and work, which return a working fluid to its initial state, converting heat energy into mechanical work or vice versa. Examples include the Carnot, Rankine, Otto, and Diesel cycles.
Heat deflection temperature – It is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in several aspects of product design, engineering and manufacture of products using thermo-plastic components.
Heat demand – It defines the total thermal energy needed to maintain a specific, comfortable indoor temperature (typically around 20 deg C or for industrial processes, accounting for transmission heat losses through the building envelope and ventilation needs, minus solar and internal heat gains. It is normally expressed in kilo-watt hour or mega-watt hour over a period, frequently normalized per square meter per year.
Heat detector – It is a fire safety device designed to trigger an alarm when ambient temperature rises rapidly or hits a specific threshold, indicating a fire. Unlike smoke detectors, they react to convective thermal energy, making them ideal for high-dust / smoke environments like kitchens or garages to prevent false alarms.
Heat diffusion equation – It is a parabolic partial differential equation (PDE) that models the time-dependent spread of thermal energy (temperature) through a solid medium based on Fourier’s law of heat conduction and the principle of energy conservation. It represents the temperature change over time as a function of thermal diffusivity, spatial distribution, and internal heat generation. It is used to determine the temperature field in a medium, needing boundary conditions such as temperatures and heat fluxes for a unique solution.
Heat-disposable pattern – It is a pattern formed from a wax-base or plastic-base material which is melted from the mould cavity by the application of heat.
Heat distribution – It refers to the manner in which thermal energy is transferred, spread, and managed within a system, object, or environment, frequently resulting in specific temperature gradients. It encompasses conduction, convection, and radiation to optimize efficiency, achieve equilibrium, or meet operational requirements.
Heat distribution network – It is an engineered, interconnected system of insulated pipes, pumps, and heat exchangers which transfers thermal energy (hot water or steam) from a central, frequently renewable, source to multiple buildings for space heating and hot water. This system optimizes energy efficiency, allows for heat recovery from waste sources, and reduces carbon emissions by replacing individual boilers.
Heat distortion temperature – It is the temperature at which a standard test bar (a simple cantilever beam) deflects a specified quantity under a stated load.
Heated cylinder – It is a cylindrical model used to measure heat transfer, which differs from flat plate methods because of its geometry and the resultant chimney effect at lower wind magnitudes, affecting total heat transfer. The thermal resistance of the heated cylinder is calculated based on its heating power, the surface area of the tested material, and the temperature difference between the cylinder surface and the surrounding air.
Heated-roll rolling – It is a process to roll difficult-to-work materials. Heated-roll rolling is an isothermal or near-isothermal process in which the work rolls are heated to the same or nearly the same temperature as the work metal. The technique has been demonstrated for sheet rolling on modified conventional rolling mills with either two-high or four-high arrangements. In the two-high arrangement, where the rolls are relatively large, a composite roll design has frequently been used. his consists of rolls with outer sleeves made of a high-temperature superalloy and with cores of hot-work tool steels. Such a design satisfies the need for a roll with good hot hardness at temperatures in the 815 deg C range at a cost less than that of a solid roll made from an expensive superalloy. This setup is improved by induction heating the roll surfaces and by internal water cooling of the core of the rolls and roll bearings. The viability of heated roll rolling also has been demonstrated on a four high mill. In this case, the work rolls and the backup rolls have been heated by banks of radiant heaters and had a design maximum operating surface temperature of 815 deg C for the work rolls.
Heat emission – It is the process of releasing thermal energy from a system, device, or material into its surrounding environment, mainly through convection and radiation, as a by-product of energy consumption or operation. It is an important factor in building energy analysis, thermal management, and mitigating the urban heat island effect.
Heat energy – It is the internal kinetic energy transferred between systems or substances because of a temperature difference, moving spontaneously from higher to lower temperatures. Organized into three main transfer mechanisms, conduction, convection, and radiation, this energy is measured in joules which is SI (International System of Unit) unit, or calories.
Heat engine – It is a system which converts heat or thermal energy, and chemical energy, to mechanical energy, which can then be used to do mechanical work.
Heat enhancement techniques – These are also called heat transfer augmentation techniques. These techniques are methods designed to increase the thermal performance of systems, such as reducing the size or increasing the efficiency of heat exchangers. These techniques intensify heat transfer rates by increasing surface area, improving turbulence, or promoting secondary flows.
Heater – It is a device or component designed to transfer thermal energy to a metal or alloy to induce a physical or chemical change, such as in heat treatment (annealing, tempering, hardening) or during the processing of materials. These devices function by converting electrical energy or fuel combustion into high-temperature heat, typically operating through convection, conduction, or radiation.
Heat exchanger – It is a device which transfers heat from one system to another without physical transfer of any matter. It transfers heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids can be separated by a solid wall to prevent mixing or they can be in direct contact. The heat exchangers are widely used in space heating, refrigeration, air conditioning, power stations, iron and steel plants, chemical plants, petro-chemical plants, petroleum refineries, natural-gas processing, and sewage treatment.
Heat exchanger applications – These refer to the use of heat exchangers in different systems to recover waste heat, improve system efficiency, and minimize energy losses. These applications include configurations such as shell-and-tube, plate, and coil-finned heat exchangers, which are designed to optimize thermal performance in diverse engineering contexts.
Heat exchanger design – It is the systematic process of sizing, configuring, and optimizing equipment to transfer thermal energy between fluids at different temperatures. It involves balancing thermal performance (duty), hydraulic requirements (pressure drop / flow), and mechanical integrity while minimizing capital and operating costs.
Heat exchanger network – It is an interconnected system of heat exchangers, process streams (hot and cold), and utilities designed to maximize energy recovery and minimize external utility usage (heating / cooling) within industrial processes. It optimizes heat transfer between streams to lower operational costs and reduces carbon emissions.
Heat exchanger pile – It is also called energy pile’ It is a multifunctional foundation element which combines structural load-bearing capacity with ground-source heat exchange. These foundation piles, typically 15 centimeters to 3 meters in diameter and 10 meters to 60 meters long, contain high density poly-ethylene (HDPE) pipe loops which circulate fluid to exchange heat with the surrounding soil for building heating and cooling.
Heat exchanger reactor – It is a process intensification device which combines chemical reaction and heat transfer within a single unit. It features high heat-transfer capabilities, frequently coupling exothermic and endothermic reactions (e.g., oxidation and steam reforming) in distinct catalytic zones or a compact, tubular design, resulting in high thermal efficiency.
Heat exchanger area – It is the total surface area of the separating wall (tubes or plates) in direct contact with both hot and cold fluids, through which thermal energy is transferred. It is a critical design parameter defining equipment size, efficiency, and cost.
Heat exchanger surface – It is the physical boundary (plates, tubes, or fins) separating fluids, acting as the interfacial area where thermal energy transfers. Engineering design aims to maximize this area (A) relative to volume, typically calculated by ‘A = pi x D x L x N’ for tubes, to improve heat transfer efficiency.
Heat flow – It is the heat energy which flow in and between materials (solid / liquid / gas) as a result of a temperature difference. It is a process function (or path function).
Heat-flow analysis – It is a specialized branch of thermal analysis which measures the rate at which heat energy is absorbed or released by a metal or alloy sample as it is heated or cooled. It is used to study physical and chemical changes, such as melting, solidification, phase transitions, and crystallization, as a function of time or temperature.
Heat-flow and thermal-conductivity sensors – The accurate measurements of heat flow through thermal insulators and of the thermal conductivity of construction materials are both important. Such measurements are of interest for the purpose of safety and energy conservation. A common heat flow meter design involves the placing of a thin plate of known thermal conductivity on a heat radiating surface. It has been found that the heat flow through these elements is directly related to the temperature difference through them. This temperature difference is frequently detected by thermopiles, a large and even number of thermo-couples connected in series in such a manner that their high-temperature junctions are on the inside and their low-temperature junctions are on the outside surface of the sensing element. The heat flows which are encountered in different processes range from around 10 kilo-calories per square metre hour through freezer walls to around 100,000 kilo-calories per square metre hour through the shells of water-cooled electric furnaces. The thickness of the sensor plates is a few millimeters, and the plates are made of rubber, organic materials, or other heat-resistant materials, sometimes contained in a thin, stainless steel disk case.
Heat flow density – It is the rate of heat energy transfer per unit area across a surface, representing both the magnitude and direction of heat flow. It is a vector quantity, often derived using Fourier’s law of conduction as the product of thermal conductivity and the negative temperature gradient.
Heat flux – It is the rate of thermal energy transfer per unit area across a surface, representing the intensity of heating or cooling during processes like casting, quenching, or smelting. It is a vector quantity indicating both the magnitude and direction of heat flow, driven by temperature gradients. It is the quantity of heat (Q) transferred per unit time (t)through a specific surface area (A), expressed as ‘Q/A.t’. Heat flux can be conductive (through solid metal), convective (fluid motion in casting/cooling), or radiative.
Heat flux density – It is the rate of heat energy transfer per unit area flowing through a surface, representing the intensity of heat flow (conduction, convection, or radiation) in a specific direction. It is a vector quantity indicating both magnitude and direction, frequently calculated using Fourier’s Law.
Heat flux gauge – It is also called heat flux sensor. It is a transducer which measures the rate of thermal energy transfer per unit area passing through a surface, accounting for convection, conduction, and radiation. It produces an electrical output (voltage) proportional to the local heat flow, typically using a thermopile or differential thermocouple.
Heat flux measurement – It is the quantification of the rate of thermal energy transfer per unit area passing through a surface, representing the intensity of heat conduction, convection, or radiation. It is a vector quantity indicating both magnitude and direction, used to monitor, optimize, or analyze thermal systems.
Heat flux sensor – It is also called heat flux transducer. It is an instrument which measures the rate of thermal energy transfer per unit area across a surface. It acts as a transducer, converting conductive, convective, or radiative heat flow into a linear electrical signal (typically milli-volts) proportional to the heat rate.
Heat flux vector – It is a vector quantity which represents the rate of heat energy transfer per unit area across a surface, including both direction and magnitude. The SI (International System of Units) unit is watts per square meter It points in the direction of maximum heat flow (from hot to cold) and is normally perpendicular to isothermal surfaces.
Heat flux zones – These are distinct areas in engineering, particularly in plasma or heat transfer systems, defined by specific, varying rates of energy flow per unit area (watts per square meter). These regions are characterized by non-uniform heat loads (e.g., in divertors or industrial boilers) influenced by magnetic topology or fluid dynamics.
Heat generation – It refers to the production of thermal energy within a metallic material or processing system, caused by physical, chemical, or mechanical processes. Key sources include friction during deformation or machining (mechanical), electrical resistance heating (joule/ohmic), or exothermic reactions (chemical).
Heat generator – It is a device that converts fuel (through combustion) or electricity into thermal energy to satisfy heating demands. These systems, including boilers, burners, and heat pumps, are important for industrial processes, power generation, and space heating. Efficiency is calculated as the useful heat output divided by the energy input.
Heating – It is a fundamental, controlled thermal process where metals or alloys are raised to specific, high temperatures, below their melting point, to alter their microstructure, physical, and mechanical properties. It is the initial stage of heat treatment (heating, soaking, and cooling) designed to relieve internal stresses, soften materials, harden surfaces, or improve ductility.
Heating coil – It is an electrical resistance element, typically made of alloys like nickel-chromium (nichrome), designed to convert electrical energy into thermal energy for heating air, water, or other fluids.
Heating collector – It is also referred to as a solar thermal collector. It is a specialized heat exchanger device designed to absorb solar radiation and convert it into thermal energy. This energy is transferred to a heat transfer fluid (HTF), such as water, air, or antifreeze, for use in domestic hot water, space heating, or industrial processes.
Heating curve – It is a line graph plotting temperature (y-axis) against heat added or time (x-axis) to show a substance’s temperature changes and phase transitions (solid, liquid, gas) as it is heated. It highlights sloped regions (temperature rising, specific heat) and plateaus (constant temperature, phase change / latent heat).
Heating cycle – It is a thermodynamic process, normally acting as a heat pump or heating system, designed to move heat from a lower-temperature environment to a higher-temperature, occupied space. In industrial contexts, it refers to the repeated process of raising a material’s temperature, holding it, and cooling it.
Heating data – It refers to the longitudinal collection of measurements related to indoor room temperature, temperature setpoints defined by users, and controller output, typically recorded at specific intervals to analyze household heating performance.
Heating effect – It refers to the conversion of electrical power into heat when electric current flows through a resistance, which can result in sufficient heat generation to melt conductors and interrupt current flow in protective devices like fuses.
Heating equipment r- It refers to industrial devices designed to generate and transfer thermal energy to metallic materials, ores, ingots, billets, or finished parts, to facilitate physical or chemical transformations, such as melting, smelting, refining, or heat treatment. This equipment typically operates at high temperatures (frequently higher than 400 deg C) and includes furnaces, ovens, and kilns which use combustion or electrical energy to alter the micro-structure, hardness, or composition of metals.
Heating factor – It is frequently referred to within the context of heating rates or thermal diffusivity. It is a measure of the efficiency and speed at which a metal work-piece absorbs heat during thermal processing (such as annealing, hardening, or forging). It represents the time-temperature relationship needed to raise a material’s temperature, directly influencing the micro-structure, grain growth, and final properties of the metal.
Heating load – It is the calculated rate of heat energy needed to be added to a space to maintain a specific, comfortable indoor temperature during cold conditions. It represents the total heat loss from a building through walls, windows, roof, and infiltration, often measured in watts, or kilocalories per hour. The load calculation includes heat transfer through conduction, convection, radiation, and infiltration.
Heating loop – It is a closed-circuit subsystem within a HVAC (heating, ventilation, and air conditioning) or process system which circulates a heat transfer fluid, typically water or glycol, to move thermal energy from a source (e.g., boiler, heat pump) to demand points (e.g., heating coils, radiators). It operates independently using pumps, valves, and controls to regulate temperature.
Heating panel – It is an engineered, low-profile device designed for space heating or industrial processing which emits heat through radiation and natural convection from a large, flat surface. These panels utilize either electric resistance elements or fluid-filled pipes (hydronic) embedded in panels, walls, floors, or ceilings to provide consistent, uniform warmth.
Heating period progresses – This term refers to the advancement of time during which a material is subjected to heating, leading to changes in temperature distribution and thermal stress within the substrate material, particularly affecting the tensile and compressive stress behaviour at different depths below the surface.
Heating power – It is the rate at which thermal energy is generated or transferred to a system, typically measured in watts or Joules per second. It represents the nominal heat output of a system (e.g., heating rod) or the capacity to raise a material’s temperature over time.
Heating practice – It is the heating regime consisting of rate of heating (temperature increase), intermediate and final temperatures, heating and holding times, and soaking temperatures as well as the method and equipment used for heating.
Heating process – It is a method aimed at raising the temperature of a material, potentially resulting in changes to its properties, using different forms of energy. The power needed for this process varies based on the applied heat transfer principle and the desired temperature.
Heating rate – It is the speed at which the temperature of a material or system increases, typically measured in degrees Celsius per minute or per second. It is a critical parameter in materials science (e.g., sintering), chemical processing, and thermal analysis, directly influencing reaction kinetics, grain growth, and phase transformations.
Heating seasonal performance factor – It is a metric measuring the total seasonal heating efficiency of an air-source heat pump. Defined as the ratio of total seasonal heat output (in joules or kilo-calories) to total electrical energy consumed (in watt-hours). A higher heating seasonal performance factor indicates higher energy efficiency. It represents performance over a full heating season, including both the compressor operation and the supplementary resistance heat.
Heating steel – It refers to the process of subjecting steel to specific temperature ranges as part of heat treatment, which is necessary for improving its properties to meet the requirements of different high-end applications.
Heating surface – It is that surfaces which is exposed to products of combustion on one side and water on the other. This surface is measured on the side receiving the heat.
Heating time – It refers to the specific duration need to raise the temperature of a metal component from ambient temperature to a designated target temperature. It depends on the heating method, heat transfer characteristics, and the shape or size of the part.
Heating transformation – It is the phase transformation upon heating. It refers to the structural or phase changes a material undergoes as its temperature increases, frequently needing superheating to form critical nuclei of the new, higher-temperature phase. This process, such as austenite formation in steel or solid-to-liquid melting, involves absorbing energy, while the starting transformation temperature shifts higher with faster heating rates.
Heating utility – It refers to an external resource stream, such as steam, hot oil, or flue gas, used to transfer heat to a process fluid, vessel, or space. These systems are necessary for maintaining, generating, or supplying heat in industrial plants.
Heating value – Heating value of a fuel is the quantity of heat released through complete combustion of a specified quantity of it. It is normally expressed in joules or kilo-calories per cubic metre The high heat values are conventionally measured with a bomb calorimeter. Low heat values are calculated from high heat value test-data.
Heating value specification – It defines the needed energy content of a fuel, normally expressed as ‘higher heating value’ (HHV) or ‘lower heating value’ (LHV) in units like mega-joules per kilogram, ensuring it meets performance standards for combustion, efficiency, and equipment design. It sets limits for energy density to optimize combustion, frequently accounting for fuel composition, moisture content, and incombustible gases (nitrogen, carbon di-oxide).
Heating, ventilation, and air conditioning (HVAC) – It refers to technology, equipment, and systems used to regulate environmental conditions in residential, commercial, and industrial spaces. It ensures thermal comfort and high indoor air quality (IAQ) by controlling temperature, humidity, air purity, and circulation.
Heating zone – It is the controlled area within an industrial furnace, process equipment, or building HVAC (heating, ventilation, and air conditioning) system where specific temperatures are maintained. These zones allow for uniform temperature, concentration, and heat transfer (conduction, convection, or radiation) to optimize energy efficiency and performance. In furnaces or manufacturing, a heating zone is a specific, monitored segment where thermal conditions (e.g., radiation heat transfer) are kept uniform to process materials.
Heat input – It is the quantity of electrical energy per unit length supplied by a welding arc to a work-piece, typically measured in Joules per millimeter. It is an important welding parameter, which influences the weld pool size, cooling rate, micro-structure, and mechanical properties like strength and distortion.
Heat integration – It is the systematic design and optimization of industrial processes to maximize energy efficiency by reusing heat. It involves matching hot process streams needing cooling with cold streams needing heating, mainly using heat exchanger networks (HENs) to minimize external utility consumption, reduce costs, and lower environmental impact.
Heat intensity – It normally refers to heat flux or thermal flux density. It is defined as the rate of heat energy transfer per unit area. It measures the concentration or ‘strength’ of thermal energy passing through a surface, acting as a vector quantity with magnitude and direction.
Heat island – These are areas such as buildings, roads, and other infrastructure which absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies. These pockets of heat are referred to as heat islands. Heat islands can form under a variety of conditions, including during the day or night, in small or large cities, in suburban areas, in northern or southern climates, and in any season.
Heat island effect – It is a dome of high temperatures over an industrial area caused by structural and different heat fluxes, and pollutant emissions.
Heat island intensity – It is defined as the measured numerical difference in temperature between a heat island area and its surrounding areas. It quantifies the magnitude of warmth, with intensities frequently ranging from 1 deg C to 10 deg C.
Heat island reduction – It refers to technical strategies designed to decrease elevated surface and air temperatures in urban areas compared to surrounding rural areas. This is achieved by increasing solar reflectivity (albedo) of surfaces, improving vegetation cover, and using, cool, permeable materials to mitigate heat absorption by infrastructure.
Heat kernel h (t, x, y) or k (t, x, y) – It is the fundamental solution to the heat equation, describing the evolution of temperature (or diffusion of heat / information) from a point source ‘y’ at time ‘t = 0’ to a point ‘x’ at time ‘t = above 0’. It represents the Green’s function for the heat operator on a domain, manifold, or network.
Heat leak – It is the unwanted, unintended transfer of thermal energy into a system (typically cryogenic or insulated) from its surroundings, caused by conduction, convection, or radiation. It represents an energy gain which increases the heat load on a cold system, frequently measured in watts.
Heat loss coefficient – It is a metric measuring the rate of thermal energy loss from a structure or system to its surroundings per unit of temperature difference, normally expressed in watts per kelvin or watts per deg C. It indicates total energy performance by combining transmission (U-values) and infiltration (air leakage) losses.
Heat loss in buildings – It is defined as the transfer of thermal energy from the interior of a structure to the external environment, influenced by factors such as ambient temperature differences, wind strength, and the thermal transmittance of building materials. It is calculated for different components, including windows, walls, and ventilation, to assess the efficiency of a building’s thermal performance.
Heat mark – It is the extremely shallow depression or groove in the surface of a plastic visible because of a sharply defined rim or a roughened surface.
Heat meter – It is also called thermal energy meter. It is a device which measures the thermal energy (in watts-hour) consumed or transferred in a heating / cooling system by calculating the product of the volume flow rate of a heat transfer fluid (normally water) and the temperature difference (dT) between the supply and return lines.
Heat metering – It is the process of measuring thermal energy consumption in HVAC (heating, ventilation, and air conditioning) or district heating systems, usually for billing, efficiency monitoring, and conservation. It quantifies heat transfer by measuring the fluid volume flow rate, the temperature difference (dT) between supply and return pipes, and the heat capacity of the transfer fluid.
Heat of fusion – It is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid, at constant pressure. The enthalpy of fusion is the amount of energy required to convert one mole of solid into liquid. For example, when melting 1 kilogram of ice (at 0 deg C under a wide range of pressures), 333.55 kilojoule of energy is absorbed with no temperature change.
Heat of solidification – It is the change in the enthalpy when a substance changes from liquid to solid. It is equal and opposite.
Heat of transport (Qi) – It is the quantity of heat energy carried by a unit mass of a component ‘i’ during isothermal diffusion, or the net heat flow associated with the diffusion of a component in the absence of a temperature gradient. It represents the energy difference between the moving particles and the surrounding matrix.
Heat of vapourization – It is also called heat of evaporation. It is the quantity of energy (enthalpy) which is to be added to a liquid substance to transform a quantity of that substance into a gas. The enthalpy of vapourization is a function of the pressure and temperature at which the transformation (vapourization or evaporation) takes place. The enthalpy of vapourization is frequently quoted for the normal boiling temperature of the substance. Although tabulated values are normally corrected to 298 Kelvin, that correction is frequently smaller than the uncertainty in the measured value. The heat of vapourization is temperature-dependent, though a constant heat of vapourization can be assumed for small temperature ranges. The heat of vapourization diminishes with increasing temperature and it vanishes completely at a certain point called the critical temperature. Above the critical temperature, the liquid and vapour phases are indistinguishable, and the substance is called a supercritical fluid.
Heat pipe – It is a passive, high-efficiency thermal transfer device that moves large quantities of heat between solid interfaces through latent heat of vapourization. It uses a sealed, evacuated tube containing a working fluid and a capillary wick structure to move heat from an evaporator to a condenser through phase change.
Heat pipe cooled reactor – It is a compact, solid-state nuclear reactor which uses passive, high-temperature heat pipes to transfer fission heat from the core to an energy conversion system, eliminating the need for traditional pumped coolant loops. It offers high reliability, inherent safety, and is mainly designed for space power, remote, or decentralized applications.
Heat pipe technology – It is a passive, high-efficiency heat transfer method using a sealed, evacuated pipe with an internal wick structure and working fluid to transport thermal energy through phase change (evaporation-condensation). It acts as a thermal super-conductor, transferring heat between solid interfaces with extremely high effective thermal conductivity, frequently hundreds of times faster than solid copper.
Heat pipe vacuum tube – It is a high-efficiency passive heat transfer device consisting of a sealed metal pipe (normally copper) containing a small quantity of working fluid and a wick structure, placed inside an evacuated glass tube to minimize heat loss. It uses phase-change (evaporation-condensation) to transfer heat from a solar-heated evaporator to a condenser with near-isothermal performance.
Heat pipe wall – It is a specialized building component or structural vessel designed for passive, high-efficiency thermal management. It consists of an evacuated tube lined with a porous wick structure and partially filled with a working fluid, enabling isothermal heat transfer through continuous evaporation and condensation cycles.
Heat production – It is the generation of thermal energy through the conversion of other energy forms (chemical, electrical, mechanical). It involves processes such as combustion, friction, or resistive heating (Joule heating), necessary for industrial applications like power generation, processing, and thermal management systems.
Heat pump – It is a system which transfers thermal energy from a low-temperature source (sink) to a high-temperature reservoir using external work (normally electricity). Operating on a reverse refrigeration cycle, it utilizes a refrigerant, compressor, condenser, and evaporator to provide efficient heating, cooling, or hot water for buildings.
Heat pump unit – It is a system designed to transfer thermal energy from a low-temperature source to a high-temperature sink, or vice versa, to provide heating, cooling, or domestic hot water. Operating on the refrigeration cycle, it utilizes a compressor, evaporator, condenser, and expansion valve to move heat rather than generate it, offering high energy efficiency.
Heat pump water heater – It is an energy-efficient appliance which utilizes an electric vapour-compression refrigeration cycle to transfer heat from surrounding air or water sources into a storage tank, rather than generating heat directly through electrical resistance. It acts like a refrigerator in reverse, using a compressor, evaporator, and condenser to heat water, achieving 60 % to 70 % higher efficiency than conventional electric heaters.
Heat radiation – It is also known as thermal radiation. It is the emission of electromagnetic energy (mostly infrared) from hot metals and furnace surfaces because of their high temperature, serving as a main, non-contact heat transfer method during smelting, heating, and cooling. It is important in furnaces where heat is transferred through radiation between surfaces, frequently governed by the Stefan-Boltzmann law.
Heat recovery – It consists of utilizing the waste heat exiting through the flues. Some forms of heat recovery are air preheating, fuel preheating, load preheating, recuperative, regenerative, and waste heat boilers.
Heat recovery boiler – It is also called waste heat recovery boiler. It is a system which captures thermal energy from high-temperature industrial exhaust gases (from turbines, engines, or furnaces) to produce steam or hot water without additional fuel. It increases efficiency by converting waste energy into useful process heat or power, typically utilizing finned tubes to maximize heat transfer.
Heat recovery steam generation – It is a system which combines different heat streams to utilize excess heat for electricity generation through steam turbines, using multiple steam pressure levels for improved efficiency.
Heat recovery steam generator (HRSG) – It is an energy recovery heat exchanger which recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. It produces steam which can be used in a process or used to drive a steam turbine. It is a high-efficiency steam boiler which uses hot gases from a gas turbine to generate steam in a thermodynamic Rankine cycle. This system is able to generate steam at different pressure levels as per the process requirements.
Heat recovery unit – It is a system which captures waste heat or energy (thermal mass) from a high-temperature exhaust air stream and transfers it to a lower-temperature intake air stream, or vice-versa, without mixing the airflows. Used to improve energy efficiency in HVAC (heating, ventilation, and air conditioning), it reduces heating / cooling loads and saves energy.
Heat recovery vapour generator – It is a sub-system which utilizes waste heat to produce steam or vapour, improving the efficiency of cogeneration systems by converting thermal energy into useful outputs such as heating or power.
Heat recovery ventilation – It is a mechanical ventilation system which supplies fresh, filtered outdoor air into a building while simultaneously exhausting an equal amount of stale indoor air, using a heat exchanger to transfer thermal energy between the two airstreams. It improves energy efficiency by recovering 60 % to 95 % of the heat from exhaust air, preheating (or precooling) incoming air to reduce HVAC (heating, ventilation, and air conditioning) energy consumption while managing indoor air quality.
Heat rejection – It is the process of transferring waste heat from a thermo-dynamic system, such as an HVAC (heating, ventilation, and air conditioning) unit, refrigerator, or engine), to the surrounding environment or a heat sink, allowing the system to maintain operational efficiency. It involves expelling heat through a condenser or cooling tower, frequently totaling the heat removed from a cool space plus the energy added by the compressor.
Heat release rate – It is the rate which describes the heat available per square metre of heat-absorbing surface in the furnace or per cubic metre of volume.
Heat removal factor – It is a dimensionless parameter in solar thermal engineering which represents the ratio of a collector’s actual useful energy gain to the maximum possible useful gain if the entire collector surface has been at the fluid inlet temperature. It measures heat transfer efficiency, indicating how effectively the heat transfer fluid removes energy from the absorber, typically ranging from 0 to 1.
Heat resistance – It is the property or ability of plastics and elastomers to resist the deteriorating effects of high temperatures.
Heat-resistant alloy – It is also known as super alloy. It is a material which shows extremely high creep strength and high temperature corrosion / oxidation resistance, making it suitable for applications demanding superior mechanical properties at high temperatures. Heat-resistant alloy has been developed for very-high-temperature service where relatively high stresses (tensile, thermal, vibratory, or shock) are encountered and where oxidation resistance is frequently needed.
Heat resistant cast irons – These cast irons combine resistance to high temperature oxidation and scaling with resistance to softening or micro-structural degradation. Resistance to scaling depends mainly on high alloy content, and resistance to softening depends on the initial micro-structure along with the stability of the carbon containing phase. Heat resistant cast irons are normally ferritic or austenitic as cast. Carbon exists predominantly as graphite, either in flake or nodular form, which subdivides heat resistant cast irons into either gray or ductile cast irons. There are also ferritic and austenitic white cast iron grades, although they are less frequently used.
Heat resistant conveyor belt – It is a thermo-stable conveyor belt which is used for transporting materials with temperatures of 60 deg C and higher. Damage to cover rubber varies depending on the temperature or shape of transported materials and it is critical to choose suitable belt materials depending on the use conditions. The relationship between the temperatures of the material and the belt surface is especially noteworthy. This is since cooling is mainly achieved on the return trip as the temperature of the belt surface is different from that of the material, although it varies depending on the material shape, belt length, speed, operation environment, and operating hours
Heat-resistant nickel alloys – These are frequently called nickel-based superalloys. These are metallic materials designed to maintain high mechanical strength, creep resistance, and oxidation / corrosion resistance at elevated temperatures, typically above 600 deg C. These alloys are important for power generation, and chemical processing, featuring alloying elements like chromium for oxidation resistance and titanium / aluminum for precipitation hardening.
Heat resistant steels – These steels are extensively used for high temperature components, and they cover a broad range of applications. The properties of steel and its yield strength considerably decrease as the steel absorbs heat when exposed to high temperatures. Heat resistance means that the steel is resistant to scaling at temperatures higher than 500 deg C. Heat resistant steels are meant for use at temperatures higher than 500 deg C since they have got good strength at this temperature and are particularly resistant to short-term and long-term exposures to hot gases and combustion products at temperature higher than 500 deg C. These steels are solid solution strengthened alloy steels. The heat-resistant steels are normally classified into ferritic / martensitic steels and austenitic steels. The ferritic / martensitic steels have the same body centered cubic (bcc) crystal structure as iron. They are simply iron containing with relatively small addition of alloying elements, such as the main element chromium added from 2 % to around 13 %. These ferritic / martensitic grades also have a small percentage of manganese, molybdenum, silicon, carbon and nitrogen, mostly included for their benefits in the precipitation strengthening and encouraging high temperature behaviour. Ferritic grades are normally used since they are economical because of their low content of alloying elements. They also have some resistance to oxidation at red heat, and which is in direct proportion to the chromium content.
Heat retention – It is the ability of a material, component, or system to store thermal energy and minimize its dissipation to the surrounding environment over time. It is achieved by reducing thermal conductivity, improving thermal insulation, or increasing thermal mass (heat capacity).
Heatric – It is a technology which combines etched plates and formed fins to create a ‘hybrid heat exchanger’ (H2X), which integrates advantages of printed circuit heat exchangers (PCHE) and finned tube heat exchangers (FPHE).
Heat sealing – It is a method of joining plastic films by simultaneous application of heat and pressure to areas in contact.
Heat-sealing adhesive – It is a thermo-plastic film adhesive which is melted between the adherend surfaces by heat application to one or both of the adjacent adherend surfaces.
Heat setting jointing material – It is also known as heat setting mortar or simply refractory mortar. It is a type of jointing material which hardens at high temperatures and contains a chemical bond and / or a ceramic bond.
Heat shield – It is a shield which is designed to protect an object from overheating by dissipating, reflecting, absorbing heat, or simply gradually burn and fall away from the part, pulling the excess heat with it. The term is very frequently used in reference to exhaust heat management and to systems for dissipation of heat because of friction.
Heat sink – It is a material which absorbs or transfers heat away from a critical element or part. It is also a structure intended to dissipate heat from an active device into the ambient environment.
Heat sink base – It is the foundational, flat, high-conductivity metal plate (normally aluminum or copper) which directly contacts a heat-generating component to absorb thermal energy. Acting as the main heat spreader, it reduces localized hot spots and conducts heat away from the source to attached fins for convective dissipation.
Heat source – It is normally defined as any system, device, or natural body which provides thermal energy to another system, typically by transferring heat from a hotter to a colder object. It is classified as a thermal energy reservoir which supplies heat without decreasing considerably its own temperature.
Heat source term – It is the expression representing the power density distribution of a heat source, which can be either a volume source or a surface source, depending on the mode of energy transfer (keyhole or conduction) to the material. It incorporates parameters which adjust for the fraction of energy effectively deposited into the material, reflecting the complex interaction between the heat source and the metal.
Heat stabilizer – It is a specialized additive incorporated into materials, very frequently polymers like polyvinyl chloride (PVC), to prevent or delay chemical breakdown (thermal degradation) when exposed to high temperatures during processing (such as extrusion or injection moulding) and during their subsequent service life. Without stabilizers, polymers subjected to heat can undergo de-hydro-chlorination, oxidation, chain scission, and cross-linking, leading to discoloration, brittleness, loss of mechanical strength, and premature failure.
Heat stable salts – These salts are amine-based ionic degradation products formed in alkanolamine gas treating units when strong acids (e.g., chloride, formate, acetate) react with the amine. These salts are ‘heat stable’ since they do not decompose in the regenerator, causing accumulation which reduces solvent capacity, causes severe corrosion, and promotes foaming.
Heat storage technology – It is also called thermal energy storage (TES). It comprises engineering systems which capture, store, and release thermal energy (heating or cooling) for later use, enabling improved energy efficiency, demand balancing, and renewable energy integration. These systems utilize varied materials, such as water, molten salt, or phase-change materials, to bridge the time gap between energy supply and demand, ranging from short-term (diurnal) to long-term (seasonal) applications.
Heat streak – It is a coloured band(s) parallel to the rolling direction which varies in both width and exact location along the length.
Heat stress – It refers to the total net thermal load on a system or person from environmental factors (temperature, humidity, radiation) and internal heat generation (metabolic work), which exceeds the capacity for heat dissipation. It is the combination of environmental heat and work rate which leads to increased bodily heat storage.
Heat supply – It refers to the intentional transfer of thermal energy from a source (such as a boiler, furnace, or heat exchanger) to a process, or system to meet specific heating or, in some cases, industrial process requirements. It is an important component of thermal engineering, involving the generation, distribution, and utilization of heat energy.
Heat tinting – It means colouration of a metal surface through oxidation by heating to reveal details of the micro-structure.
Heat-to-power ratio – In combined heat and power (CHP) or cogeneration systems, it is defined as the ratio of useful thermal energy (heat) produced to the electrical energy (power) generated. It is an important performance indicator used to match energy supply with the demand of a facility.
Heat tracing – It is the controlled application of heat to pipes, tanks, and equipment to compensate for heat loss, maintain process temperatures, or prevent freezing. It is a important ‘winterization’ or process maintenance technology used to ensure fluids remain at the needed viscosity for flow and to prevent the solidification, condensation, or separation of materials in metallurgical, chemical, and petrochemical plants.
Heat tracing system – It is a solution which applies heat directly to pipes, tanks, and instruments to prevent freezing or maintain needed process temperatures. It involves wrapping electrical cables or installing steam pipes along process equipment, covered with thermal insulation. Engineering includes thermal loss calculations, cable selection, and control systems.
Heat transfer – It is a discipline of thermal engineering which hat concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into different mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they frequently occur simultaneously in the same system.
Heat transfer analysis – It is the examination of different modes of heat transfer and their applications, utilizing the first law of thermodynamics to evaluate energy balance and calculate heat transfer rates in different scenarios.
Heat transfer, boundary conditions – These conditions define the thermal behaviour at the outer surface of a material (e.g., casting, billet, slab) to calculate heat transfer rates, temperature distributions, and cooling rates. These conditions are important since they dictate how heat is transferred between the solid metal and its surrounding environment, such as air, water, or a mould.
Heat transfer coefficient – It quantifies the rate at which heat transfers between a surface and a fluid because of the convection, or across a boundary between a fluid and a solid, per unit area and temperature difference. It essentially measures how effectively heat moves across a boundary. Heat transfer coefficient is very frequently used in the context of convective heat transfer, where heat is exchanged between a surface and a moving fluid (either liquid or gas).
Heat transfer area – It is the total, effective physical boundary or interface surface through which thermal energy is exchanged between two systems (e.g., fluid-to-fluid) or surfaces, measured in square meter. It is a critical parameter in the heat transfer rate equation, where larger surface areas increase the total heat exchange rate. It is the surface area available for conduction, convection, or radiation, such as the outer surface area of tubes in a shell-and-tube heat exchanger.
Heat transfer coefficient (h) – It is a parameter representing the rate of heat transfer per unit surface area per unit temperature difference between a solid surface and a surrounding fluid (q” = h x dt). Measured in watts per square meter kelvin, it quantifies the effectiveness of convection, combining fluid velocity, viscosity, and thermal properties.
Heat-transfer-coefficient curve – It plots the efficiency of heat removal from a metal surface against surface temperature, typically displaying a, frequently non-linear, rise and fall because of the phase changes in the cooling medium (e.g., vapour film to boiling to convection). It defines the rate of heat flux (q divided by the temperature difference between the hot metal (Tw) and the coolant (Tf), as expressed by ‘q = h(Tw-Tf)’.
Heat transfer considerations – These refer to the systematic analysis and management of thermal energy movement (conduction, convection, and radiation) during the extraction, refining, casting, and heat treatment of metals. These considerations are necessary to ensure structural integrity, achieve desired mechanical properties, and maximize energy efficiency in processes like blast furnaces, rolling, and quenching.
Heat transfer effect – It refers to the transfer of thermal energy between systems or their surroundings, which can occur through conduction, convection, and radiation, and is important in different engineering applications to manage temperature in systems such as buildings, electrical equipment, and power plants.
Heat transfer enhancement – It is also called heat transfer augmentation. It is the process of improving the rate of heat transfer, increasing the heat transfer coefficient, or reducing the size / cost of heat exchange equipment. It involves boosting thermal performance without considerably changing the overall system, typically achieved by improving surface area, creating turbulence, or generating secondary flows in the fluid.
Heat transfer equipment – It refers to engineered devices designed to facilitate the transfer of thermal energy between two or more fluids (liquids or gases) at different temperatures, or between a solid surface and a fluid, without needing direct mixing. These systems, including heat exchangers, boilers, and condensers, optimize energy efficiency and manage temperature in industrial applications.
Heat transfer factor – It is that portion of the heat transfer equations which relates to the cellular structure.
Heat transfer fluid – It is a gas or liquid, such as water, glycol, or oil, used to transport thermal energy between systems for heating or cooling. It acts as an intermediary, circulating in closed systems to remove heat (cooling) or provide heat (heating) to industrial processes, ensuring thermal stability and operational efficiency.
Heat-transfer intensification – It refers to techniques designed to increase the rate of heat exchange during heating or cooling processes, reducing equipment size and energy consumption. It involves optimizing thermal performance in quenching, annealing, or melting operations, frequently by using turbulent flow, extended surfaces (fins), or advanced coolants to improve efficiency.
Heat transfer medium – It is a solid, liquid, or gas used to transport, store, or exchange thermal energy within a system. These media operate by absorbing heat from a high-temperature source and releasing it to a lower-temperature sink, important for applications like refrigeration, process heating, and cooling.
Heat transfer model – It is a mathematical or numerical framework which simulates the exchange of thermal energy (conduction, convection, radiation) between systems. These models, frequently implemented in CAD (computer-aided design) or CFD (computational fluid dynamics) software, solve governing differential equations to predict temperature distributions, heat flux, and phase changes, optimizing performance for applications like heat exchangers, electronics cooling, and insulation.
Heat-transfer module – It is a specialized software tool which used to model the movement of thermal energy through conduction, convection, and radiation. These modules simulate heat transfer in solids and fluids, including heat conduction equations, boundary / interface conditions, and coupling temperature fields to fluid domains. These modules can model phase changes (melting / solidification) in thermal storage units, with applications in optimizing thermal management for electronics and photovoltaics.
Heat transfer phenomena – These phenomena refer to the exchange of thermal energy between systems because of the temperature differences, which can occur through conduction, convection, and radiation. These phenomena are important in different applications, including heat exchangers, air conditioning, and material processing.
Heat-transfer rate – It is the quantity of thermal energy (joules) transferred per unit time (seconds), measured in watts or joules per second, driven by temperature differences across metal components. It quantifies how fast heat moves during processes like casting, quenching, or annealing, influenced by surface area, thermal conductivity, and the material’s thickness. The rate of heat flow through a material, is important for determining heating / cooling efficiency and material properties.
Heat transfer resistance – It refers to the total thermal resistance in a heat transfer process, characterized by the sum of convective resistances for hot and cold fluids and the conductive resistance of the partition, and is the inverse of the overall heat transfer coefficient scaled by the surface area.
Heat transfer surface – It is the physical boundary or interface, such as a tube wall or plate, through which thermal energy flows between two mediums (fluids or solids) through conduction, convection, or radiation. It is engineered to maximize or control heat exchange efficiency in systems like heat exchangers, boilers, and radiators.
Heat transfer theory – It is the physical process governing the transfer of thermal energy through conduction, radiation, and convection, which is necessary for predicting temperatures and understanding the factors influencing it.
Heat transformation – It refers to the strategic process of converting, managing, or moving thermal energy (heat) from one form or location to another to perform work, such as converting solar heat directly into cooling through sorption refrigeration. It focuses on improving energy efficiency, frequently using thermal energy to drive systems rather than mechanical or electrical energy.
Heat transmission – It is the process of thermal energy exchange between physical systems, materials, or environments because of the temperature differences, typically moving from high to low temperature. It is a fundamental discipline of thermal engineering governed by the second law of thermodynamics, encompassing conduction, convection, and radiation.
Heat transport – It is the process of moving thermal energy from one location to another because of a temperature difference, important for regulating system temperatures. It involves three main mechanisms, conduction (solid contact), convection (fluid movement), and radiation (electro-magnetic waves, to design efficient cooling, heating, and energy systems.
Heat transport capability – It is the maximum rate at which a system (e.g., heat pipe, loop) can transfer thermal energy from a source to a sink. It defines the efficiency, capacity, and limits, such as viscous, sonic, or capillary limits, of systems designed to manage, move, or remove heat.
Heat trap – It is a plumbing configuration, typically a U-shaped pipe loop or check valve installed on the inlet and outlet of a water heater, designed to prevent standby heat loss. It creates a convective, thermal, or mechanical seal which stops hot water from rising into pipes and cooling down when the heater is inactive, improving overall energy efficiency. In atmosphere, green-house gases (GHGs) such as carbon di-oxide, nitrous oxide and methane, trap heat and energy, hence preventing solar radiation from escaping back into space. As the quantity of greenhouse gases in the atmosphere increases so does the trapped heat and corresponding global temperature.
Heat treatable alloy – It is an alloy which can be strengthened through heat treatment processes, frequently involving the formation of metastable coherent phases, such as the beta phases of Mg2Si in aluminum alloys. These modifications improve the mechanical properties of the alloy, making it suitable for several applications.
Heat treatable aluminum alloy – For this type of alloy, the major, and perhaps some minor, alloying elements do provide substantial solid solution and precipitation strengthening during solution heat treatment and subsequent aging. These alloys are referred to as heat treatable.
Heat treating – It is a controlled process of heating and cooling metals or alloys in their solid state to deliberately alter their physical and mechanical properties, such as hardness, strength, toughness, and ductility, without changing the part’s shape. It involves three main steps namely heating to a specific temperature, soaking (holding) at that temperature, and cooling at a controlled rate. It is a term used to cover annealing, hardening, tempering, and so on.
Heat treating film – It is a thin coating or film, normally an oxide, formed on the surface of a metal during heat treatment.
Heat-treating furnaces – These furnaces are normally classified in two broad categories, batch furnaces and continuous furnaces. In batch furnaces, work-pieces normally are manually loaded and unloaded into and out of the furnace chamber. On the other hand, a continuous furnace has an automatic conveying system which provides a constant work load through the unit.
Heat treating of aluminum alloys – It is a metallurgical process involving controlled heating, soaking, and cooling to improve mechanical properties, mainly strength and hardness, through precipitation hardening (age hardening). It transforms unstable, supersaturated solid solutions into stable micro-structures, typically involving solution heat treatment, quenching, annealing, and aging for aluminum-copper, aluminum-magnesium-silicon, aluminum-zinc-magnesium, and aluminum-lithium systems.
Heat treating of copper alloys – It is a metallurgical process involving controlled heating, soaking, and cooling to alter micro-structures and improve mechanical properties like strength, hardness, and ductility. Key processes include annealing (softening), stress relieving, solution treatment, and precipitation hardening (age hardening).
Heat treating of nickel alloys – It is a metallurgical process involving controlled heating, soaking, and cooling to manipulate microstructure, typically maintaining an austenitic face-centered cubic (fcc) lattice, to improve mechanical strength, ductility, and corrosion resistance. Key techniques include solution annealing to soften / homogenize and aging (precipitation hardening) to increase strength through phases like (gamma prime).
Heat treating of stainless steel – It is a metallurgical process involving controlled heating (normally above 1,000 deg C) and cooling to modify microstructure, increase corrosion resistance, relieve stress, and adjust mechanical properties like hardness or ductility. It transforms the internal structure (e.g., martensite formation) without melting, frequently in a vacuum or inert atmosphere to prevent scaling Different types of stainless-steel need specific heat treatments based on their crystalline structure. These include (i) solution annealing (austenitic and duplex), (ii) hardening and tempering (martensitic), and (Iii) stress relieving.
Heat treating of steel – It is a metallurgical process involving controlled heating, holding (soaking), and cooling of solid-state steel to intentionally alter its micro-structure, physical, and mechanical properties. It increases strength, hardness, toughness, or ductility to suit specific engineering applications. The three-stage process includes heating, soaking, and cooling.
Heat treating of superalloys – It is a precise metallurgical process involving controlled heating, soaking, and cooling (often in a vacuum with inert gas quenching) to manipulate microstructure, improve high-temperature creep / fatigue strength, and optimize corrosion resistance. It typically involves solution treatment to dissolve phases, followed by aging to precipitate strengthening phases like gamma prime.
Heat treating processes – All the heat-treating processes consist of subjecting the steel to a definite time-temperature cycle. This time-temperature cycle has three components namely (i) heating, (ii) -holding at particular temperature range (soaking), and (iii) cooling. Individual cases can differ, but certain fundamental objectives are there.
Heat treat lot – It is the material of the same mill form, alloy, temper, section, and size traceable to one heat treat furnace load (or extrusion charge or billet in the case of press heat treated extrusions) or, if heat treated in a continuous furnace, charged consecutively during an 8-hour period.
Heat treatment – It consists of heating and cooling a solid metal or alloy in such a way as to get desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.
Heat treatment charts – These are furnace charts providing a temperature against time record of the heating and cooling cycle needed by a specific heat treatment process for a particular furnace load of steel or steel parts.
Heat treatment conditions – These conditions refer to the specific parameters applied during the heat treatment process of materials, including austenitization temperature, cooling rate, and tempering temperature, which considerably influence the mechanical properties such as toughness and hardness of the material.
Heat treatment of aluminum and its alloys – It consists of the thermal processing of a work-piece specifically to alter its mechanical properties. It includes (i) annealing to soften and improve ductility, (ii) solution treatment and precipitation hardening to increase strength, and (iii) homogenization. The structure of as cast semi-finished products e.g., slab, extrusion billet or forging blanks is invariably chemically segregated, that is, the alloying elements are concentrated locally rather than uniformly distributed within the microstructure. Homogenizing is a way of mitigating this as the work-piece is held at a suitably high temperature for sufficient time to eliminate, or at least decrease, chemical segregation by diffusion of the alloying elements. The heat treatment process does not include heating before hot rolling, forging, or extrusion etc.
Heat treatment of copper and its alloys – A range of heat treatment processes are applied to copper and it alloys which includes (i) homogenizing, (ii) annealing, (iii) stress relieving, (iv) solution treatment and ageing, and (v) quench and temper hardening. It is important to recognize that not all processes are appropriate for all the alloys. Homogenizing in which prolonged soaking at high temperature is used to reduce solidification chemical segregation in castings particularly in phosphor bronzes, copper nickels and silicon bronzes which have long freezing ranges. Annealing is used to soften and increase ductility and toughness in wrought alloys. Stress relieving is used to relieve internal stresses without considerably affecting mechanical properties. Solution treatment and ageing is used on beryllium copper, copper / chromium, copper / zirconium, and copper / nickel / silicon / chromium alloys to increase mechanical properties. Quench and temper hardening is applied to certain aluminum bronzes, nickel aluminum bronzes, and some cast manganese bronzes to increase their mechanical properties.
Heat treatment parameters – These are the precise, controlled conditions, specifically temperature, time (soaking), and cooling rates, applied to materials (like steel) to alter their microstructure and achieve desired mechanical properties. These, along with heating rates and atmospheres, define the cycle necessary to improve properties like hardness, ductility, or toughness.
Heat treatment process – It is a process involving controlled heating, holding, and cooling of metals or alloys in their solid state to deliberately alter their physical, mechanical, and microstructural properties without changing their shape. It aims to improve characteristics like hardness, ductility, toughness, and wear resistance.
Heat treatment solution – It is a treatment in which an alloy is heated to a suitable temperature and held at this temperature for a sufficient length of time to allow a desired constituent to enter into solid solution, followed by rapid cooling to hold the constituent in solution. The material is then in a super-saturated unstable state which may subsequently exhibit age hardening.
Heat treatment verification – It is the essential process of validating that a metal component has achieved its needed metallurgical structure and mechanical properties (such as hardness, tensile strength, and ductility) after a controlled heating and cooling process. It ensures the integrity of the heat treatment, frequently involving testing for proper microstructure, case depth, or hardness to confirm the part’s performance.
Heat treat stain – It is a discolouration because of the non-uniform oxidation of the metal surface during solution heat treatment.
Heat-up path – It is also called heating curve. It is a predefined, controlled, and time-dependent schedule of temperature increases applied to a system, component, or material to reach a specific operating temperature without damaging it. This is critical in industries dealing with thick-walled pressure vessels, turbines, or during welding, where uneven heating can cause thermal fatigue, cracking, or catastrophic failure.
Heat-wave – It describes a period of extremely hot weather. There is no uniform definition for heat-wave. The temperature threshold at a specific percentile (e.g. 90 %, 95 %) lasting for several days is also applicable for analyzing people’s adaptability. Under global warming, heatwaves are increasingly frequent and intense.
Heave force – It is the vertical upward force exerted on a structure or vessel, causing it to rise. It normally refers to two distinct phenomena: vertical, oscillatory wave-induced forces on marine platforms / vessels or upward pressure exerted on foundations by expansive, frost-sensitive, or saturated soils.
Heave motion – It refers to the vertical (up-and-down) linear displacement of a floating vessel, platform, or structure along its Z-axis, mainly caused by ocean wave forces. It is one of the six degrees of freedom in marine hydrodynamics, crucial for designing stable offshore systems, managing vessel seakeeping, and implementing motion compensation to ensure operational safety in harsh environments.
Heave plate – It is a submerged, frequently circular or polygonal, structural component attached to floating offshore platforms (like Spars, semi-submersibles, or wave energy converters) to reduce vertical movement (heave motion). It improves stability by increasing added mass and viscous damping, which shifts the natural period away from wave energy frequencies.
Heave response – It refers to the vertical, up-and-down oscillatory motion of a floating structure, such as a ship or platform, induced by ocean waves. It is a critical, single-degree-of-freedom motion defined by the vessel’s vertical displacement (z) over time, influenced by hull geometry, damping, and added mass.
Heaviside step function – It is a discontinuous function important for modeling switches, impulsive forces, and sudden changes. It is defined as 0 for negative time (t is below zero) and 1 for positive time (t is above zero). It represents a signal which switches on at a specific time and stays on indefinitely.
Heavy damping – It is also called overdamping. It occurs when a system’s damping coefficient is higher than its critical damping, forcing it to return to equilibrium slowly without oscillating. It provides a sluggish, non-oscillatory response, taking longer to settle than critical damping, normally used in door closers.
Heavy-duty – It means designed to withstand great strain, and hard usage without break-down. Heavy duty machinery provides an unusual amount of power and durability.
Heavy-duty crane – It is defined by its ability to lift substantial loads and withstand rigorous, continuous operation in demanding industrial environments. These cranes are built with robust components and mechanisms to handle heavy materials and equipment with precision and reliability. Capacity ranges for heavy-duty cranes can vary widely, from 5 tons to over 1,000 tons, depending on the type of crane and its application.
Heavy-duty oil – It is an oil which is stable against oxidation, protects bearings from corrosion, and has detergent and dispersant properties. Heavy-duty oils are suitable for use in gasoline and diesel engines.
Heavy elements – These are normally defined as elements with an atomic number higher than 92 (uranium), frequently produced artificially through particle accelerators or nuclear reactors. These are distinct from ‘super-heavy’ elements (atomic number higher or equal to 112 or 114) and differ from ‘heavy metals’ (high density / toxicity, e.g., lead, mercury).
Heavy equipment – It refers to heavy-duty vehicles specially designed to execute construction tasks, very frequently involving earthwork operations or other large construction tasks. Heavy equipment normally comprises five equipment systems namely the implement, traction, structure, power train, and control / information. Heavy equipment functions through the mechanical advantage of a simple machine which multiplies the ratio between input force applied and force exerted, easing and speeding tasks which frequently can otherwise take hundreds of people and several weeks’ labour. Some such equipment uses hydraulic drives as a primary source of motion.
Heavy fuel – It is a type of fuel derived from the residuals of crude oil refining, typically characterized by high viscosity and lower quality because of the inclusion of cracked residuums and undesirable constituents like sulphur and metals. Heavy fuels are normally used in marine diesel engines after being blended and reformulated to meet performance specifications.
Heavy fuel oil – It is a category of fuel oils of a tar-like consistency. It is also known as bunker fuel, or residual fuel oil. This oil is the result or remnant from the distillation and cracking process of petroleum.
Heavy gas oil – It is a high-boiling, viscous petroleum fraction derived from vacuum distillation or cracking processes, typically boiling above 350 deg C. It is mainly used as feedstock for catalytic cracking units or blended into industrial fuel oils. It is characterized by high density, high viscosity, and a lower hydrogen-to-carbon ratio.
Heavy hydro-carbon content – It defines the proportion of complex, high-molecular-weight compounds (typically above C12 or C6+ depending on context) in a hydrocarbon mixture. These, including resins and asphaltenes, are characterized by high viscosity, lower volatility, and higher density, often resulting in heavy oil / bitumen, below 20-degree API (American Petroleum Institute), or condensed liquids in gas processing.
Heavy hydro-carbons – These are high-molecular-weight compounds (mainly alkylated cyclics, resins, and asphaltenes) with high boiling points, typically above 550 deg C, high density, and high viscosity. They represent fractions which cannot be distilled under atmospheric / vacuum distillation, appearing as residues, bitumen, or asphalt. They are distinguished from light ends by lower API (American Petroleum Institute) gravity (below 20-degree) and higher viscosity.
Heavy lift vessel – It is a vessel with a specific crane that has a large lifting capacity of up to thousands of tons.
Heavy media separation – Heavy media separation devices has been developed as a more effective alternative to jigging for the upgrading of the iron ores. Heavy media separation processes operate on the sink and float principle. A suspension of fine (minus 200 mesh) ferro-silicon in water is used to create a fluid media with a specific gravity of around 3. Silica rich particles with a specific gravity of about 2.6 float on the surface of such a medium while the denser and heavier iron ore particles with a specific gravity over 4 settles to the bottom. The conventional medium for concentrating coarse ore is ferro-silicon containing 15 % silicon and 85 % iron. Water suspensions containing 64 % to 85 % of finely ground ferro-silicon have specific gravities ranging from 2.2 to 3.6. The separation vessels for coarse ore (plus 9 millimeters) are normally spiral classifiers, rake classifiers or rotating drums. Ore finer than 9 millimeters and coarser than 3 millimeters can be separated in heavy media cyclones where the high gravitational forces accelerate the settling of the heavy iron ore particles. Finely ground magnetite is used to make up the heavy media for the cyclone separators rather than ferro-silicon. The dynamics of the cyclone create the density and media fluidity needed despite the lower specific gravity of the magnetite. Further the cost of magnetite is much less than ground ferro-silicon. The medium, ferro-silicon and magnetite, is washed from the sink and float products on fine screens equipped with wash troughs and water sprays and is recovered from the wash water with magnetic separators and recycled.
Heavy metal biosorption – It is an eco-friendly, passive physicochemical engineering process which uses inactive or live biomass (bacteria, fungi, algae, or plant materials) to remove toxic metal ions (lead, cadmium, nickel, zinc, mercury, copper) from aqueous solutions. It utilizes mechanisms like ion exchange, adsorption, and surface complexation, offering a cost-effective alternative for industrial wastewater treatment.
Heavy metal, Heavy alloy – It is a sintered tungsten alloy with nickel, copper, and / or iron, the tungsten content being at least 90 % and the density being at least 16.8 grams per cubic centimeter.
Heavy metal ions – These are positively charged, high-density metallic elements (typically above 5 grams per cubic centimeter or atomic number above 20) which, even at low concentrations, pose environmental and health risks due to their non-biodegradable nature, persistent accumulation in water / soil, and toxicity. Common examples include Pb2+ (lead), Hg2+ (mercury), Cd2+ (cadmium), Cr6+ (chromium), As3+ (arsenic), Ni2+ (nickel).and Cu2+ (copper).
Heavy metal retention – It refers to the mechanisms (adsorption, ion exchange, precipitation, and complexation) by which solid media (soil, sediments, engineered materials) hold, trap, or immobilize heavy metals, preventing their migration into the environment. It measures the capacity to reduce bio-availability and mobility of contaminants.
Heavy metals – This term refers to a group of toxic metals including arsenic, chromium, copper, lead, mercury, silver, and zinc. Heavy metals frequently are present at industrial sites where operations have included battery recycling and metal plating.
Heavy mineral sands – These refer to minerals with a specific gravity higher than 2.85, including zircon, monazite, rutile, ilmenite, and garnet, which are mainly extracted from beach sand mining and increasingly from undersea deposits to meet industrial demands.
Heavy naphtha – It is an important, high-boiling petroleum refinery stream, typically boiling between 90 deg C and 200 deg C and consisting of hydrocarbons with 6 to 12 carbon atoms. It is mainly used as feedstock for catalytic reformers to produce high-octane gasoline components (aromatics) and in the petrochemical industry, as opposed to lighter, lower-boiling naphtha.
Heavy oil – It is a highly viscous, dense form of crude oil which does not flow easily at reservoir temperatures, characterized by an API (American Petroleum Institute) gravity of below 20-degree and high viscosity, frequently over 100 mega-Pascal.second. It needs improved recovery techniques, such as thermal stimulation (e.g., steam injection), solvent injection, or mining, because of its high density, high sulphur content, and heavy molecular composition.
Heavy oil production – It refers to the extraction of highly viscous (over 100 mega-Pascal.second) and dense, API (American Petroleum Institute) gravity of below 20-degree, petroleum which does not easily flow under normal reservoir conditions. It needs specialized, energy-intensive techniques, mainly thermal methods like SAGD (steam-assisted gravity drainage), steam flooding, or cyclic steam stimulation (huff-n-puff), to reduce viscosity and improve flow, alongside cold production techniques.
Heavy rare earth elements – These are a subset of the lanthanide series (atomic numbers 63 to 71, Europium to Lutetium), plus Yttrium, defined by higher atomic weights, lower crustal abundance, and increased scarcity compared to light rare earths. Critically used for high-temperature permanent magnets, defense technologies, and electronics, they improve thermal stability and magnetic performance.
Heavy section mill – It is also called heavy structural mill. It is a type of rolling mill which designed to produce structural steel sections like beams, channels, angles, and other shapes with substantial dimensions. These mills are capable of handling blooms or ingots and shaping them into the desired profiles, frequently used for construction and infrastructure projects.
Heavy species – It refers to the constituents of plasma which include positive and negative ions, atoms, and excited or non-excited molecules, which are characterized by their higher mass compared to ‘light’ species such as electrons and photons.
Heavy structural shapes – It is a general term given to rolled flanged sections which have at least one dimension of their cross sections 80 millimeters or higher. The category includes beams, channels, tees and zees if the depth dimension is 80 millimeters or higher, and angles if the length of the leg is 80 millimeters or higher.
Heavy-tailed noise – It refers to probability distributions of noise (measurement, process, or gradient) which show a higher likelihood of extreme values (outliers) compared to Gaussian distributions, typically following a power-law decay rather than an exponential one. It is characterized by heavy tails and potentially infinite variance, considerably impacting state estimation, control system performance, and stochastic optimization.
Heavy vacuum oil – It is frequently referred to as ‘heavy vacuum gas oil’ (HVGO). It is an intermediate, high-boiling, high-viscosity petroleum fraction produced from the vacuum distillation of atmospheric residue. It is a critical feedstock in oil refineries, typically processed further to create high-value products like gasoline, diesel, and lubricants.
Heavy vehicle – It is normally a motor vehicle with a ‘gross vehicle mass’ (GVM) or aggregate trailer mass’ (ATM) exceeding 3.5 tons to 4.5 tons. These vehicles are engineered for heavy-duty freight, specialized construction, or passenger transport, needing robust frames, high-torque engines, and specific braking systems to manage substantial mass.
Heavy water – It is the water which is enriched to contain significantly more than the natural proportions (one in 6,500) of heavy hydrogen (deuterium, D) atoms to ordinary hydrogen atoms. Heavy water, effective in slowing neutrons down and having a low probability of absorbing neutrons, is used as a moderator in some reactor designs.
Heavy water reactors – These reactors use deuterium oxide (D2O) as both moderator and coolant, enabling the use of natural, unenriched uranium fuel. Engineered for high neutron economy, they typically utilize a pressure tube design to maintain high-pressure, high-temperature coolant without needing a large pressure vessel.
Hedging – It is taking a buy or sell position in a futures market opposite to a position held in the cash market to minimize the risk of financial loss from an adverse price change.
Heel – It is the surface on which a single-point tool rests when held in a tool post. In steelmaking, it means molten steel from a previous heat which has been retained for the nest heat to assist melting.
Heel block – It is a block or plate normally mounted on or attached to a lower die in a forming or forging press which serves to prevent or minimize the deflection of punches or cams.
Heel guide – It is also known as a heel block or heel plate. In a die set, it is a precision-machined, heavy-duty guiding component used in medium-to-large stamping and forming dies to align the upper and lower die shoes, especially when high lateral shear forces are present. Unlike traditional cylindrical guide posts, heel guides provide a robust, flat, or angled surface that prevents the upper die from shifting laterally relative to the lower die, ensuring the stamping clearance (die gap) remains consistent throughout the service life.
Height – It is the vertical measurement of an object, component, or structure, extending from a specified base level, datum, or reference point to its highest point. It represents the vertical dimension (distance or extent) important for design, safety, structural analysis, and, in geodetic surveying, the measurement along a perpendicular to a reference ellipsoid.
Height above ground level – It is a height which is measured with respect to the underlying ground surface.
Height above mean sea level – It is a measure of a location’s vertical distance (height, elevation, or altitude) in reference to a vertical datum based on a historic mean sea level.
Height between bottom of large bell and top of hopper – It is the vertical distance between bottom of the large bell closed and the intersection of the hopper or the hopper extension with the gas seal.
Height of bosh – It is the vertical distance between the hearth and bosh line.
Height distribution – It refers to the statistical representation of vertical measurements (such as surface roughness, wave heights, or particle sizes) within a population, typically characterized by parameters like mean height, standard deviation, or root mean square (RMS) height. It describes how varied heights are distributed across a surface or within a sample.
Height equivalent to a theoretical plate (H) – It is an important metric in separation processes (distillation, chromatography, absorption) defined as the column length (L) divided by the number of theoretical plates (N), expressed as ‘H = L/N’. It represents the height of packing needed to achieve one, equilibrium separation stage. Lower height equivalent to a theoretical plate indicates higher efficiency.
Height of hearth – It is the vertical distance between the hearth line and the centre-line of the tap hole. The latter is determined by the centre of the tap hole opening in the hearth jacket.
Height of in-wall – It is the vertical distance between the bottom in-wall line and the bend line.
Height of large bell hopper – It is the vertical distance between the inner large bell seat and the inter-section of the hopper or hopper extension with the gas seal.
Heisenberg box – it is a rectangle in the time-frequency plane which represents the time-frequency resolution of a function, with its area constrained by the Heisenberg uncertainty principle to be at least one-half, thereby limiting the joint resolution in time and frequency.
Heisenberg’s indeterminacy (uncertainty) principle – it states that the position (dp) and momentum (dm) of a particle cannot be simultaneously measured with arbitrary precision. It sets a fundamental limit, ‘dp x dm is higher than or equal to h/2’ (where ‘h’ is reduced Planck’s constant), meaning higher precision in measuring position forces higher uncertainty in momentum, and vice versa.
Helical baffles – These are specialized quadrant-shaped plates arranged at angles to the tube axis in shell-and-tube heat exchangers, forcing shell-side fluid into a continuous helical (spiral) flow path. They improve efficiency by reducing dead zones, lowering pressure drop, and providing continuous tube support, making them superior to traditional segmental baffles for reducing vibration and fouling.
Helical dies – These are specialized, high-precision tools with an internal or external helical (screw-like) profile used to shape metal components, very frequently for manufacturing helical gears or spiral tubes. They are designed to plastically deform materials into shapes which have teeth or features following a twist. These dies are frequently used in powder metallurgy (PM) for compaction or in extrusion processes.
Helical drilling – It is a high-precision manufacturing process used to create precise, high-quality, and frequently deep micro-holes by rotating a pulsed laser beam in a spiral path through the material. Unlike single-pulse drilling, this layer-by-layer material ablation minimizes the recast layer, reduces surface roughness, and enables complex geometries.
Helical gearing – It uses cylindrical gears with teeth cut at an angle (helix angle) to the axis of rotation, rather than parallel to it. This design ensures gradual engagement, resulting in smoother, quieter operation and higher load-carrying capacity than spur gears. Normally used for parallel shafts, they generate axial thrust
Helical gears – These gears differ from spur gears in that helical teeth are cut across the gear face at an angle rather than straight. Hence, the contact line of the meshing teeth progresses across the face from the tip at one end to the root of the other, reducing the noise and vibration characteristic of spur gears. Also, several teeth are in contact at any one time, producing a more gradual loading of the teeth which reduces wear substantially. The increased quantity of sliding action between helical gear teeth, however, places higher demands on the lubricant to prevent metal-to-metal contact and resulting premature gear failure. Also, since the teeth mesh at an angle, a side thrust load is produced along each gear shaft. Hence, thrust bearings are to be used to absorb this load so that the gears are held in proper alignment.
Helical gear teeth – These are inclined at an angle (helix angle) relative to the axis of rotation, rather than being parallel as in spur gears. This angled, screw-like design ensures gradual engagement, resulting in smoother, quieter operation, higher load capacity, and more continuous contact, though they generate axial thrust.
Helical ribs – These are spiral-shaped ridges or protrusions on a surface, normally applied internally in tubes to improve heat transfer by increasing flow turbulence and vortex generation, or on structural components (like reinforcement bar) to improve bonding and strength. They are designed to disrupt the boundary layer, improving fluid mixing and increasing the heat transfer coefficient.
Helical rolling mill – It is a type of metal forming process where a work-piece is shaped by passing it between rotating rolls which are angled to create a helical or spiral motion. This contrasts with traditional rolling, where rolls are typically aligned perpendicular to the work-piece’s movement. Helical rolling is particularly useful for producing axisymmetric parts with complex shapes, such as ball studs. These rolling mills utilize rolls with angled or helical grooves that impart both rotational and translational motion to the workpiece. The angled rolls cause the workpiece to move both around its axis and along its length, resulting in a helical pattern of deformation.
Helical screw thread – It is a continuous, uniform ridge or groove with a specific cross-sectional shape (e.g., V-shape, square) which winds helically around the exterior or interior surface of a cylinder or cone. It converts rotational torque into linear movement or force for fastening, adjusting, or power transmission.
Helical segment – It refers to a discrete portion or component which follows a spiral (helical) path, typically wrapping around an axis at a constant radius, pitch, and angle. It is a foundational concept in mechanical design, representing a section of a larger helical system, such as gear teeth, springs, or screw threads.
Helical spring – It is a mechanical device made of a wire coiled in the shape of a helix. It is formed by winding a wire or coil into a helical (spiral) shape. It is typically made from materials with high elasticity and tensile strength, such as steel, stainless steel, and beryllium copper. It is used to store energy, absorb shock, or maintain a force between contacting surfaces. It is designed to store energy elastically, meaning they can be compressed or stretched and then return to their original shape when the load is removed. Helical springs are widely used in different applications, such as for shock absorption, for energy storage, and for force application. Types of helical springs are compression springs, tension springs, and (ii) torsion springs.
Helical structure – It is a 3D, spiral-shaped component characterized by a continuous curve wrapped around a cylinder or cone at a constant angle, defined by its axis, radius, and pitch (lead). It translates rotational motion into linear movement or provides structural support, normally found in threads, springs, and piles.
Helical winding – In filament-wound items, a winding in which a filament band advances along a helical path, not necessarily at a constant angle, except in the case of a cylinder.
Helico-axial centrifugal pump – It is a multi-phase pump. It is a rotodynamic pump with one single shaft that requires two mechanical seals, this pump uses an open-type axial impeller. It is frequently called a Poseidon pump, and can be described as a cross between an axial compressor and a centrifugal pump.
Helicoidal surface – It is the surface generated by a line rotating at a uniform angular velocity around a fixed axis while simultaneously moving along that axis, with the pitch being the distance traveled along the axis during one complete revolution.
Heliostat – It is a device, mainly used in concentrating solar power (CSP) towers, consisting of a computer-controlled reflective mirror which tracks the sun on two axes. By adjusting its orientation, it maintains a perpendicular angle to the sun-receiver bisector, consistently reflecting solar radiation onto a stationary central receiver.
Helium (He) – It is a colourless, odourless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest after hydrogen. Liquid helium is used in cryogenics (its largest single use), and in the cooling of super-conducting magnets, with its main commercial application in magnetic resonance imaging (MRI) scanners. Helium’s other industrial uses are as a pressurizing and purge gas, as a protective atmosphere for arc welding, and in processes such as growing crystals to make silicon wafers.
Helium Brayton cycle – It is a closed-loop thermodynamic power cycle using helium as the working fluid in gas turbine systems, frequently applied in high-temperature reactors for efficient energy conversion. It operates through four main stages namely isentropic compression, isobaric heat addition (through external heat source), isentropic expansion in a turbine, and isobaric heat rejection.
Helium bubbles – These are nanoscale, high-pressure, inert gas-filled voids which form within the crystalline lattice of metals subjected to high-dose radiation (e.g., fusion or fission reactor components). Because of the near-zero solubility of helium in metals, helium atoms produced by (n, alpha) transmutation reactions, migrate and trap vacancies, precipitating into these bubbles.
Helix – It is a three-dimensional, smooth skew curve which winds around a cylinder or cone at a constant angle to the axis. It is a shape generated by a point rotating around a fixed axis while simultaneously moving along that axis at a constant rate relative to its rotation.
Helix angle – It is the angle between the helical path (such as a thread, gear tooth, or cutter flute) and the axial line (longitudinal axis) of a cylinder or cone. It defines the steepness of a helix, typically ranging from 5-degree to 45-degree, and is important for calculating load distribution, thrust, and efficiency in mechanical components like gears, screws, and cutting tools
Helmholtz coil – It is an arrangement of coils which is useful for producing a uniform magnetic field within a certain volume.
Helmholtz decomposition – It is a fundamental vector calculus theorem stating that any sufficiently smooth, fast-decaying vector field can be uniquely split into the sum of an irrotational (curl-free, longitudinal) part and a solenoidal (divergence-free, transverse) part.
Helmholtz energy (A) – It is a thermodynamic potential defined as ‘A = U – TS’, representing the maximum useful work (non-expansion work) obtainable from a closed, isothermal, and isochoric system. It signifies the internal energy (U) minus energy lost to thermal disorder (TS), where ‘T’ is absolute temperature and ‘S’ is entropy, making it an important measure for equilibrium in engineering systems.
Helmholtz free energy – It is a thermo-dynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature (isothermal). The change in the Helmholtz energy during a process is equal to the maximum quantity of work which the system can perform in a thermodynamic process in which temperature is held constant. At constant temperature, the Helmholtz free energy is minimized at equilibrium.
Helmholtz layer – It is a molecularly thin, compact layer of adsorbed ions at the surface of an electrode that balances the charge on the electrode’s surface. Acting as a parallel plate capacitor in electrical double layer theory, it forms the inner region of the electrified interface between an electronic conductor and an electrolyte, important for understanding colloidal stability and capacitor-like energy storage.
Helmholtz resonator – It is an acoustic device comprising a rigid-walled container of air (V) connected to the atmosphere by a narrow opening or neck (S, l), functioning as a mass-spring system which resonates at a specific low frequency. It absorbs or attenuates sound energy when incident waves match its natural frequency, normally used in engineering for exhaust mufflers and speaker ports.
Helmholtz theorem – It states that any sufficiently smooth, rapidly decaying vector field in three dimensions can be uniquely decomposed into the sum of an irrotational (curl-free) part and a solenoidal (divergence-free) part. It simplifies complex vector fields in electro-magnetism and fluid dynamics into manageable components namely a scalar potential (gradient) and a vector potential (curl).
Helmholtz’s law – It states that any sufficiently smooth, rapidly decaying vector field in 3D can be uniquely decomposed into the sum of an irrotational (curl-free) part and a solenoidal (divergence-free) part. It is foundational for Electro-magnetism, fluid dynamics, and acoustics.
Help-driven-type slitting lines – In the help-driven type slitting line, the torque applied to the slitter arbors, from the slitter driven motor, reduces the tension on the pulled strip to avoid snagging at the entry slitter knives. The helper torque is insufficient to drive the slitters alone, hence avoiding the speed-match issue in a purely driven-type slitting line. The help-driven-type slitting line is in the tight-line configuration.
Hematite ore – It is an oxide of iron, and one of that metal’s most common ore minerals. Hematite refers to a ferric oxide containing no crystal water, and its chemical formula is Fe2O3 (ferric oxide). The pure hematite theoretical iron content is 69.94 %. Its appearance is from red to light gray, sometimes black, and the stripes are dark red. It is normally known as ‘red mine’. The hematite crystal structure is different, from very dense to very loose and very soft powder, so the hardness is not the same. The former is generally between 5.5 and 6.5 on Mohs scale, while the latter is very low. The specific gravity is between 4.8 and 5.3. It melts at 1,565 deg C. it has metallic to splendent luster. Hematite is abundant in nature, but pure hematite is less, frequently co-existing with magnetite and limonite. Hematite ore is a direct-shipping ore with naturally high iron content.
Hemi-hydrate – It is specifically calcium sulphate hemi-hydrate (CaSO.1/2H2O), is an engineering material created by heating gypsum to drive off water, leaving one-half molecule of water per calcium sulphate molecule. Known as plaster of Paris, it is important for its hydration property, where it rapidly re-absorbs water to set into a hard, durable di-hydrate mass.
Hemi-sphere – It is a three-dimensional geometric shape which is half of a sphere. It is formed by cutting a sphere along its diameter. It has one curved surface and one flat circular base.
Hemispherical dome test – It is frequently referred to as the ‘limiting dome height’ (LDH) test or a type of cupping test (such as the Erichsen test), is a destructive sheet metal formability test used to determine a material’s capacity for stretching. It evaluates how much a sheet metal can be stretched under biaxial tension before failure, particularly useful for characterizing materials for deep drawing and stampings.
Hemispherical temperature – It refers to the temperature at which an ash sample forms a hemisphere when heated. This specific temperature is a key indicator of how an ash sample behaves when exposed to high temperatures and is determined by measuring the height of the ash cone, which is equal to be half of its base width.
Hemming – It is a bend of 180-degree made in two steps. First, a sharp-angle bend is made, next the bend is closed using a flat punch and a die. Hemming can be done in mechanical or hydraulic presses with separate pre-hem and finish-hem dies or a two-stage hem die. Also, hemming machines with hydraulic, pneumatic, or electric drives have been used. In order to ensure the best surface and hem radius quality, a process with a controlled pressure is necessary.
Hemming and seaming dies – These are specialized tooling used in stamping presses or press brakes to fold, bend, and join sheet metal edges, normally after a main forming operation like drawing or bending. These processes are critical for reinforcing edges, removing sharp burrs for safety, and joining two metal panels (such as automobile doors or food cans) without welding.
Hemming dies – These are specialized press brake tools used in sheet metal fabrication to fold the edge of a sheet onto itself, a process known as hemming. This technique is utilized to reinforce edges, remove sharp burrs, increase rigidity, and improve the structural integrity of components. The dies typically operate in a two-stage process (pre-bending to an acute angle, followed by flattening) to create a closed, rigid, and safe edge, often used in automotive body panels and home appliance casings.
Hemming machines – These are specialized equipment used to fold the edge of a metal sheet over onto itself (or over another sheet) to create a smooth, rounded, or reinforced edge. This process improves structural rigidity, hides sharp edges (burrs), and improves the overall aesthetic of the part.
Hemming operation – It is defined as a mechanical joining process where the outer edge of one sheet is folded over the outer edge of a second sheet, creating a mechanical interlock. It typically involves three steps namely flanging, pre-hemming, and the final hemming, and is normally used for joining dissimilar materials.
Henry’s law – It is a gas law which states that the quantity of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry’s law constant. In simple words, it can be said that the partial pressure of a gas in vapour phase is directly proportional to the mole fraction of a gas in solution.
HEPA filter – HEPA is an acronym for ‘high efficiency particulate air’. HEPA filter is a type of pleated mechanical air filter. This type of air filter can theoretically remove at least 99.97% of dust, pollen, mould, bacteria, and any airborne particles with a size of 0.3 micrometers. The diameter specification of 0.3 micrometers corresponds to the worst case i.e., the most penetrating particle size (MPPS). Particles which are larger or smaller are trapped with even higher efficiency. Using the worst-case particle size results in the worst-case efficiency rating (i.e. 99.97% or better for all particle sizes). All air filters need periodic cleaning and filter replacement to function properly.
Heptagon – It is a polygon with seven sides and seven angles. It is also sometimes referred to as a septagon. A heptagon can be regular, meaning all its sides and angles are equal, or irregular, meaning its sides and angles can vary.
Heptane – Its chemical formula is C7H16. It is a straight-chain (normal-chain) alkane and saturated hydro-carbon consisting of 7 carbon atoms and 16 hydrogen atoms. In engineering, particularly in the automotive and chemical sectors, n-heptane is a critical reference material defined as the zero point on the octane rating scale because of its tendency to cause engine knocking.
He pycnometry – It is a method for determining the skeletal density of powder samples by measuring their volume using helium gas in a controlled chamber system, where the density is calculated as the ratio of the mass to the sample volume. This technique is particularly useful for samples without closed or inaccessible pores, providing accurate density measurements under isothermal conditions.
HERF – It is an abbreviation for high-energy-rate forging. It is a closed-die hot-forging or cold-forging process in which the stored energy of high-pressure gas is used to accelerate a ram to unusually high velocities in order to effect deformation of the work-piece. Ideally, the final configuration of the forging is developed in one blow or, at most, a few blows. In high-energy-rate forging, the velocity of the ram, rather than its mass, generates the major forging force.
Herman Hollerith’s tabulating machines – These have been pioneering electro-mechanical data processing systems designed to automatically read, count, and sort information recorded as holes in paper cards. These machines revolutionized data handling by replacing slow, manual tabulation with a method which have been faster, more accurate, and considerably cheaper.
HERMES – It is a project management method which is and used by information technology (IT) and business organizations. It is a simplified project management method which can be adapted to projects with varying degrees of complexity. It provides document templates to expedite project-related work.
Hermetic compressor – It is a design for refrigeration and HVAC (heating, ventilation, and air conditioning) systems where the motor and compressor are combined on a single shaft, completely enclosed within a welded, pressure-tight steel casing. This sealed unit eliminates the need for shaft seals, preventing refrigerant leaks and providing low-maintenance, quiet, and durable operation, mainly in small-capacity applications.
Hermetically sealed – It is a construction in which there is zero ingress against entry of air or other gasses, moisture or dust.
Hermite cubic curve – It is a third-degree parametric polynomial spline used for smooth interpolation between data points, guaranteeing C1 or C2 continuity. It is defined by two endpoints and their respective tangent vectors, providing local control over the curve’s shape.
Hermite polynomials – These are a sequence of orthogonal polynomials Hn(x) defined on (minus infinity, infinity) with a Gaussian weight function, normally used for quantum mechanics, probability, and signal processing. They solve the quantum harmonic oscillator Schrödinger equation and provide solutions to the Hermite differential equation.
Hermitian Hamiltonian – It is a self-adjoint operator in quantum mechanics representing the total energy of a system, defined by its equality to its own conjugate transpose. This ensures real-valued energy eigenvalues and unitary time evolution, necessary for energy conservation and stable, reversible system dynamics.
Hermitian matrix – It is defined as a square complex matrix which equals its own conjugate transpose, meaning that the elements of the matrix are complex numbers and the elements are the conjugates of those in the original matrix.
Hermitian operator – It is a linear operator which equals its own adjoint, acting on a complex Hilbert space. Used extensively in quantum engineering, these operators represent physical observables (e.g., energy, momentum) since their eigenvalues are always real and their eigenvectors are orthogonal, ensuring valid, measurable results.
Hermitian transpose – It is also called conjugate transpose. It is an operation on a complex matrix which transposes the matrix (swaps rows and columns) and takes the complex conjugate of each element.
Heron’s fountain – It is a self-acting, non-perpetual hydraulic machine which uses gravity and pneumatic pressure to produce a water fountain. It is frequently used to demonstrate concepts of pneumatics, hydraulics, and fluid dynamics. It is an apparatus consisting of three vessels stacked vertically, a top open basin, a middle airtight water container, and a bottom airtight air supply container, connected by tubing. The fountain works by exploiting the difference in gravitational potential energy between the top and bottom containers. Water falling from the basin (top) to the bottom container pressurizes the air, which travels to the middle container, forcing water out of a nozzle.
Herringbone – It is a pattern made up of rows of parallel lines which in any two adjacent rows slope in opposite directions
Herringbone bearing – It is a plain, sleeve, or thrust bearing with herringbone-shaped oil grooves.
Herringbone gears – Teeth in these gears resemble the geometry of a herring spine, with ribs extending from opposite sides in rows of parallel, slanting lines. Herringbone gears have opposed teeth to eliminate side thrust loads the same as double helicals, but the opposed teeth are joined in the middle of the gear circumference. This arrangement makes herringbone gears more compact than double helicals. However, the gear centres are to be precisely aligned to avoid interference between the mating helixes.
Herringbone pattern – It is fractographic pattern of radial marks (shear ledges) that look like nested letters ‘V’. Herringbone pattern is typically found on brittle fracture surfaces in parts whose widths are considerably higher than their thicknesses. The points of the herringbones can be traced back to the fracture origin.
Herringbone wing – It consists of cleats on a conveyor belt arranged in a V-shape pattern for improved material grip, necessitating evaluations for wear, alignment, and overall condition to uphold effective material transport.
Herschel-Bulkley fluid – It is a type of non-Newtonian fluid which shows a yield stress and follows a flow behaviour characterized by a consistency index (K) and a flow behaviour index (n), allowing it to be modeled as a power law fluid’ at high shear rates.
Hersey number – It is a dimensionless parameter which characterizes the lubrication regime between two surfaces, mainly in the context of the Stribeck curve. It is defined as the product of dynamic viscosity and velocity divided by the load per unit length of the bearing. Essentially, it indicates how well a lubricant separates two surfaces under given conditions. The Hersey number is a ratio, meaning it does not have any units. It is a key component in a Stribeck curve, which plots the coefficient of friction against the Hersey number to show how friction changes with different lubrication conditions. The Hersey number (HN) can be calculated as HN = (n x N) / P where ‘n’ is the dynamic viscosity of the lubricant, ‘N’ is the entrainment speed (velocity), and ‘P’ is the load per unit length of the bearing. The Hersey number essentially represents the ratio of viscous forces to load-bearing forces. A higher Hersey number normally indicates a thicker lubricant film and potentially lower friction. The Stribeck curve, with the Hersey number on the x-axis, helps visualize the different lubrication regimes: boundary lubrication (low Hersey number, high friction), mixed lubrication, and hydrodynamic lubrication (high Hersey number, low friction). In simpler terms, the Hersey number helps us understand how much the lubricant is doing its job of separating surfaces and reducing friction under different operating conditions.
Hershey fonts – They are a collection of vector fonts developed in the late 1960s. They are originally designed for use with early cathode ray tube displays. They are defined by a series of coordinates, where each character is drawn using straight line segments, allowing for easy scaling and rotation. These fonts have been widely used in computer graphics, computer aided design (CAD) programmes, and more recently, in computer-aided manufacturing applications.
Hertz (Hz) – It is the unit of frequency in the International System of Units (SI), frequently described as being equivalent to one event (or cycle) per second. For high frequencies, the unit is normally expressed in multiples namely kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).
Hertz equation – It is also called Hertzian contact theory. It is an engineering, physics, and mechanics principle which calculates the contact area, deformation, and pressure distribution between two elastic, non-conforming bodies pressed together. It relates contact force, curvature, and material properties (Young’s modulus and Poisson’s ratio) to predict, for example, the maximum pressure between a sphere and flat surface.
Hertzian contact area – It is the contact area (also, diameter or radius of contact) between two bodies calculated as per the Hertz’s equations of elastic deformation. It is also the apparent area of contact between two non-conforming solid bodies pressed against each other, as calculated from Hertz’s equations of elastic deformation.
Hertzian contact pressure – It is the pressure at a contact between two solid bodies calculated as per the Hertz’s equations of elastic deformation. It is also the magnitude of the pressure at any specified location in a Hertzian contact area, as calculated from Hertz’s equations of elastic deformation. Hertzian pressure -It is also called hertzian contact stress. It refers to the localized, compressive stress which develops when two curved, elastic, and normally non-conforming surfaces (such as a ball on a race or a cylinder on a flat surface) are pressed together. This theory is used to calculate the resulting elliptical or rectangular contact area, the pressure distribution, and the sub-surface shear stresses which lead to fatigue, cracking, or yielding in materials like gears and bearings.
Hertzian stress – It is the pressure at a contact between two solid bodies calculated according to Hertz’s equations for elastic deformation. The theoretical area of contact between two non-conforming surfaces is frequently quite small. The interaction between these surfaces is frequently described as either point or line contact. Common examples of point contact are mating helical gears, cams and crowned followers, ball bearings and their races, and train wheels and rails. If the mating parts can be considered semi-infinite and if material behaviour is linearly elastic, then the local stress state can be described by Hertzian theory, as long as the contacting surfaces can be modeled as quadratic functions of those spatial coordinates defining the surfaces. Even in the absence of friction, the resulting three-dimensional stress state is quite complex, and although the local stress state is compressive, i.e., the principal stresses beneath the load are negative, large subsurface shear stresses, which can serve as crack initiation sites, exist beneath the load.
Hertz interference (50/60 hertz) – It refers to electrical noise, mainly caused by alternating current power transmission lines, generators, or equipment, which disrupts sensitive electronic, seismic, or bioelectrical signals. It appears as unwanted, single-frequency harmonic noise at 50 hertz or 60 hertz, frequently resulting in spikelike, narrowband interference.
Hertz’s compression – It is frequently termed hertzian contact theory). It refers to the mathematical modeling of the deformation, contact area, and stress distribution between two curved, elastic, and frictionless bodies when pressed together. It is necessary for understanding how surfaces deform under localized, high-pressure, but technically ‘non-conforming’ loading, such as in bearing balls or gear teeth.
Hertz (Hz) sine wave – It is a continuous, smooth, periodic oscillation, shaped like a sine function graph (y = A sin (2pi x f x t + phi), representing a signal which completes a specific number of full cycles per second. One hertz equals one cycle per second, defining the frequency (f) of the wave.
Hertz supply – It refers to the frequency of alternating current (AC) electricity, measuring how many cycles the current completes per second. It represents the rate at which electricity changes direction. Standard power supply frequencies are 50 Hertz (50 cycles per second) and 60 Hertz (60 cycles per second).
Hertz theory – It refers to the theoretical framework which describes the normal contact between elastic spheres, focusing on the contact area, pressure distribution, and deformation under frictionless conditions. It provides equations for calculating contact pressure, contact force, and displacements at the contact surfaces based on material properties and geometrical parameters.
Hessenberg form – It is a sparse matrix representation, normally used in numerical engineering to simplify eigenvalue calculations, where all elements below the first sub-diagonal (or above the first super-diagonal) are zero. It acts as an ‘almost’ triangular matrix, frequently achieved through Householder transformations to speed up algorithms like the QR algorithm while preserving original matrix eigenvalues.
Hessenberg matrix – It is a square matrix which is ‘almost’ triangular, used for efficient numerical computations like eigenvalue algorithms. An upper Hessenberg matrix has zero entries below the first sub-diagonal, while a lower Hessenberg matrix has zeros above the first super-diagonal.
Hessian matrix – It is a square matrix of second-order partial derivatives of a scalar-valued function, describing the local curvature of a multivariable function. It represents the rate of change of the gradient and is used extensively for optimization to identify local minima, maxima, and saddle points, particularly in Newton-based numerical methods
Hess’ law of constant heat summation – Hess’ law states that the total enthalpy change during the course of a chemical reaction is the same whether the reaction is completed in one step or in multiple steps.
Hetero-atom content – It refers to the presence of non-carbon atoms, such as nitrogen and sulphur, in crude oil, which considerably influences its processing methods and the tendency to foul catalysts and form sludge.
Hetero-coagulation – It is typically irreversible aggregation of dissimilar colloidal particles (different sizes, surface charges, or compositions) in a suspension. It is driven by opposite electrical charges (electrostatic interaction) or, in some cases, shear, resulting in unique structured materials, such as, raspberry-like particles or ceramic-coated materials. It is widely used in nano-technology to create nano-composites, improve filler-polymer adhesion, and control coating structures.
Hetero-deformation induced strengthening – It is a strengthening mechanism in heterostructured materials which simultaneously increases strength and ductility, bypassing the traditional strength-ductility trade-off. It arises from the strain incompatibility between soft and hard domains during plastic deformation, which triggers geometrically necessary dislocations (GNDs) and generates long-range back stresses (hetero-deformation induced stress) in soft zones, improving strain hardening and delaying yielding.
Hetero-deformation induced stress – It is an additional internal stress generated in hetero-structured materials because of the strain incompatibility between hard and soft domain zones during plastic deformation. It arises from geometrically necessary dislocations (GNDs) piling up at interfaces, creating back stress in soft zones and forward stress in hard zones, considerably increasing strength and ductility.
Heterodyne receiver – It is an architecture which improves radio signal processing by mixing an incoming high-frequency RF (radio frequency) signal with a local oscillator to produce a lower, fixed intermediate frequency. This allows high-gain amplification and high-selectivity filtering at a constant intermediate frequency, resulting in superior sensitivity and noise rejection compared to direct conversion.
Heterogeneity – This term is used in statistics to describe samples or individuals from different populations, which differ with respect to the phenomenon of interest. If the populations are not identical then they are said to be heterogeneous, and by extension, the sample data is also said to be heterogeneous.
Heterogeneity effect – It refers to the impact which variations in material properties, structure, or system components, such as porosity, permeability, or composition, have on overall performance and behaviour. It shows that a system is not uniform, leading to non-linear, unpredictable, or uneven responses compared to a homogeneous system.
Heterogeneous – It is the descriptive term for a material consisting of dissimilar constituents separately identifiable. It is a medium consisting of regions of unlike properties separated by internal boundaries. It is to be noted that not all the non-homogeneous materials are necessarily heterogeneous.
Heterogeneous alloy – It is a metallic material comprising two or more distinct phases (e.g., ferrite and cementite) with non-uniform atomic distribution, differing in composition or structure, and frequently visually distinguishable. Engineered for improved strength / ductility through ‘strain delocalization’, these materials frequently show selective corrosion.
Heterogeneous catalysts – These are catalysts which exist in a different phase from the reactants, showing advantages such as reusability, ease of separation from products, and lower environmental impacts in processes like bio-diesel production. They can be categorized into alkali-based and acid-based types, with each type having distinct properties and applications in catalyzing reactions.
Heterogeneous combustion – It refers to an exothermic chemical reaction process where the fuel and oxidant exist in different physical phases (e.g., solid-gas or liquid-gas), frequently occurring at an interface. It is characterized by diffusion-controlled mechanisms, such as surface oxidation of solid fuel (char) or combustion of liquid spray droplets, needing transport of species across phase boundaries.
Heterogeneous contact – It refers to the interface formed between materials with distinct properties (e.g., stiffness, frictional characteristics, composition) or the interaction of a surface with non-uniform, randomly distributed inhomogeneities (such as defects, voids, or inclusions). This field focuses on analyzing, modeling, and optimizing the physical behaviour (friction, stress, displacement) at these non-uniform interfaces.
Heterogeneous equilibrium – In a chemical system, a state of dynamic balance among two or more homogeneous phases capable of stable coexistence in mutual or sequential contact.
Heterogeneous group – It is a diverse assembly of individuals, systems, or components with varying backgrounds, skills, or, in technical contexts, different processing units working together towards a common functional goal. These groups leverage varied perspectives or technical capabilities to improve problem-solving, performance, and adaptability in complex systems, such as mixed-material structures.
Heterogeneous ion-exchange membranes – These are composite materials produced by dispersing fine ion-exchange resin particles (60 % to 70 %) within an inert, thermoplastic binder polymer (e.g., poly-vinyl chloride, polyethylene). They are characterized by a macroscopically non-uniform structure, offering a low-cost, mechanically durable alternative to homogeneous membranes.
Heterogeneous material – It is a substance composed of two or more distinct phases, components, or constituents with non-uniform physical, mechanical, or chemical properties throughout its structure. Unlike homogeneous materials, heterogeneous materials show substantial, localized variations in composition, structure, or strength at the microscopic or macroscopic levels.
Heterogeneous membranes – These are non-uniform, ion-selective, or specialized separation materials constructed by dispersing functional filler particles (e.g., resin) within an inert binder polymer matrix. Designed for high mechanical strength and cost-effective, large-scale production, they typically feature lower conductivity and higher electrical resistance compared to homogeneous membranes, making them suitable for industrial applications.
Heterogeneous network – It is a, multi-tier communication infrastructure which integrates diverse access technologies, operating systems, or device types (e.g., macro-cells, small cells, Wi-Fi) to improve capacity, coverage, and flexibility. These networks intelligently manage different signal power levels and protocols to handle traffic efficiently.
Heterogeneous nucleation – It is the process where a new phase (solid, liquid, or bubble) forms preferentially on pre-existing surfaces, such as inclusions, container walls, or intentionally added nucleating agents, rather than spontaneously in a pure bulk phase. This mechanism lowers the activation energy barrier, allowing phase changes to occur at much smaller undercooling levels.
Heterogeneous reaction – It is a chemical process involving reactants in two or more different phases (solid, liquid, or gas). These reactions occur at the interface or boundary between phases, frequently necessitating mass transfer steps (diffusion, adsorption) alongside chemical reaction kinetics.
Heterogeneous regime – It refers to a system or flow characterized by non-uniform, distinct phases (e.g., solid-liquid or gas-liquid) with boundaries, frequently resulting from high-energy inputs like fast fluid velocities. Unlike homogeneous systems, these regimes involve complex, chaotic interactions, such as large bubble coalescence in bubble columns or particle settling in slurry transport.
Heterogeneous sensor systems – These comprise networks or integrated units using diverse sensor types, technologies, and modalities to collect, transmit, and process varied, multi-source data. Engineered for, and to overcome, limitations of identical sensors, these systems handle differences in sampling rates, data types, communication protocols, energy levels, and processing capabilities, needing sophisticated data fusion to achieve superior, comprehensive monitoring.
Heterogeneous structure – It refers to metallic materials possessing non-uniform micro-structures, consisting of distinct zones or phases which differ in grain size, crystal structure, orientation, or chemical composition. These regions interact during deformation to generate hetero-deformation induced (HDI) stress, improving both strength and ductility. It also refers to a material or system composed of non-identical components, domains, or phases which possess different physical, mechanical, or chemical properties.
Heterogeneous system – It is a computing environment integrating diverse, non-identical processing components within a single platform. Designed to improve performance, energy efficiency, and specialized workload processing, these systems combine different architectures to manage varied, complex tasks more efficiently than homogeneous systems.
Heterogeneous wireless access network – It is a framework integrating multiple radio access technologies (RATs), such as cellular, Wi-Fi, and satellite, to optimize connectivity. It enables mobile terminals to, seamlessly, switch between networks to achieve the best quality of service (QoS) and manage capacity.
Heterogenite – It is a naturally occurring, rare cobalt oxyhydroxide mineral, CoO(OH) or HCoO2, which serves as a substantial secondary source of cobalt.
Heterojunction – It is the interface between two dissimilar semiconductor materials with different bandgaps (e.g., n-AlGaAs / p-GaAs), engineered to manipulate charge carrier behaviour. Unlike homojunctions, they utilize band offsets at the junction to control electron / hole transport, enabling high-performance, high-speed, and high-efficiency solid-state devices like transistors, lasers, and solar cells.
Heterojunction bipolar transistor – It is a type of bipolar junction transistor which uses different semi-conductor materials for the emitter and base regions, creating a heterojunction. The heterojunction bipolar transistor improves on the bipolar junction transistor in that it can handle signals of very high frequencies, up to several hundred giga hertz.
Heterojunction formation – It is the coupling of semiconductors which facilitates charge transfer and spatial charge separation, where electron flow occurs from a semiconductor with a higher Fermi level to one with a lower Fermi level, hence improving photocatalytic performance and reducing electron / hole recombination.
Heterojunction with intrinsic thin film layer – It is a type of solar cell which is composed of a mono-thin-crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers. These solar cell modules are more efficient than typical crystalline modules, but they are more expensive.
Heteroleptic metal carbonyls – These are frequently referred to simply as mixed-ligand carbonyls. These are a type of coordination complex where a transition metal is bonded to carbon mono-oxide (CO) ligands one or more other types of ligands. They differ from homoleptic metal carbonyls, which contain only carbon mono-oxide ligands attached to the metal center, e.g., Ni(CO)4, and Fe(CO)5.
Hetero-modulus ceramics – These are also called hetero-modulus ceramic-ceramic composites. These are thermal shock-resistant materials, which can be applied, because of their less common microstructures and physicochemical properties, in aerospace and nuclear engineering and in different media, including the extreme environments, at high and ultrahigh temperatures. The main feature of this type of composite materials is the combination of hard ceramics having high Young’s modulus with the low-modulus phases of graphite and graphite-like boron nitride.
Hetero-modulus materials – These are a specific class of composite materials designed to improve toughness and machinability by combining a rigid ceramic matrix (high Young’s modulus) with inclusions or layers of a considerably softer, low-modulus material. These are multi-phase composites which intentionally incorporate materials with ‘considerably different’ elastic moduli, specifically, combining a high-modulus (stiff) matrix with low-modulus inclusions (e.g., graphite or hexagonal boron nitride). The main objective is to alleviate the inherent brittleness and poor machinability of high-strength ceramics.
Heteronuclear dipolar interaction – It is the direct, through-space magnetic coupling between two different nuclear spins (e.g., 1H and 13C) in solid-state NMR (nuclear magnetic resonance), causing spectral broadening. It refers to the coupling between spins of different nuclei, such as protons and carbon, which can lead to broadening in spectra and is influenced by the dipolar coupling strength. These interactions can be manipulated using radiofrequency fields to average the effects and improve spectral resolution.
Heteroscedasticity – In regression analysis, the property that the conditional distributions of the response variable ‘Y’ for fixed values of the independent variables do not all have constant variance. Non-constant variance in a regression model results in inflated estimates of model mean square error. Standard remedies include transformations of the response, and / or employing a generalized linear model.
Hetero-structure – It is a semiconductor device which is built of two or more dissimilar materials.
Heuristic argument – It is a non-rigorous, experience-based, or intuitive method used to quickly reach a satisfactory solution for complex, ill-defined, or uncertain problems, frequently involving simplifications or rules of thumb rather than exhaustive calculations. It serves as a practical, rapid, and speculative technique for decision-making.
Heuristic reasoning – It is a practical, experience-based problem-solving approach using ‘rules of thumb’, intuition, and simplified strategies to find satisfactory solutions efficiently. It enables engineers to quickly navigate complex, non-deterministic problems where exhaustive analysis or perfect optimization is impractical.
Heuristics – These are experience-based, practical ‘rules of thumb’ or ‘shortcuts’ used to solve complex problems, estimate design parameters, or make rapid, satisfactory decisions when exhaustive calculations are impossible or unnecessary. They do not guarantee optimal or 100 % correct solutions but provide reasonable, ‘good enough’ approximations quickly.
Heuristic techniques – These are methods of problem-solving approach which uses practical, efficient, and sometimes imperfect strategies to find solutions, especially when a perfect solution is difficult or impossible to achieve. These are essentially a ‘rule of thumb’ or mental shortcut which helps in making decisions or finding answers quickly. Heuristic methods do not always lead to the best possible solution, but they provide a good enough solution in a reasonable quantity of time. They rely on past experiences, patterns, and experimentation to guide the search for solutions.
Hexa – It is the short form of hexa-methylene-tetramine, a source of reactive methylene for curing novolacs.
Hexa-chloro-ethane – Its chemical formula is C2Cl6. It is a volatile chlorinated hydro-carbon, appearing as a crystalline solid. It is a halogenated hydro-carbon consisting of six chlorines attached to an ethane. It is a white to pale yellow solid which is unstable in air and evaporates gradually. It smells like camphor when its concentration in air and water are 150 ppb (parts per billion) and 10 ppb, respectively. Hexa-chloro-ethane (HCE) itself does not catch fire easily. However, in aqueous non-biological conditions, it has been determined that hexa-chloro-ethane is unstable and non-enzymatic de-chlorination in the absence of nicotinamide adenine dinucleotide phosphate (NADP) occurs. It rapidly degrades in soil or groundwater. It is mainly used as a high-temperature degasifier for removing hydrogen bubbles from molten aluminum and magnesium alloys.
Hexa-chloro-ethane smoke – It is a, dense white, pyrotechnically generated, inorganic obscurant aerosol. It is engineered as a ‘burning-type’ smoke produced by the exothermic, self-perpetuating reaction of hexa-chloro-ethane (HCE), zinc oxide (ZnO), and a metal fuel (typically aluminum).
Hexa-fluoro-silicic acid (H2SiF6) – It is a strong, colourless, and highly corrosive inorganic aqueous acid, normally produced as a byproduct in phosphoric acid manufacturing. Industrially used for water fluoridation, metal plating, and chemical synthesis, it is a key reagent in producing aluminum fluoride, silicon, and synthetic cryolite. It exists only in aqueous solutions, frequently represented as (H3O)2SiF6.(H2O)n.
Hexagon – It is a two-dimensional shape which has six sides and six angles. It is a polygon, meaning it is a closed shape made up of straight lines. A regular hexagon has all six sides of equal length and all six interior angles equal to 120 degrees.
Hexagonal bolt – It is also known as a hex bolt. It is a type of threaded fastener characterized by its six-sided (hexagonal) head. It’s designed to be tightened or loosened with a wrench or socket, which engages with the six flat sides of the head. Hexagonal bolts are normally used to secure two or more components together by threading the bolt shaft into a compatible threaded hole or nut.
Hexagonal close-packing – It is a structure containing two atoms per unit cell located (0, 0, 0) and (1/3, 2/3, 1/2) or (2/3. 1/3, 1/2). It is one of the two ways in which spherical objects can be most closely packed together so that the closed-packed planes are alternately staggered in the order A-B-A-B-A-B. Each atom has twelve nearest neighbours in hexagonal close packing. In the ideal structure, the distance between the planes is 1.633a, where a is the distance between the atoms. Some metals with hexagonal close-packed crystal structures include cobalt, cadmium, zinc, and the alpha phase of titanium.
Hexagonal close-packed – It is a highly efficient crystal structure (74 % packing density) used by metals like titanium and magnesium, defined by an A-B-A-B-A-B stacking sequence of atomic layers. It features a hexagonal unit cell with 6 atoms, where each atom has a coordination number of 12.
Hexagonal close-packed alpha phase – It refers to the stable, low-temperature, hexagonal close-packed (hcp) crystal structure found in metals like titanium, magnesium, and zinc. It features an A-B-A-B-A-B stacking sequence with a high atomic packing factor (74 %) and limited slip systems, typically resulting in high strength and anisotropy.
Hexagonal close-packed materials – These are metals with a crystal structure defined by a high-density 74 % packing efficiency, with atoms arranged in an A-B-A-B-A-B stacking sequence (alternating hexagonal planes). Characterized by 12-fold coordination and a c/a ratio ideal at 1.633, these structures are common in metals like magnesium, titanium, zinc, and beryllium.
Hexagonal close-packed metals – These are metals with a crystal structure defined by an atomic packing sequence of A-B-A-B-A-B, creating a densely packed (74 % efficiency) hexagonal prism unit cell. Common metals are titanium, magnesium, zinc, and beryllium. These structures feature a 12-coordination number, high plastic anisotropy, and distinct deformation mechanisms, frequently needing specialized processing for applications needing high strength-to-weight ratios.
Hexagonal close-packed structures – These are crystalline arrangements with a high-density, A-B-A-B-A-B stacking sequence (74 % packing efficiency) featuring 12-fold coordination. Common in metals like titanium, magnesium, and zinc, they form hexagonal prism unit cells, frequently showing lower ductility and higher strength because of the limited slip systems, frequently relying on deformation twinning.
Hexagonal crystal family – In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While normally confused, the trigonal crystal system and the rhombohedral lattice system are not equivalent. In particular, there are crystals which have trigonal symmetry but belong to the hexagonal lattice (such as alpha-quartz). The hexagonal crystal family consists of the 12-point groups such that at least one of their space groups has the hexagonal lattice as underlying lattice, and is the union of the hexagonal crystal system and the trigonal crystal system. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral.
Hexagonal crystal structure – It is a type of crystal structure characterized by having three equal-length axes (a, b, and c) at 120-degree angles to each other in a plane, with a fourth axis (c) perpendicular to that plane and of a different length. This arrangement results in a unit cell that can be visualized as a prism with a hexagonal base.
Hexagonal duct – It is an enclosed conduit with a six-sided (hexagonal) cross-section, normally used in thermal management, nuclear reactors, and fluid transportation, such as in compact heat exchangers. It acts as a passage to transport fluid, frequently with longitudinal fins for improved heat transfer.
Hexagonal lattices for crystals – These consist of having two equal coplanar axes, ‘a1’ and ‘a2’, at 120-degree to each other and a third axis, ‘c’, at right angles to the other two. ‘c’ may or may not equal ‘a1’ and ‘a2’.
Hexagonal metals – These metals are materials characterized by a ‘hexagonal close-packed (HCP) crystal structure, defined by an atomic arrangement featuring limited slip systems and the activation of deformation twinning. These materials, including titanium (Ti), magnesium (Mg), and zirconium (Zr), are known for their high strength-to-weight ratio, anisotropy, and corrosion resistance, normally applied in nuclear engineering.
Hexagonal nut – It is a type of nut with a hexagonal (six-sided) shape, designed to be used with a bolt or screw to fasten two or more parts together. The hexagonal shape allows for a good grip with a wrench, enabling the user to apply torque and create a secure bolted joint. Hex nuts are widely used in various applications, from simple household repairs to complex machinery and construction.
Hexagonal plate – It is a planar structural element characterized by a six-sided (hexagonal) boundary. It is defined as a thin, flat structural component, frequently used in civil, mechanical, and materials engineering for its superior load-carrying capacity, efficient space-filling (tessellation), and high-strength-to-weight ratio, particularly when subjected to bending or compression.
Hexagonal prism – It is a 3D polyhedron with two parallel, congruent hexagonal bases connected by six rectangular lateral faces. It features 8 faces, 18 edges, and 12 vertices. This structure is used for its strength and ability to pack tightly, such as in structural blocks, nut heads, and ‘graphite fuel elements’ (GFE) in nuclear reactors.
Hexahedron – It is a 3D polyhedron with six faces, normally used as an 8-node, 6-faced brick element in finite element analysis (FEA) to discretize volumes for stress, thermal, or fluid simulations. These elements, frequently called ‘hex’ elements, improve simulation accuracy and efficiency compared to tetrahedra because of their superior capability to represent structural deformation, especially when aligned with geometry, and their reduced susceptibility to numerical ‘locking’.
Hexahedron element – It is a 3D, 8-node solid finite element (frequently called a ‘brick’ element) with six quadrilateral faces, used for modeling continuum mechanics and structural analysis. These elements possess three degrees of freedom per node (translations in x, y, z) and are highly effective for capturing stress gradients, normally outperforming 4-node tetrahedral elements.
Hexanediol – It refers to an aliphatic alcohol which is utilized to modify phase separation and hydrogel formation, particularly through its ability to disrupt hydrophobic interactions and influence the permeability barrier of the nuclear pore complex.
Hexavalent chromium (Cr6) – It is a highly toxic, carcinogenic form of chromium in the ‘+6’ oxidation state, widely used for electroplating, stainless steel production, pigments, and corrosion inhibitors. It acts as a strong oxidizer, frequently generated in industrial settings through high-temperature oxidation of ‘Cr3’ (tri-valent chromium), such as during welding or through surface treatment processes.
Hexcel composites – These are high-performance materials consisting of fibre-reinforced plastics (FRPs), prepregs, and honeycomb technologies, designed for superior strength-to-weight ratios and structural integrity. They utilize carbon, glass, or aramid fibres, and thermoset / thermoplastic resins, e.g., epoxy, bismaleimide (BMI). These materials are extensively used in industrial applications to reduce weight and improve performance.
Hex head fastener – It is a type of threaded fastener, typically a bolt or screw, characterized by a head shaped like a hexagon. This hexagonal head allows for easy gripping and tightening with a wrench or socket, making it a common choice for various applications.
Hexogen – It is also known as RDX (Royal Demolition Explosive) or cyclonite. It is a powerful and widely used explosive. It is a white, crystalline solid with the chemical formula C3H6N6O6, and is classified as a nitramine explosive. RDX is known for its high energy density, rapid reaction speed, and relatively low sensitivity to external stimuli. It is a key component in mining applications and is also used in controlled demolitions.
HEX tails – It is the types of uranic material arising from the uranium enrichment process (part of the nuclear fuel production cycle).
H-factor – It is a dimensionless, single-variable metric which combines temperature and time to calculate the extent of lignin removal (delignification) during the kraft pulping process. It represents the integral of the relative reaction rate, allowing operators to monitor cooking efficiency.
HHV – It is the abbreviation for higher heat value and is the quantity of heat released by a unit mass or volume of fuel when combusted, with the products returning to a temperature of 25 deg C, including the latent heat of vapourization of water. It is also referred to as gross calorific value (GCV).
Hidden costs – These costs are also known as invisible costs. These are the costs which are not visible to the management. These costs are expenses which are not apparent or accounted for in a budget. They frequently arise from inefficiencies, oversight, or unexpected events, making them harder to spot.
Hidden layer neuron – It is a fundamental computational unit within an ‘artificial neural network’ (ANN) located between the input and output layers. It acts as an intermediate processing node which applies weighted sums, adds bias, and passes the result through an activation function to transform input data into abstract, higher-level representations.
Hidden layer nodes – These are the fundamental processing units within the hidden layers of an artificial neural network, positioned between the input and output layers. They are responsible for intermediate data transformation, feature extraction, and learning complex, non-linear patterns from input data. The number of hidden nodes is an important hyper-parameter: too few limit learning capacity (underfitting), while too many lead to excessive computation and memorization (overfitting).
Hidden message – It refers to a message which is concealed within another item, known as a spread work, using techniques which prevent detection by adversaries. This method allows for secret correspondence by embedding information in innocuous media such as images, sound, video, or text.
Hidden neurons – These are the fundamental processing units located within the hidden layers of an artificial neural network, situated between the input and output layers. They are termed ‘hidden’ since their inputs and outputs are not directly observable in the final output of the network, acting as an intermediary layer which transforms input data into a higher-level representation.
Hidden node problem – It is a wireless networking issue where a node (C) is outside the signal range of another node (A, yet both communicate with a common central node (B). Since ‘C’ cannot detect A’s transmission, it wrongly senses an idle channel and transmits simultaneously, causing collisions at ‘B’. This results in substantial packet loss and reduced network efficiency, normally mitigated by ‘request-to-send’ / ‘Clear-to-send’ (RTS / CTS) mechanisms.
Hidden nodes – In wireless communications (networking) hidden nodes refer to a situation where a node is unable to detect communications between other nodes, leading to potential message collisions when multiple nodes attempt to send signals to the same destination simultaneously. This issue normally affects the performance of larger ad hoc and wireless mesh networks. In ‘artificial Neural networks’ (ANNs), hidden nodes are the processing units located within the layers between the input layer and the output layer. In complex networks (e.g., neural circuits, social networks), a hidden node is a vertex whose dynamics cannot be measured or observed directly.
Hiding power – It is the ability of a paint to mask the colour or pattern of a surface. It is normally expressed as square metre per litre.
Hierarchical Bayesian approach – It is a statistical method which models complex data across multiple, nested levels, such as component, sub-system, and system levels, sing Bayes’ theorem to account for uncertainty and share information (‘borrow strength’) between related groups. It enables robust, data-informed decision-making in sparse-data scenarios by treating parameters as probability distributions rather than fixed values.
Hierarchical Bayesian models – These are probabilistic, multi-level frameworks which model complex data by nesting parameters, allowing ‘borrowing strength’ across groups to improve estimation precision, particularly with sparse data. They define parameters as distributions rather than fixed values, using hyper-parameters at higher levels to govern lower-level parameters.
Hierarchical block – It is a modular design approach which groups multiple components, circuits, or functions into a single, higher-level block representation. It organizes complex schematics or simulations, allows for reuse, and simplifies design, enabling, for example, a processor’s schematic to be represented by a single symbol in a main block diagram.
Hierarchical clustering – It is an unsupervised machine learning method which builds a nested, tree-like structure of clusters (dendrogram) by iteratively merging (agglomerative) or splitting (divisive) data points based on similarity metrics. It enables hierarchical categorization, frequently used in exploratory data analysis to determine the optimal number of clusters without pre-selection.
Hierarchical control system – It is a structured configuration of controllers, devices, and software organized in a multi-layered, tree-like architecture to manage complex systems. It breaks down tasks by delegating decision-making to different levels, with high-level optimization at the top and low-level, real-time control at the bottom.
Hierarchical management system – It is a structured organizational design which ranks individuals or entities by levels of authority, featuring a top-down chain of command from senior leadership to staff. It operates like a pyramid, with clear, defined roles and reporting lines which facilitate structured decision-making, accountability, and communication.
Hierarchical mode – It is a structured, multi-level approach used to manage complexity by decomposing systems into smaller sub-systems (infimals) coordinated by higher-level (supremal) controllers. It organizes data or processes in a tree structure, where each node typically has one parent, to improve scalability, manage traffic, or optimize performance, such as in image coding or network control.
Hierarchical network – It is a design model which organizes complex network infrastructure into three distinct, manageable, and functional tiers: namely core, distribution, and access. This structured approach boosts network scalability, performance, and reliability while easing troubleshooting and maintenance.
Hierarchical port – It connects different levels of a schematic or system model, allowing signals to pass vertically between nested blocks and their parent, or laterally within a folder. It uses specialized port symbols acting as pins, important for organizing complex designs, enabling top-down design, and supporting modularity.
Hierarchical system – It is a structure where elements (people, groups, or things) are arranged in ordered levels of rank, importance, or authority, forming a pyramid-like chain of command, with higher levels controlling lower ones, seen in organizations. Communication flows up and down, with clearer responsibility but potential delays, and promotion offers advancement.
Hierarchical task analysis – It is a systematic human-factors method which decomposes complex tasks into a hierarchy of goals, sub-goals, operations, and plans. It maps user behaviour to understand, optimize, and train for complex workflows by breaking down high-level objectives into actionable, structured sub-steps.
Hierarchization – It is the systematic, top-down structuring of components, processes, or decisions into ranked levels based on importance, functionality, or abstraction. It organizes complex systems by defining relationships (e.g., control, priority) to manage complexity, improve efficiency, and ensure adherence to objectives.
Hierarchy of controls – It is a structured, five-tier framework used to prioritize hazard mitigation, ranging from the most effective (removing the risk) to the least effective (protecting the worker from the risk). In the context of metallurgical operations, such as smelting, welding, casting, and metal finishing, this system is used to combat risks like toxic fumes, extreme heat, heavy machinery hazards, and noise. The five levels of control, in order of decreasing effectiveness, are (i) elimination, (ii) substitution, (iii) engineering controls, (iv) administrative controls, and (v) personal protective equipment (PPE).
High accuracy – It refers to the minimal difference between a measured value and the true, absolute, or standard value, indicating very low systematic error or bias. It indicates a high degree of conformity to a target, ensuring reliability and minimal deviation in critical applications, frequently achieved through rigorous calibration and advanced, stable, and precise equipment.
High-alloy austenitic steels – These are corrosion-resistant iron-based alloys characterized by a stable face-centered cubic (fcc) crystal structure, achieved with high nickel (higher than 8%), chromium (higher than 16 %), and frequently molybdenum or nitrogen additions. These non-magnetic materials possess very good toughness, ductility, and high-temperature strength, with improved resistance to chlorides and acids compared to standard 300-series stainless steel grades.
High alloy cast steels – These steels are extensively used for their corrosion resistance in aqueous media at or near room temperature and for service in hot gases and liquids at elevated temperatures (more than 650 deg C). High alloy cast steels are very frequently specified on the basis of composition. Some of the high alloy cast steels show several of the properties of cast carbon and low alloy steels. Some of the mechanical properties of these grades (e.g. hardness and tensile strength) can be altered by suitable heat treatment. The high alloy cast steel grades which contain more than 20 % to 30 % chromium + nickel, however, do not show the phase changes observed in plain carbon and low alloy steels during heating or cooling between room temperature and the melting point. These materials are hence non hardenable, and their properties depend on composition rather than heat treatment. Hence special consideration is to be given to each grade of high alloy cast steel with regard to casting design, foundry practice, and subsequent thermal processing (if any).
High-alloy graphitic cast iron – It is used mainly for applications needing corrosion resistance or a combination of strength and oxidation resistance. This type of cast iron is produced in both flake graphite (gray cast iron), or spheroidal graphite (ductile cast iron).
High-alloy iron rolls – These are specialized metallurgical components used in rolling mills, defined as cast irons containing a total alloying element content higher than around 4 % to 5 % (such as chromium, nickel, molybdenum, and vanadium) to provide superior wear resistance, hardness, and thermal fatigue resistance compared to conventional cast iron. They are designed for severe service conditions in both hot and cold rolling, often featuring complex microstructures, such as high-chromium white iron, with hard eutectic carbides embedded in a matrix.
High alloy steel – These steels include steels with a high degree of fracture toughness. High alloy steels are ultra-high strength steels and consist of corrosion resistant steels, heat resistant steels, and wear resistant steels. High alloy steels also include maraging steels, austenitic manganese steels, tool steels, and stainless steels.
High-alloy tool steels – These are specialized, high-carbon steels containing over 5% (frequently 6 % to 30 %) total alloying elements, designed for extreme wear resistance, hardness, and heat resistance up to 600 deg C. They are important crucial for cutting, forming, and molding tools, using refractory metals (chromium, molybdenum, vanadium, and tungsten) to form hard carbides.
High alumina refractory – It is a refractory composed predominantly of alumina and / or alumino-silicate containing higher than or equal to 45 % by mass of aluminium oxide. ISO 10081-1 contains compositional data on high alumina refractories.
High aluminum defect – It is an alpha-stabilized region in titanium containing an abnormally large quantity of aluminum which can span a large number of beta-grains. It contains an inordinate fraction of primary alpha, but has a micro-hardness only slightly higher than the adjacent matrix.
High-angle boundary migration – It is the movement of boundaries with misorientation angles typically higher than 15-degree, driven by energy reduction during processes like recrystallization or grain growth. It involves the transfer of atoms across the boundary interface, frequently mediated by atomic-level jumps or the motion of defects.
High-angle boundaries – These are grain boundaries with a misorientation angle higher than around 15-degree between adjacent crystallites, separating grains with considerably different crystal orientations. Unlike low-angle boundaries (less than 10-degree to 15-degree), high-angle boundaries have high atomic disorder, higher energy, and act as significant barriers to dislocation motion, important for determining material strength, ductility, and diffusion.
High-angle grain boundaries – These consist of a type of grain boundary in poly-crystalline materials where the misorientation angle between the adjoining crystal lattices is higher than 15-degree. These boundaries have high interfacial energy (0.5 joules per square meter to 1 joule per square meter) atomic disorder, and act as important barriers to ) motion, frequently increasing material strength while enabling high diffusivity and chemical reactivity. These boundaries are characterized by a higher energy state and a more disordered structure compared to low-angle grain boundaries (LAGBs).
High aspect ratio – It defines a structural, mechanical, or aerodynamic component where the length or span considerably exceeds its width, thickness, or diameter. It represents a, slender, elongated, or thin shape, frequently denoted as a ratio (length / diameter or length / width of higher than or equal to 10:1 in applications like MEMS (micro-electro-mechanical systems) or nano-structures.
High aspect ratio micro-structures – These are engineered, three-dimensional features where the vertical height considerably exceeds the lateral width (typically a ratio of 5:1 or higher), designed for improved functionality in micro-electro-mechanical systems (MEMS). These structures, frequently ranging from tens of micro-meters to over a centimeter, need specialized fabrication, such as LIGA (Lithographie, Galvanoformung, Abformung, which translates to Lithography, electroforming, and moulding), deep reactive ion etching (DRIE), or SU-8 lithography, to achieve high-precision, steep-walled, tall features.
High availability – It refers to system design, covering hardware, software, and networks, which ensures operational continuity and high uptime (frequently 99.99 % or more) by minimizing, detecting, and recovering from failures. It focuses on removing single points of failure through redundancy and automated failover to maintain services with little to no downtime.
High bandwidth utilization – It refers to a state where the data transmission rate is close to or exceeds the maximum available capacity of a network or communication channel. It indicates that a high percentage of the total available bandwidth is currently consumed, frequently leading to network congestion, increased latency, and a higher need for efficient data management, such as through advanced modulation or multiplexing.
High capture efficiency – It defines the effectiveness of a system in trapping a high percentage—typically 90 % or higher, of targeted emissions, particles, or materials from a source. It is a measure of performance (e.g., in carbon capture or aerosol, pollution control) which directly influences operating costs, where higher efficiency normally needs more energy and larger equipment.
High-carbon alloy steels – These are ferrous alloys typically containing 0.6 % to 1 % (or up to 1.5 %) carbon, combined with additional alloying elements (e.g., manganese, chromium, nickel) to improve mechanical properties. They are defined by high hardness, high tensile strength, and excellent wear resistance, frequently processed through quenching and tempering to achieve high-strength wires, tools, and spring materials.
High carbon content – It normally refers to ferrous metals, specifically steel, containing a high percentage of carbon, which is added to considerably increase strength, hardness, and wear resistance. It is typically in steel higher than 0.60 % (frequently ranging from 0.61 % to 1.5 %).
High-carbon ferro-chrome (HC Fe-Cr) – It is an important alloying agent for producing stainless steel, alloy steels, and foundry products. It is an iron-chromium alloy, typically produced by the carbo-thermic reduction of chromite ore in submerged arc furnaces (SAF). High-carbon ferro-chrome has a higher content of chromium than charge chrome and is being produced from higher grade of the chromite ore. It has carbon content ranging from 6 % to 8 %.
High-carbon ferro-manganese (HC Fe-Mn) – This alloy contains 75 % to 80 % of manganese, 7.5 % of carbon and 1.2 % of silicon. It is normally used in the iron and steel industry as deoxidizer, fixer of sulphur and alloying agent. It can be made in blast furnace and in electric submerged arc furnace (SAF). In submerged arc furnace it is made by two different practices namely (i) high manganese slag practice, and (ii) discard slag practice.
High-carbon low-alloy steels – These are materials containing 0.6 % to 1.5% carbon, combined with less than 5 % total alloying elements (such as chromium, nickel, molybdenum, and manganese). They offer high hardness, wear resistance, and high-strength, frequently processed through quenching and tempering to form martensite or bainite structures, normally used for springs, cutting tools, and structural wires.
High carbon steels – These steels have carbon content ranging from 0.61 % to 1.5 % with the manganese content ranging from 0.30 % to 0.90 %. The more carbon that is dissolved in the iron, the less formable and the tougher the steel becomes. High-carbon steel’s hardness makes it suitable for plough blades, shovels, bedsprings, cutting edges, or other high-wear applications.
High centrifugal force – It refers to the intense, outward-directed pseudo-force acting on mass particles in high-speed rotating systems (e.g., above 10,000 revolutions per minute), calculated as Fc = r x m x w-square, or (m x v-square)/r. It is used to dramatically accelerate separation, filtration, and mixing by improving settling rates, surpassing gravity by factors of thousands (g-force).
High-chromium cast iron – It is a specialized class of abrasion-resistant white cast iron containing 11 % to 30 % chromium and 1.8 % to 3.6 % carbon, frequently featuring minor alloying elements like manganese, nickel, and molybdenum. Engineered for extreme wear resistance, high-chromium cast iron replaces continuous Fe3C cementite with isolated, harder M7C3 chromium-carbides in a martensitic or austenitic matrix, offering superior hardness (600 BHN to 800 BHN) and corrosion resistance.
High-chromium cast iron rolls – These rolls are high-hardness (frequently higher than Rockwell hardness scale C, HRC 45), wear-resistant, and corrosion-resistant alloys containing 12 % to 30 % chromium and 1.8 % to 3.6 % carbon. They possess a microstructure dominated by hard, discontinuous M7C3 eutectic carbides in a martensitic or austenitic matrix. Widely used in hot strip mills/ cold strip mills and plate mills, they offer superior toughness and abrasion resistance compared to conventional white cast irons.
High coding gain – It is the substantial reduction in the needed signal-to-noise ratio (SNR) to achieve a specific bit error rate (BER) by using error-correcting codes, compared to an uncoded system. It measures the efficiency of ’forward error correction’ (FEC) in improving data reliability over noisy channels without increasing transmit power.
High-conductivity copper – It is the copper which, in the annealed condition, has a minimum electrical conductivity of 100 % IACS (International Annealed Copper Standard). High conductivity copper is a term to describe copper which is exceptionally effective at conducting electricity. It is a versatile material, which means it has a wide variety of functions and applications. High conductivity copper, e.g., is most frequently used to make electrical items, such as cords or outlets. Depending on the need of the product it is being used to create, the material is either very low in oxygen content or completely free from oxygen. Additionally, materials made from high conductivity copper are resistant to corrosion, making it ideal for products which need require durability.
High cooling rate – It refers to the rapid reduction of a material’s temperature, normally during manufacturing processes like quenching, welding, or casting, frequently exceeding 10 deg C per second or higher, resulting in fine-grained micro-structures and increased hardness. It inhibits phase transformations such as diffusional transformation, allowing for the formation of martensite or bainite.
High-current applications – These applications involve systems managing substantial electron flow (high amperes) to drive heavy machinery, automotive, or industrial processes, frequently at low voltage. These applications need robust, specialized components, such as contactors, heavy-duty connectors, and thick conductors, to manage heat dissipation and prevent damage.
High current density – It defines a condition where a large magnitude of electric current flows through a small cross-sectional area of a conductor or electrode, typically measured in amperes per square meter or milli-amperes per square centimeters. It shows a high concentration of charge flow, leading to substantial heating and potential component failure.
High-cycle fatigue – It is the fatigue which occurs at relatively large numbers of cycles. The arbitrary, but normally accepted, dividing line between high-cycle fatigue and low-cycle fatigue is considered to be around 10 to the power 4 cycles to 10 to the power 5 cycles. In practice, this distinction is made by determining whether the dominant component of the strain imposed during cyclic loading is elastic (high cycle) or plastic (low cycle), which in turn depends on the properties of the metal and on the magnitude of the nominal stress. High-cycle fatigue is controlled mainly by crack initiation behaviour of the material, as opposed to crack growth behaviour.
High-definition forgings – These are also called high precision forgings, These forgings refer to specialized, high-accuracy components produced through advanced closed-die (impression-die) forging techniques which result in near-net or net shapes with minimal to no subsequent machining needed. They are designed to meet strict dimensional tolerances and have superior surface finishes.
High-density fibre-board – It is a wood product fabricated by compressing refined wood fibres, resins, and wax under high temperature and pressure, typically achieving a density exceeding 800 kilo-grams per square meter. Renowned for its superior strength, uniform composition, and smooth surface, high-density fibre-board (HDF) is superior to medium density fibre-board (MDF) and ideal for heavy-duty applications.
High-density inclusions – These are mainly resulted by high density refractory metal elements. The known high-density inclusions can be classified into two categories: refractory metal elements (tungsten, molybdenum, tantalum, and niobium etc.) and their compounds (tungsten carbide, and titanium-tungsten etc.).
High density poly-ethylene (HDPE) – it is the resin of choice in blow moulding since it is stiff, chemical resistant, has good processing behaviour and good environmental stress crack resistance.
High deposition rate – It refers to a process where material (metal, coating, or film) is applied to a substrate at an accelerated speed, typically measured in kilograms per hour for welding or micro-meter per hour for thin films. This approach maximizes productivity and reduces production costs but frequently needs strict optimization of process parameters, such as increased current, wire feed speed, or, in the case of manufacturing, high-power plasma, to avoid compromising material quality, integrity, or structure.
High dielectric constant (k) – It refers to a material’s high ability to polarize and store electrical potential energy within an electric field compared to a vacuum. Iit measures a material’s capacity to increase capacitance, allowing for smaller, higher-capacity components in micro-electronics, such as high-κ gate dielectrics in transistors.
High-dimensional probability – It is a field of probability theory, statistics, and engineering which analyzes random vectors, matrices, and structures in high-dimensional spaces. It focuses on asymptotic, non-probabilistic, and quantitative analysis, leveraging concentration inequalities to understand how complex, high-dimensional data behaves.
High dislocation density – It refers to a, high concentration of line defects (typically 10 to the power 12 to 10 to the power 16 per square meter or meter per cubic meter) within a crystalline material’s lattice, normally induced by plastic deformation like cold working. This micro-structure considerably increases yield strength through dislocation forest hardening but frequently reduces ductility and fatigue resistance, though it can improve both strength and ductility in specially engineered alloys.
High duty refractories – These are a type of refractory material designed to withstand high temperatures, typically up to 2,000 deg C, without significant degradation in their structural integrity or chemical properties. They are essential components in several high-temperature industrial applications like steelmaking, where they are used to line furnaces, kilns, and other equipment. High duty refractories have PCE (pyrometric cone equivalent) value ranging from 30 to 33. These refractories are characterized by their ability to maintain their strength and resist deformation at high temperatures. This makes them suitable for applications where other materials fail.
High-efficiency particulate air (HEPA) filter – It is also known as a high-efficiency particulate arresting filter. It is an efficiency standard of air filters. Filters meeting the high efficiency particulate air standard are to satisfy certain levels of efficiency. Common standards need that a high efficiency particulate air filter is required to remove, from the air which passes through, at least 99.95 % of particles whose diameter is equal to 0.3 micrometers, with the filtration efficiency increasing for particle diameters both less than and higher than 0.3 micrometers. High efficiency particulate air filters capture pollen, dirt, dust, moisture, bacteria (0.2 micrometers to 2 micrometers viruses (0.02 micrometers to 0.3 micrometers), and sub-micron liquid aerosol (0.02 micrometers to 0.4 micrometers).
High elastic recovery – It is the capability of a material, such as polymers, elastomers, or metals, to return to its original shape and dimensions after the removal of a deforming load. It shows high resistance to permanent deformation and is important for materials subjected to repeated stretching, compression, or bending.
High electrical conductivity – It is the measure of a material’s inherent ability to allow electric charge (electrons) to flow freely through its lattice structure, characterized by low resistivity. It represents high efficiency in transporting current, important for power transmission and electronic components. Examples include copper, silver, and aluminum.
High electric field – It refers to an intense electro-static field (E = F/Q, measured in volts per meter which approaches or exceeds the dielectric strength of the insulating medium, leading to phenomena like dielectric breakdown, ionization, corona discharge, or non-linear transport. It is characterized by high-density flux lines, frequently used to induce rapid physical / chemical changes in materials.
High-electron-mobility transistor – It is also known as heterostructure field effect transistor (FET) or modulation-doped field effect transistor, is a field-effect transistor incorporating a junction between two materials with different band gaps as the channel instead of a doped region.
High energy ball milling – It is a powder processing technique which uses high-intensity collisions from grinding media (steel / ceramic balls) to break down, weld, and deform material particles. It is mainly used to produce nano-structured materials, induce solid-state alloying, and synthesize metastable phases by creating extreme defect density and grain refinement.
High energy efficiency – It consists of maximizing the ratio of useful energy output to total energy input, reducing waste heat, and minimizing energy consumption for a given task or performance level. It involves optimizing systems to provide the same or better service (e.g., cooling, computing, lighting) while consuming less power, ultimately improving sustainability and reducing operational costs.
High-energy ion beams – These are frequently generated through accelerators like cyclotrons, involve particles with substantial kinetic energy (typically 0.1 mega electron volt to 1 mega electron volt or higher) used for material modification, implantation, and analysis. They feature high linear energy transfer (LET), altering surface and interface properties through deep, controlled penetration.
High energy process – It refers to manufacturing or material processing techniques which apply, release, or transfer large quantities of energy, chemical, electrical, or thermal, over a very short duration or high velocity to deform, synthesize, or manipulate materials. These processes are designed for high-efficiency forming, joining, or treating complex and hard-to-form materials.
High-energy-rate compacting – It consists of compacting a powder at a very rapid rate by the use of explosives in a closed die.
High-energy-rate compaction – It frequently referred to as ‘high-velocity compaction (HVC) or dynamic compaction in powder metallurgy. is a specialized densification process where metal powders are consolidated using extremely high velocities (typically around 200 meters per second) and high-pressure waves, rather than the slow, static pressure used in conventional press-and-sinter methods.
High-energy-rate forging – It is a closed-die hot-forging or cold-forging process in which the stored energy of high-pressure gas is used to accelerate a ram to unusually high velocities in order to effect deformation of the work-piece. Ideally, the final configuration of the forging is developed in one blow or, at most, a few blows. In high-energy-rate forging, the velocity of the ram, rather than its mass, generates the major forging force.
High-energy-rate forming – It is group of forming processes which applies a high rate of strain to the material being formed through the application of high rates of energy transfer.
High energy storage density – It refers to the quantity of energy which can be stored per unit volume or mass, with gasoline and diesel fuels showing very high energy storage densities compared to electric energy storage systems like advanced batteries.
High engine speed – It refers to an engine’s operation at high revolutions per minute (rpm), where it produces peak power but faces increased thermal and mechanical stress. It indicates rapid rotational movement of the crankshaft, important for achieving maximum power output.
High-entropy alloys – These alloys are a class of materials which contain multiple principal elements in nearly equimolar proportions, resulting in unique mechanical, physical, and chemical properties. They are characterized by solid solution strengthening and increased entropy, making them suitable for applications needing high strength, corrosion resistance, and thermal stability.
Higher binder force – It is also called high blank holder force. It refers to an increased, frequently intensified, mechanical pressure applied to the flange of a sheet metal blank during deep drawing or stamping. The main objective of a higher binder force is to restrict the flow of material into the die cavity, improving material tension to reduce spring-back, manage complex geometries, and prevent wrinkling.
Higher heating value – It is also known as the gross calorific value (GCV). It is defined as the total energy released when a substance is burned in an oxygenated atmosphere and the beginning and end of the reaction are at room temperature. It represents the total quantity of heat released when a fuel is completely burned, with the water produced by the combustion condensed back to a liquid state.
Higher order boundary element method – It is an advanced numerical technique for solving partial differential equations by discretizing only the boundary of a domain. Unlike constant or linear BEM (boundary element method,), higher order boundary element method uses high-order polynomial functions to describe geometry, boundary conditions, and unknown variables, resulting in increased accuracy, smoother results, and fewer elements for complex geometries in fields like acoustics, fluid-structure interaction, and wave-body interaction.
Higher-order derivatives – These are a fundamental concept representing the derivative of a function taken multiple time. While the first derivative, f’(x) or dy/dx, measures the rate of change or slope, higher-order derivatives provide deeper insights into the behaviour of systems, such as curvature, concavity, acceleration, and jerk.
Higher order dynamic mode decomposition – It is an advanced, data-driven modal decomposition technique extending standard DMD (dynamic mode decomposition) to analyze complex, non-linear, and noisy dynamical systems. By incorporating d – 1 time-lagged snapshots, higher order dynamic mode decomposition overcomes standard DMD limitations in capturing non-stationary dynamics and high-frequency oscillations, providing improved, sparse, and low-dimensional representations.
Higher-order Laue zones (HOLZ) – These are peripheral, ring-shaped diffraction spots in electron diffraction patterns, specifically transmission electron microscopy (TEM) and ‘convergent-beam electron diffraction (CBED), representing planes with high Miller indices (h, k, l) not in the Zeroth-Order Laue Zone. Defined by the equation ‘hu+ kv + lw = N’ (where N is higher than 0 is the zone order), HOLZ lines are highly sensitive to lattice parameter variations (sensitivity around 0.0002 nano-meters), used for precise local stress / strain measurements.
Higher order modulation – It is a technique in digital communications which increases data rates and spectral efficiency by packing more bits into each signal symbol. It uses complex, high-density signal constellations, e.g., 16-QAM, 64-QAM, 256-QAM (quadrature amplitude modulation) to transmit, for example, 4, 6, or 8 bits per symbol instead of lower-order modulation like QPSK-2 bits (quadrature phase shift keying).
Higher-order shear deformation plate theory – It is a framework which improves upon ‘first-order shear deformation theory’ (FSDT) by assuming a non-linear (typically parabolic) distribution of transverse shear strains across a plate’s thickness. It ensures zero shear stress at the top and bottom surfaces, eliminating the need for shear correction factors.
Higher order statistics – It refers to analysis methods utilizing third-order or higher moments and cumulants to characterize non-Gaussian, non-linear, or non-stationary signals. Unlike second-order statistics (auto-correlation / variance), higher order statistics (HOS) preserves phase information, suppresses Gaussian noise, and identifies true statistical independence, making them necessary for advanced signal processing, system identification, and pattern recognition.
Higher order theory – It defines a refined analytical framework for analyzing beams, plates, and shells by assuming non-linear (e.g., parabolic) distributions of shear strains / stresses across the thickness. It improves accuracy over lower-order theories by satisfying stress-free surface conditions without needing shear correction factors.
Highest occupied molecular orbital – It is the molecular orbital containing the highest energy electrons in a molecule at absolute zero, acting as the main site for electron donation. A higher ‘highest occupied molecular orbital’ (HOMO) energy indicates higher electron-donating capacity, important for assessing chemical stability, reactivity, and corrosion inhibition.
High field gradients -These refer to regions of steeply changing magnetic field strength, typically created by ferro-magnetic matrices (e.g., meshes, rods) within a strong background field, frequently exceeding 1 Tesla to 2 Tesla. These systems improve magnetic force on fine, weakly magnetic particles, widely applied in high-gradient magnetic separators (HGMS) for mineral processing, water purification, and waste recycling.
High fixed costs – These costs refer to substantial, upfront, and ongoing expenditures, such as machinery, facility rent, research and development, and salaries, which remain constant regardless of production output levels. These non-variable expenses are critical in heavy manufacturing and infrastructure projects, frequently acting as high barriers to entry.
High-fracture toughness steels – These are engineering alloys designed to resist brittle fracture and crack propagation under stress, specifically characterized by high resistance to crack growth (Kic), often achieved through a microstructural blend of tempered martensite, retained austenite, and bainite. They are crucial for demanding applications (e.g., aerospace, automotive, infrastructure) needing durability under high-stress concentrations.
High frequency – It normally refers to alternating current (AC) or electro-magnetic waves oscillating between 3 mega-hertz and 30 mega-hertz (radio spectrum), though in modern electronics, it frequently implies frequencies up to 300 giga-hertz (micro-wave range and above). These signals are characterized by short wave-lengths, enabling compact antenna design and high-speed data transmission.
High-frequency approximation – It is a technique used to analyze wave propagation, scattering, or dynamic systems when the wave-length is much smaller than the physical dimensions of the object or system. It simplifies complex wave equations by assuming rays or paths, frequently treating problems with geometric optics, physical optics, or asymptotic expansions.
High-frequency butt welding – It is a solid-state resistance welding process which joins metal edges by inducing high-frequency current (typically 50 kilo-hertz to 400 kilo-hertz) to rapidly heat surfaces through skin and proximity effects, followed by pressure application. It creates high-strength joints in pipes and, specifically, in long straight butt seams at high production speeds.
High-frequency component – It refers to electronic parts (inductors, capacitors, printed circuit boards) or signal elements designed to operate where electrical characteristics are dominated by rapid signal changes, typically above 1 giga-hertz or when circuit dimensions are comparable to the wavelength. These components minimize loss and manage parasitic inductance / capacitance, using specialized materials like Teflon.
High-frequency content – It refers to the rapid, small-scale variations in a signal, image, or structure, typically representing sharp edges, fast transients, noise, or fine details. It shows rapid changes in intensity or amplitude, frequently analyzed using Fourier transforms to identify high-spectral components.
High-frequency eddy current – It is a non-destructive testing technique using electro-magnetic induction at frequencies typically between 100 kilo-hertz and 100 mega-hertz to induce shallow surface currents in conductive materials. Because of the strong skin effect, high-frequency eddy current provides high sensitivity for detecting surface defects and characterizing low-conductivity or thin materials.
High frequency electronics – It refers to electronic devices and systems which operate at high frequencies, typically in the microwave range and above, including applications such as cellular phones, satellite navigation, and wireless communication technologies. These devices rely on a deep understanding of electro-magnetic fields and are important for advancing modern communication systems.
High-frequency induction – It is a process which uses a high-frequency alternating magnetic field, typically higher than 100 kilo-hertz, to induce eddy currents within a conductive material, generating rapid, non-contact, and localized heat through Joule heating. It is normally used for precise, shallow surface hardening, brazing, and welding, with higher frequencies yielding shallower, faster heating.
High frequency induction welding – It is an automated, high-speed joining process which uses electro-magnetic induction (typically 200 kilo-hertz to 600 kilo-hertz) to generate localized resistance heat on metal surfaces. An induction coil induces eddy currents, heating edges to welding temperature before pressure rolls forge them into a solid-state weld, commonly used for pipe/tube production.
High frequency electric resistance welding process – The process is used for the production of welded pipes. The process involves application of high frequency alternating current in the range of 200 kilo hertz to 500 kilo hertz. The pipe forming and energy input operations are performed by separate units. The strip is shaped in a roll forming mill or in an adjustable roll stand (natural function forming) into an open seam pipe for a wide range of pipe products. These include line pipes and structural pipes in the size ranges of around 20 millimeters to 600 millimeters outer diameter and wall thickness range of 0.5 millimeters to 16 millimeters and pipe blanks for a downstream stretch-reducing mill. The starting material is hot rolled wide steel strip or skelp. Depending on the pipe dimension and application, and particularly in case of precision pipes, the steel strip can undergo an upstream pickling operation, or cold rolled strip is used.
High-frequency heating – It is the heating of materials by di-electric loss in a high-frequency electrostatic field. The material is exposed between electrodes and is heated quickly and uniformly by absorption of energy from the electrical field.
High-frequency induction heating – It is a contactless method of heating electrically conductive materials, mainly metals, using electromagnetic induction. It involves generating heat within the material itself by passing a high-frequency alternating current through a coil, creating a magnetic field which induces eddy currents in the work-piece, causing it to heat up. High-frequency induction heating relies on the principle of electromagnetic induction. When a high-frequency alternating current flows through a coil, it generates a rapidly changing magnetic field. This magnetic field, in turn, induces circulating electrical currents (eddy currents) within any nearby conductive material (the work-piece).
High frequency induction quenching – It is a form of heat treatment in which a metal part is heated by induction heating and then quenched. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part. Induction hardening is used to selectively harden areas of a part or assembly without affecting the properties of the part as a whole.
High-frequency induction welding (HFIW) – It is a resistance welding process which uses high-frequency electrical currents to generate heat at the edges of metal workpieces, which are then pressed together to form a weld. This technique is particularly well-suited for joining metal tubes and pipes, and it is characterized by high welding speeds, energy efficiency, and minimal heat-affected zone. High-frequency induction welding utilizes high-frequency alternating current (AC) to induce electrical currents within the work-piece.
High-frequency quenching – It is a surface hardening heat treatment process using electro-magnetic induction (typically 100 kilo-hertz to 500 kilo-hertz) to rapidly heat the surface of steel components to austenitizing temperatures, followed immediately by quenching. It creates a thin, hard, wear-resistant outer layer (1.5 millimeter to 2 millimeters) while maintaining a tough, ductile core.
High frequency reciprocating rig – It is a tool designed to measure the lubricity of fuels and lubricants by assessing friction and wear under high-frequency, low-amplitude oscillating motion. It is the industry standard for evaluating diesel fuel lubricity, measuring wear scar diameter (WSD) on a steel ball against a plate.
High frequency resistance welding – It is a group of resistance welding process variations which uses high frequency welding current to concentrate the welding heat at the desired location.
High-frequency welding – It is a method of welding which generates heat through resistive heating of a current induced in the work-piece, utilizing very high frequencies (e.g., 400 kilo-hertz) to concentrate the current near the surface of the material, allowing for rapid welding with low heat input.
High friction surface treatment – It is a safety application consisting of a specialized pavement overlay, typically high-quality calcined bauxite aggregate bonded by a polymer resin binder, applied to existing roadways. It drastically improves surface micro-texture and macro-texture to improve tire grip, reduce braking distances, and prevent wet-weather skidding in high-risk areas.
High gas flow rate – It refers to gas moving at high velocities, typically causing, or operating near, erosion-prone conditions in equipment. It defines a high volume or mass of gas passing through a cross-sectional area per unit of time (e.g., high litres per minute, or kilograms per second. The movement of gas at substantial velocity and volume, frequently lead to turbulent, high-velocity, or high-pressure regimes. High flow rates are frequently associated with erosion effects on metal equipment in industries.
High gas pressure control – It is a control to stop the burner if the gas pressure is very high.
High grade – It is the rich ore. As a verb, it refers to selective mining of the best ore in a deposit.
High gradient magnetic separators – Several types of high gradient magnetic separators have been developed based on the fact that high magnetic field gradients can produce large magnetic forces. These separators are also called ‘induced pole’ separators because the field gradients are produced by applying a relatively uniform background magnetic field to a ferro-magnetic structure (grids, screens, grooved plates or steel wool) and inducing magnetic poles along properly oriented edges. Since large magnetic field gradients can generally exist only in small volumes these separators are designed for the separation of small magnetic particles. Producing high gradients and large magnetic forces over a surface area large enough to trap practical numbers of particles is a major issue. Needles with their axes parallel to the applied field produce high gradients in relatively low fields but the available trapping surface is very limited. By contrast filaments magnetized perpendiculars to their long axis have a large demagnetizing factor, but much greater surface area.
High impact – It refers to a sudden, high-force collision or dynamic load applied over a very short duration, causing substantial energy transfer, high strain rates, and potential structural deformation. It frequently involves velocities above 25 meters per second, needing specialized design to resist fracture, buckling, or penetration.
High-impact event – It refers to a sudden, high-force collision or shock applied to a structure over a very short duration, typically causing substantial deformation, damage, or structural response. It involves high velocity, high energy (frequently larger than 100 joules), and rapid acceleration, resulting in severe local damage or catastrophic failure.
High impedance node – It is a circuit point with negligible current flow to other nodes, frequently appearing as an open circuit or high resistance (above 600 ohms, frequently mega-ohm range). These nodes are sensitive to noise, hold charge (capacitive storage), and are used to achieve high voltage gain, but are prone to picking up parasitic capacitance and noise, creating substantial, slow-responding poles.
High integration density – It refers to the practice of packing a maximum number of electronic components, mainly transistors, but also resistors, capacitors, and diodes, into the smallest possible physical area or volume. In the context of semiconductors, this is frequently quantified as the number of transistors per unit area.
High integrity castings – These are components manufactured to meet stringent quality standards, characterized by minimal porosity, high density, and superior tensile strength / ductility. They are produced through specialized processes like vacuum die casting, squeeze casting, or low-pressure casting, designed to eliminate gas entrapment and shrinkage.
High integrity pressure protection system – It is an actuated valve and control system to protect against over-pressure of pipeline risers.
High-intensity ultrasonication – It is a process applying high-power sound waves (typically 20 kilo-hertz to 100 kilo-hertz, 10 watts per square centimeter to 1,000 watts per square centimeter) to liquids, inducing acoustic cavitation, the formation, growth, and violent collapse of bubbles. This generates intense localized shear forces, heat, and pressure, used for emulsification, degassing, and nano-particle synthesis.
High interstitial defect – It consists of interstitially stabilized alpha-phase region in titanium of substantially higher hardness than surrounding material. It arises from very high local nitrogen or oxygen concentrations which increase the beta-transus and produce the high-hardness, frequently brittle alpha-phase. Such a defect is frequently accompanied by a void resulting from thermo-mechanical working. These defects are also termed type ‘I’ or low-density interstitial defects, although they are not necessarily of low density.
High ionic strength – It refers to solutions with a high concentration of dissolved ions, creating substantial electrical shielding which reduces inter-ionic attractions and compresses the electrical double layer (EDL) around particles. Higher concentrations and valencies of ions (e.g., Ca2+, Al3+) drastically increase the value. High ionic strength frequently leads to reduced zeta potential, causing colloidal instability, particle aggregation, or flocculation.
High ionization rate – It refers to a process where a large percentage of target material (up to 70 % or more) is converted into ions within a plasma, common in high-power impulse magnetron sputtering (HiPIMS). This condition shows a dominance of metal ions, enabling dense, adherent coating deposition.
High κ dielectrics – These refer to materials with a high relative dielectric constant (κ), such as Ta2O5 (tantalum penta- oxide), TiO2 (titanium di-oxide), and HfO2 (hafnium di-oxide), which are normally used in gate oxide applications in microelectronics because of their superior dielectric properties compared to traditional silicon oxide (SiO2, κ = 3.9). These materials have gained interest for their potential to enhance device performance, although some are not thermodynamically stable in direct contact with silicon.
High kinetic energy – It refers to the immense mechanical energy possessed by an object, fluid, or particle because of its high velocity and / or mass, defined by KE =1/2 m x v-square. It represents the work needed to accelerate a body from rest to its current velocity, frequently causing substantial damage upon impact.
High Knudsen number – It defines a flow regime where the molecular mean free path (lambda) is comparable to or larger than the characteristic physical length scale (L) of the system (Kn =lambda/L), indicating rarefied gas flow where continuum mechanics (Navier-Stokes) fail and individual molecule-wall collisions dominate.
High laser power density – It is the measure of radiant power per unit area (watts per square centimeter or mega-watts per square centimeter) of a focused beam, indicating how intensely energy is concentrated. It is Important for defining material processing efficiency, such as in laser cutting, welding, or ablation, where high density drives rapid, precise melting or vapourization. It is calculated as ‘power density = laser power / spot area’.
High-level requirements – The high-level requirements explain the major requirements and characteristics of the final product, including its purpose as a product and within the organization.
High-level synthesis – It is an automated process which converts high-level, behavioural, or algorithmic descriptions (such as C, C++, or SystemC) into register-transfer level (RTL) hardware description languages. It acts as a bridge between abstract software-like code and hardware implementation, enabling faster design, optimization, and verification for FPGAs (field programmable gate array) or ASICs (application-specific integrated circuit).
High-level waste – It is the radio-active wastes which are highly radio-active materials, normally produced as a by-product of reactions which occur inside nuclear reactors. High-level waste takes one of two forms namely (i) spent (used) reactor fuel when it is accepted for disposal, or (ii) waste materials remaining after spent fuel has been reprocessed. High-level waste is heat-generating and, as a result, the temperature of the high-level waste can rise considerably over time. This has to be taken into account when designing storage or disposal facilities.
High-lighting – It means buffing or polishing selected areas of a complex shape to increase the lustre or change the colour of those areas.
High load carrying capacity – It refers to the maximum force, stress, or weight a component, material, or structural system can withstand without failure, permanent deformation, or loss of functionality. It indicates superior structural integrity under high-intensity, static, or dynamic loading conditions, important for ensuring safety and reliability.
Highly active liquor – It is an intermediary stage in the vitrification process. Strict limits are imposed on the quantities of highly active liquor which can be stored. Highly active liquor consists of components of spent fuel other than uranium (i.e., radio-active by-products) dissolved in concentrated nitric acid after separation by the PUREX process.
Highly active liquid effluent facility – It is made of seismically qualified reinforced concrete and comprises a series of storage tanks used to store radio-active waste arising from nuclear processing operations.
Highly cross-linked poly-ethylene – It is a polymer, typically derived from high-density poly-ethylene (HDPE) or ultra-high molecular weight poly-ethylene (UHMWPE), processed through irradiation or chemical methods (peroxide / silane) to create a 3D network of covalent bonds between molecular chains. This modification considerably increases wear resistance, thermal stability (up to 105 deg C), and environmental stress crack resistance compared to conventional poly-ethylene (PE).
Highly deformed layer – In tribology, it is a layer of severely plastically deformed material which results from the shear stresses imposed on that region during sliding contact.
Highly enriched uranium – It is the uranium which has been modified by increasing the concentration of the fissionable isotope Uranium-235, containing 20 % or more of the isotope Uranium-235. A quantity of highly enriched uranium can be described in terms of either the total mass of all the Uranium isotopes, or as the mass of the fissile isotope Uranium-235, e.g., 100 kilograms of 70 % enriched highly enriched uranium can also be described as 70 kilograms Uranium-235.
Highly exothermic reaction – It is a chemical process releasing substantial heat (dH below zero), posing safety risks and needing, e.g., intensive heat removal, temperature profiling, or specialized reactor designs to manage rapid rates and prevent thermal runaway.
Highly oriented pyrolytic graphite – It is an ultra-high purity, synthetic form of graphite characterized by a highly ordered, layered structure with a mosaic spread angle of less than 1 degree. It is produced by stress-annealing pyrolytic graphite at extreme temperatures (around 3,300 K) and high pressure, resulting in aligned graphene sheets.
High Mach number – It normally refers to speeds where compressible flow effects are dominant, starting in the supersonic range (M above 1.3) and extending into hypersonic regimes (M above 5). It represents the ratio of object velocity to the local speed of sound, characterized by substantial shock waves, rapid drag increase, and intense aerodynamic heating.
High mass flux – It is defined as a high rate of mass flow per unit cross-sectional area (kilograms per second per square meter), representing the quantity ‘G = d x v’ (density x velocity). It indicates intense, frequently turbulent, flow which improves heat transfer, frequently leading to annular-dispersed flow patterns and high critical heat flux (CHF) in thermal-hydraulic systems.
High melting point – It defines a material (normally a metal, ceramic, or alloy) which retains solid-state structural integrity and mechanical properties at extremely high temperatures, typically starting well above 1,000 deg C to 1,500 deg C. These materials, frequently including refractory metals like tungsten (3,422 deg C), feature strong inter-atomic bonds and are important for applications needing resistance to heat, wear, and thermal deformation.
High mobility channel materials – These are advanced semiconductors, e.g., Ge (germanium), SiGe (silicon-germanium), III-V compounds like InGaAs (indium-gallium-arsenide), GaN (gallium nitride), utilized in place of traditional silicon to considerably improve carrier mobility (speed) in CMOS (complementary metal-oxide-semi-conductor) devices. These materials enable lower power, higher performance transistors by increasing charge carrier velocity in response to electric fields, important for logic devices at less than or equal to 10 nano-meters nodes.
High mobility materials – These are advanced semiconductors, e.g., Ge (germanium), SiGe (silicon-germanium), III-V compounds like InGaAs (indium-gallium-arsenide), GaN (gallium nitride), designed to show considerably higher electron or hole velocity with minimal scattering compared to silicon, essential for high-performance, low-power CMOS (complementary metal-oxide-semi-conductor) devices at below nano-meters nodes. They reduce heat dissipation and increase operating frequency, frequently in HEMTs (high-electron-mobility transistor), by using engineered heterojunctions or strained layers.
High modulus polyethylene fibre – It is an ultra-high-strength, low-density fibre produced from ultra-high molecular weight polyethylene (UHMWPE) through a gel-spinning process. It is characterized by extremely long molecular chains, offering a high-tensile modulus (frequently 34 giga-pascals to 200 giga-pascals), 15 times higher abrasion resistance than carbon steel, and low weight.
High moisture absorption – It refers to a material’s significant tendency to absorb water molecules from its environment, frequently resulting in swelling, decreased strength, and degraded mechanical properties. Common in polymers, composites, and natural fibres, this process is quantified as a percentage weight gain (above 1 % for substantial, up to 7 % for nylon).
High-molecular-weight polymers – These are macromolecules composed of long chains of repeating monomer units, normally defined as having a number average molecular weight (Mn higher than or equal to 1,000 grams per mol, frequently reaching into the hundreds of thousands or millions. These engineering materials are used for their high toughness, abrasion resistance, and tensile strength.
High-nickel alloys – These are metallic materials containing above 30 % nickel (frequently 64 % to 70 % or more), alloyed with elements like chromium, molybdenum, and copper to provide exceptional corrosion resistance, high-temperature strength, and ductility. These base-nickel alloys are designed for extreme environments (aerospace, chemical, marine) because of their oxidation resistance and metallurgical stability.
High oil temperature control – It is a control to stop the burner if the oil temperature is very high.
High operating temperature – It refers to environmental or system conditions exceeding standard design thresholds (typically above 125 deg C for electronics or above 800 deg C for specific fuel cells), where materials risk degradation, such as creep, oxidation, or reduced mechanical strength. It indicates temperatures close to a material’s melting point (t is 0.6 in Kelvin).
High oxygen activity – It normally refers to a state where oxygen is present at a high thermodynamic potential, creating a strong driving force for oxidation, chemical reactions, or degradation. It is frequently distinguished from mere oxygen concentration, as it describes the tendency of oxygen to react with its surroundings.
High oxygen partial pressure (pO2) – It refers to an increased concentration or high absolute pressure of oxygen within a gas mixture, calculated as the mole fraction of oxygen multiplied by the total pressure (Pi = Xi x Ptotal). It is used to improve mass-transfer driving forces in systems like fermentation or fuel cells.
High oxygen potential – It refers to an environment’s high capacity to facilitate the oxidation of materials, frequently characterized by a high partial pressure of oxygen (pO2) or a high Gibbs free energy for oxidation. It is an important parameter which determines the oxidation-reduction state of systems.
High-pass filter – It is an electronic circuit or signal processing algorithm which allows signals with frequencies higher than a specific cut-off frequency to pass through while attenuating (reducing the amplitude of) signals with frequencies below that cut-off. It acts as a low-cut filter, normally used in audio (removing bass / noise), RF (radio frequency) communication (blocking direct current), and image processing.
High packing density – It defines the ratio of solid particle volume to the total bulk volume, aiming to minimize void space for improved material performance. It represents an optimal arrangement of particles (e.g., in concrete, powder, or electronics) where smaller particles fill voids between larger ones, reducing porosity and maximizing, typically through packing, structural integrity.
High-pass filter – It is an electronic circuit or algorithm which allows signals with frequencies higher than a specific cutoff frequency (fc) to pass through while attenuating (reducing the amplitude of) signals with lower frequencies. Normally used in audio (bass-cut), RF (radio frequency) communication, and signal processing, it acts as a frequency-dependent voltage divider, often implemented using RC (resistor-capacitor) or RL (resistor-inductor) components.
High-performance – It refers to the design, development, and manufacturing of materials, systems, or processes which deliver superior, specialized, or, in several cases, extreme, functional results beyond conventional, industry-standard capabilities. It focuses on improving strength, durability, efficiency, or speed, such as in high-performance materials or computing systems.
High performance anion exchange chromatography – It is an advanced liquid chromatography technique which separates charged molecules (mainly anions like saccharides) based on their ionic interactions with a specialized, positively charged resin. Engineering applications utilize high-pH conditions and high-performance, frequently polymeric, stationary phases to achieve superior resolution, high throughput, and sensitivity, particularly in downstream processing.
High-performance concrete – It is engineered to exceed the strength, durability, and workability of conventional concrete, typically utilizing a low water-to-cement ratio (less than or equal to 0.35), high-quality aggregates, and admixtures like silica fume. It offers exceptional durability, high compressive strength (frequently higher 70 mega-pascals to 80 mega-pascals), and low permeability for demanding infrastructure projects.
High-performance fibres – These are synthetic or inorganic materials designed with exceptional strength, high modulus, and superior resistance to heat, chemicals, or fire, far exceeding conventional fibres like polyester or nylon. Typically defined by a tenacity higher than 20 grams per danier, these specialized fibres are used in critical applications like structural reinforcement.
High performance grinding – It is the applications of high-speed grinding (HSG) which have expanded the field of grinding from traditional finishing operation to now more widely employed high-performance machining. In this way, process development has led to a new grinding paradigm, which refers to the configuration of improved process with high-performance capabilities. In this way, high-performance grinding corresponds to the dual attributes of high-efficiency and high-precision, which are needed for competitive grinding processes.
High-performance liquid chromatography – It is formerly referred to as high-pressure liquid chromatography. It is an advanced analytical technique used to separate, identify, and quantify components in a mixture, relying on high-pressure pumps to pass a liquid solvent (mobile phase) through a column containing a stationary phase. It is a refined, high-speed, and automated version of column chromatography, normally used in environmental science to analyze non-volatile or thermally unstable compounds.
High performance liquid chromatography-mass spectrometry – It is an analytical technique combining high-pressure, column-based liquid chromatography separation with the molecular identification capabilities of mass spectrometry. It separates complex mixtures through a stationary phase and quantifies / identifies compounds based on mass-to-charge ratios, offering high sensitivity and rapid, automated analysis for chemical samples.
High-performance steel – It is a steel grade with superior mechanical properties compared to conventional structural steel, characterized by high yield strength (typically above 450 mega-pascals to 460 mega-pascals), exceptional fracture toughness, excellent weldability, and improved corrosion resistance. Designed for infrastructure like bridges and buildings, it reduces material usage and boosts construction efficiency.
High peripheral speed – It refers to the high linear velocity (typically meter per second or meter per minute) of a point on the outer edge or circumference of a rotating component, such as a cutter, impeller, or wheel. It is important for maximizing material removal rates, efficiency in cutting or grinding, and influencing mixing shear rates.
High-permeability reservoirs – These are geological formations with high fluid conductivity (typically above 100 milli Darcy to 1,000 milli Darcy), allowing for rapid fluid movement, high production rates, and efficient recovery. Defined by well-connected, large pore throats, these reservoirs improve economic viability by minimizing flow resistance but need careful management to avoid premature water or gas breakthrough.
High photon energy – It refers to electro-magnetic radiation with high frequencies, short wavelengths (X-rays, gamma rays), and high kinetic energy (E = h x f), typically measured in electron-volts (eV) or joules. These photons are characterized by their ability to ionize atoms, eject inner-shell electrons, and penetrate materials, normal used in imaging, and spectroscopy.
High power amplifier – It is an electronic device designed to amplify a low-power signal to a high-power level (high voltage and current) to drive loads like antennas or speakers, normally serving as the final, high-efficiency stage in communication systems or audio equipment. These amplifiers, frequently using specialized, larger transistors, prioritize delivering maximum power, frequently in the order of watts, to a load with high power conversion efficiency.
High-power diode lasers – These lasers are semiconductor devices emitting, typically in the near-infrared (808 nano-meters to 980 nano-meters), with power levels ranging from several watts to kilowatts. They are characterized by high electro-optical efficiency, compact size, and reliability, frequently utilizing GaAs (gallium-arsenide)-based materials. Engineered for direct material processing, welding, and pumping solid-state lasers, high-power diode lasers stack diode bars for high output, providing efficient, direct electrical-to-optical conversion.
High power electronics – It is a field focused on the application of solid-state electronics to convert, control, and manage high-voltage and high-current electrical power. It bridges electrical energy sources and loads by using semiconductor switches, such as diodes, thyristors, MOSFETs (metal–oxide–semiconductor field-effect transistor), IGBTs (insulated-gate bipolar transistor) to efficiently alter power forms, insulated-gate bipolar transistor, alternating current / direct current, direct current / alternating current, direct current / direct current, or alternating current / alternating current, with minimal energy loss.
High power impulse magnetron sputtering – It is a PVD (physical vapour deposition) thin-film coating technique using extremely high, short-duration power pulses (kilo-watts per square centimeter) to create a highly ionized metal plasma. By operating at low duty cycles, it prevents target overheating, resulting in denser, smoother, and better-adhered films compared to conventional direct current sputtering. The process achieves a high degree of ionization of the sputtering material, allowing for better control over the coating structure via ion bombardment
High pressure ammonia liquor aspiration system – The high-pressure ammonia liquor aspiration system is effective for controlling charging emissions in coke oven batteries. In this system, the ammoniacal liquor, which is a byproduct, is pressurized to around 35 kilograms per square centimeter to 40 kilograms per square centimeter and injected through special nozzles provided in the goose neck at the time of charging. This creates sufficient suction inside the oven thereby retaining the pollutants from being released to the atmosphere. The system consists of high-pressure multistage booster pumps, sturdy pipe work, specially designed spray nozzles, suitable valves, and control instruments. This system emissions control results in saving in quantity of process steam and increase in the yield of raw gas.
High pressure briquetting process – It is the process in which the pressure applied is above 100 MPa. This process uses a heating device and the process is normally carried out for materials having inherent binders (lignin) and hence no external binder is used. However, some of the materials need binders even under high pressure conditions.
High-pressure consolidation – It is a powder processing technique which uses extremely high compressive forces (frequently combined with high temperatures) to densify metal powders or porous materials into solid, bulk components. It is frequently used in severe plastic deformation (SPD) methods, such as high-pressure torsion (HPT) or spark plasma sintering (SPS), to produce nano-structured, ultra-fine grained, or amorphous materials with high strength and near-theoretical density.
High-pressure die casting – It is a metal casting process where molten metal is injected into a die cavity under high pressure and at high speed, resulting in the creation of precise, complex, and high-quality metal parts. This process is normally used for mass production of non-ferrous metal components, particularly in industries like automotive and electronics.
High-pressure gas quenching – It is a, frequently vacuum-based, metallurgical heat treatment process which rapidly cools heated, typically alloyed, steel parts using high-velocity, compressed gas (normally nitrogen or helium) to achieve high surface / core hardness. It provides superior dimensional control and distortion reduction compared to liquid quenching by eliminating oil-related uneven cooling and burnout.
High pressure and high temperature – It normally define environments with bottom-hole temperatures exceeding 150 deg C and pore pressures exceeding 69 mega-pascals. These conditions necessitate specialized equipment, such as blowout preventers (BOPs) rated above 69 mega-pascals.
High pressure common rail – It is an advanced direct-injection fuel system for diesel engines which decouples fuel pressurization from injection timing. It uses a single high-pressure reservoir (‘rail’) to store fuel at up to 250+ mega-pascals to supply multiple injectors. This enables precise, flexible, multiple injection events per cycle, improving fuel atomization, improving combustion efficiency, and considerably reducing emissions.
High-pressure conditions – These typically refer to environments or systems operating well above atmospheric pressure (above 0.1 mega-pascal), frequently ranging between 0.1 mega-pascal to 100 mega-pascals for industrial processes like synthesis. These conditions considerably alter material properties, fluid behaviour, and reaction kinetics, needing specialized equipment such as autoclaves, reactors, or diamond anvil cells.
High pressure die casting – It is a high-speed manufacturing process which forces molten non-ferrous alloys (aluminum, zinc, magnesium) into reusable steel moulds (dies) under high pressures (typically 10 mega-pascals to 170 mega-pascals). It produces complex, thin-walled, dimensionally accurate parts with high production rates, low porosity, and excellent surface finish, making it ideal for automotive and aerospace components
High-pressure generator – It is a device or system designed to create, amplify, or maintain extreme fluid pressures (liquid or gas) for applications like material testing, hydraulic fracturing, or power generation. These systems frequently utilize hydraulic pumps, boosters, or pistons to achieve rapid pressure jumps, such as in water-hammer simulation.
High-pressure generator engineering – It focuses on designing systems which produce, boost, or manage fluids (liquids / gases) at high pressures, normally utilizing piston pumps, PEM (proton exchange membrane) electrolysis, or membrane technology to achieve pressures up to 415 mega-pascals. Key applications include industrial hydrogen generation (up to 1.5 mega-pascals), high-pressure nitrogen (up to 35 mega-pascals), hydro-demolition, and hydraulic impulse tests.
High-pressure laminates – These are laminates moulded and cured at pressures not lower than 6.9 MPa, and normally in the range of 8.3 mega-pascals to 13.8 mega-pascals.
High pressure homogenization – It is a technique which forces liquids through narrow gaps at pressures between 15 mega-pascals and 400 plus mega-pascals, creating intense shear, turbulence, and cavitation. It is mainly used to reduce particle size, produce stable emulsions, disrupt cell structures for sterilization, and modify materials in several applications.
High-pressure membranes – These are advanced, pressure-driven filtration technologies, specifically ‘reverse osmosis ‘(RO) and ‘nano-filtration’ (NF), used to separate dissolved solids, ions, and contaminants from liquids, typically at pressures above 1 mega-pascal. They feature dense, non-porous polyamide layers which remove molecules by diffusion.
High-pressure oil – It focuses on managing pressurized oil systems (above 100 mega-pascals in some applications) for lubrication, fuel injection, and hydraulic power, ensuring operational longevity and safety in engines and industrial machinery. It involves specialized pumps, corrosion-resistant components, and strict adherence to pressure vessel codes
High-pressure mould – It is a specialized, automated manufacturing process where molten metal, normally non-ferrous alloys like aluminum or zinc, is forced under intense pressure (higher than 7 mega-pascals to 1,000 mega-pascals) into a permanent, hardened steel die cavity, resulting in high-volume, precise, and complex parts with superior surface finishes.
High-pressure moulding – It is a term which is applied to certain types of high-production sand moulding machines in which high-pressure air is instantly released from a large pressure vessel to produce extremely hard, high-density moulds from green sand.
High pressure operation, blast furnace – One of the limiting factors in attempting to increase the blast volume rate in the blast furnace is the lifting effect that is caused by the large volumes of gases blowing upward through the burden. This lifting effect (the mass flow rate) prevents the burden from descending normally and causes a loss rather than an increase in production. To increase production rates above normal, the blast furnace is equipped with septum valve in the top gas system to increase the exit gas pressure. This increase in pressure compresses the gases throughout the entire system and permits a larger amount of air blast to be blown. With this increase in the quantity of air blown per minute, there is a corresponding increase in production rate. In addition, this also suppresses the formation of SiO (silicon mono-oxide) resulting in lowering of the hot metal silicon content.
High pressure oxygen – It refers to the condition where oxygen is present at high pressures, which can lead to the synthesis of transition element-containing compounds with higher oxidation states and altered physical properties.
High-pressure piping – It involves designing, analyzing, and installing systems operating above standard pressure ratings (frequently exceeding 1 mega-pascal to safely transport high-pressure fluids and gases. It needs strict adherence to specialized codes, focusing on high-strength materials, rigorous stress analysis, and thorough testing to prevent catastrophic failures.
High-pressure pump – It is a device designed to increase the pressure of fluids (liquids or gases) by converting mechanical energy into hydraulic energy, typically generating operating pressures exceeding 17 mega-pascals or up to 140 plus mega-pascals in specialized applications. These robust, heavy-duty machines, including reciprocating plunger, piston, or high-speed centrifugal types, are necessary for applications needing high-force output, such as hydraulic fracturing, industrial cleaning, descaling, and fluid transport.
High-pressure ratio – It focuses on designing machinery, such as centrifugal compressors, gas turbines, and turboexpanders, to achieve discharge-to-inlet pressure ratios exceeding 25 to 30, with some applications reaching up to 40 mega-pascals. Driven by the need for improved efficiency, reduced footprint in energy-intensive, and green-hydrogen applications, this field leverages high-speed rotors, advanced aerodynamics, and specialized materials to handle substantial thermal and mechanical stress.
High-pressure spot – Localized area of insufficient resin, usually identified by low gloss, dry spots, or fiber showing on the surface.
High-pressure steam boiler – A high-pressure steam boiler is a steam boiler which operates at pressures above 103 kilo-pascals. These are also called power boilers.
High-pressure torsion – It is a severe plastic deformation (SPD) technique which refines material micro-structure to the nano-meter level by applying high compressive pressure (several giga-pascals) and concurrent shear deformation (torsion) to thin, disk-shaped samples. It dramatically increases strength and hardness by producing ultra-fine grains.
High-pressure turbine – It is the initial, high-temperature expansion stage in gas or steam turbines, responsible for extracting maximum energy from high-pressure fluid to drive the compressor (in engines) or generator (in power plants). It operates under extreme conditions, utilizing specialized materials and cooling, typically featuring impulse-reaction blading.
High-pressure water pumps – These are mechanical devices designed to significantly increase water pressure, frequently exceeding 7 mega-pascals, to move fluids over long distances, high elevations, or for specialized industrial cleaning and cutting applications. They are characterized by robust, multi-stage construction using positive displacement or centrifugal technology.
High product quality – It is defined as the measure of excellence where a product consistently meets or exceeds customer needs, specifications, and regulatory standards through superior design, reliability, and functionality. It involves ‘fitness for purpose’ and conformance to requirements, ensuring the product is durable, safe, and efficient.
High pulse repetition frequency – It involves designing systems which transmit a high number of pulses per second (frequently in kilo-hertz) to achieve high-velocity Doppler resolution and, in radar, to eliminate speed ambiguities. It is important for applications like fire-control radar, velocity measurement, and high-speed ultrasound imaging, though it causes range ambiguities.
High quality factor (Q-factor) – it optimizes resonant systems, mechanical, electrical, or optical, to minimize energy loss relative to stored energy, resulting in narrow bandwidths and high-precision, stable performance. Key techniques include minimizing material defects, optimizing geometry, and improving material purity to reduce dissipation, frequently utilized in resonators, sensors, and filters.
High-quality product – It is defined as an offering which consistently meets or exceeds customer requirements, stakeholder expectations, and regulatory standards through inherent, validated characteristics. It is achieved by implementing structured processes, including planning, control, assurance, and continuous improvement, which guarantee safety, usability, and reliability.
High-quality product engineering – It is a proactive, multi-disciplinary approach which embeds quality, reliability, and efficiency from conception through production, rather than just testing for defects at the end. It integrates advanced techniques like simulation, automation, and continuous improvement / continuous delivery or deployment (CI/CD) to reduce waste, optimize performance, and meet, or exceed, customer expectations.
High-range water reducer – It is also called superplasticizer. It is a chemical admixture for concrete which considerably reduces water content (typically 12 % to 30 % or more) without reducing workability, or increases slump / flow considerably without affecting water content. Used to produce high-strength or self-consolidating concrete (SCC), it disperses cement particles to improve, strength, density, and durability, frequently used in precast, prestressed, and high-rise applications.
High-rank coal – It is mature coal with high carbon content (86 % to 98 %), low moisture, and low volatile matter (2 % to 12 %). It possesses high thermal maturity, hardness, and calorific value, frequently used for specialized, low-smoke industrial applications.
High-rate anaerobic reactor – It is an engineered wastewater treatment system designed to maximize organic degradation by retaining high concentrations of active, granular, or immobilized biomass. These reactors uncouple solid retention time (SRT) from hydraulic retention time (HRT), allowing high organic loading rates (OLR) and short retention times while efficiently producing methane-rich biogas.
High-rate deformation – it refers to the rapid, frequently dynamic, shaping or loading of metallic materials, typically at strain rates exceeding 100 to 1,000 per second. It involves substantial adiabatic heat generation and, in several cases, leads to high-strength, high-hardness micro-structures. These conditions are normal in manufacturing processes like high-velocity impact, forging, or shock loading.
High-recovery valve – It is a valve design which dissipates relatively little flow stream-energy because of streamlined internal contours and minimal flow turbulence. Hence, pressure downstream of the valve vena contracta recovers to a high percentage of its inlet value. Straight-through flow valves, such as rotary ball valves, are typically high-recovery valves.
High residual phosphorus copper – It is the deoxidized copper with residual phosphorus present in quantities (normally 0.013 % to 0.04 %) normally sufficient to decrease appreciably the conductivity of the copper.
High resistance state – It is a stable, high-impedance state in a resistive switching device, such as a memristor or RRAM (resistive random-access memory) which allows very little current to flow, representing a logic ‘0’ or ‘off’ state. It is one of at least two, or sometimes multiple, non-volatile memory states, with higher electrical resistance compared to the ‘low resistance state’ (LRS).
High-resolution (HR) imagery – It refers to visual data with exceptional detail and clarity, typically defined in remote sensing as having a spatial resolution of 1 meter or better (30 centimeters to 50 centimeters for very high resolution). It uses high pixel / dot density (DPI) to enable precise analysis, feature extraction, and reduced ambiguity, necessary for applications like structural inspection, and disaster management.
High-resolution transmission electron microscopy – It is an imaging mode of specialized transmission electron microscopes that allows for direct imaging of the atomic structure of samples. It is a powerful tool to study properties of materials on the atomic scale, such as semi-conductors, metals, nano-particles and sp2-bonded carbon (e.g., graphene, carbon nano-tubes). This term is also frequently used to refer to high resolution scanning transmission electron microscopy, mostly in high angle annular dark field mode.
High Reynolds number (Re) – It defines a fluid regime where inertial forces dominate viscous forces, resulting in turbulent, chaotic flow, intense mixing, and frequently, high drag. It indicates that fluid viscosity is insufficient to dampen instabilities, leading to rapid, random velocity fluctuations. In case of high Reynold number, ‘Re’ value is above 4,000 for pipe flow, frequently higher for external flows.
High Reynolds number (Re) flow – It describes fluid motion dominated by inertial forces rather than viscous forces, leading to turbulent, chaotic behaviour with substantial mixing. Normally defined as ‘Re above 4,000’ in pipes, or very high ‘Re’ (e.g., I million to 10 million) in aerodynamics, it indicates thin boundary layers, high energy, and frequently dictates a need for empirical, rather than analytical, modeling.
High rolling mills – These are the rolling mills which are installed above the ground level, normally 5 meters to 6 meters above the ground level. This is done to facilitate the mill maintenance. Normally light section mills and wire rod mills are installed above the ground level. High in the rolling mill also indicates the number of rolls in a mill stand. Accordingly, a rolling mill can be 2-high, three- high, four-high, six-high or Z-high.
High scanning speed – It refers to the rapid movement of a laser beam or sensor across a target surface, normally exceeding 1 meter per second in additive manufacturing (e.g., selective laser melting / laser powder bed fusion) or high-frame-rate capture in 3D scanning. It enables faster data acquisition, higher cooling rates (up to 1.68 million K per second), reduced heat input, and increased production efficiency.
High salt concentration – It normally refers to solutions or environments with, or exceeding, twice the salt content of standard seawater (frequently grams per litre or parts per trillion), characterized by high electrical conductivity, increased density, and high osmotic pressure. These conditions are normal in industrial wastewater (high total dissolved solids), hypersaline environments, and advanced, concentrated electrolyte systems in batteries.
High-sensitivity analysis – It is a, typically computational, method which quantifies how small variations in input parameters (e.g., material properties, dimensions) disproportionately affect a system’s output performance, such as safety, stability, or cost. It identifies critical variables to optimize design robustness and reliability.
High shear rate – It is a fluid dynamics condition defined by a rapid change in velocity between adjacent fluid layers, normally occurring in narrow gaps, high-speed mixing, or pumping processes. It is quantified by a high velocity gradient (dv/dy), typically measured in ‘per second’, and causes substantial shear-thinning (reduced viscosity) in non-Newtonian fluids.
High-side switch – It is an electronic component which connects or disconnects a power supply from a load by being placed between the positive voltage source and the load. It sources current to the load, providing superior safety in ground-fault scenarios compared to low-side switches, and is normally used in automotive and industrial applications.
High-silicon cast iron – It is a specialized, highly corrosion-resistant, and brittle alloy containing 14 %–18% silicon (very frequently 14.5 % to 15 %), designed for handling aggressive acids. It forms a protective silica (SiO2) layer, resisting sulphuric and nitric acids, but is limited by low impact toughness, high porosity, and poor machinability.
High-solids paint – It is the paint containing 35 % to 80 % solids. These products have become popular because of the reduction in solvent emissions associated with their use.
High spatial frequency – It refers to rapid, abrupt, or fine-grained changes in signal intensity, pixel values, or structural patterns across a given distance. It represents fine details, sharp edges, and high-resolution information, typically measured in cycles per unit distance (e.g., lines per millimeter). High-spatial-frequency components are necessary for sharp image resolution, whereas low-frequency components represent overall shape. It is important is crucial for applications requiring high-precision detail, such as in microscopy, magnetic resonance imaging, and computer vision.
High spatial frequency laser-induced periodic surface structures – These refer to a specific type of self-organized sub-wavelength surface nano-structure created on materials (such as metals, semiconductors, and dielectrics) when irradiated with specialized, typically ultrashort, laser pulses. These are ripple-like structures with a spatial period (L) considerably smaller than the wavelength of the laser (l), frequently falling in the range of ‘L is less than l/2 or even ‘L is less than l/10.
High spatial resolution imaging – It refers to systems capable of resolving fine, detailed, or small features, characterized by a small ‘ground sample distance’ (GSD), frequently sub-meter in remote sensing. It indicates a high number of pixels per unit area, allowing for precise distinction of close-together objects, rather than just high pixel count.
High spectral efficiency -It is the ability of a communication system to transmit a maximum quantity of data (bits per second) over a given radio frequency bandwidth (Hertz). It is measured in bits per second per hertz and indicates how effectively a modulation scheme utilizes limited, valuable spectrum.
High spectral resolution – It refers to an instrument’s ability to distinguish, resolve, and measure very narrow, closely spaced wavelength bands within the electro-magnetic spectrum. Characterized by high-density sampling and small bandwidths (frequently nano-meter-scale or less), it provides precise, detailed spectral data, enabling the identification of specific materials or chemical components.
High speed – It is a relative term which defines operational parameters considerably above ‘conventional’ or ‘normal’ standards. It is normally characterized by increased power density, higher material stresses, reduced operating times, and specific, frequently application-dependent, thresholds.
High-speed and hard machining – It consists of high-productivity machining processes which achieve cutting speeds in excess of 600 metres per minute and up to 18,000 metres per minute. It is a, frequently 5 times to 10 times faster than conventional, production-focused process optimizing material removal rates, speed, and feed to reduce cutting forces and heat. Hard machining focuses on cutting materials with hardness e.g., 45 HRC (Rockwell hardness scale C) to 68 HRC, directly with cutting tools, frequently replacing grinding for high-precision components.
High-speed circuit – it is an electronic system where signal integrity is compromised by parasitic effects, needing transmission line design principles. It is normally defined by fast edge rates (rise / fall times) rather than just high frequency, specifically when the signal propagation delay exceeds 1/2 or 1/6 of the rise time.
High-speed circuitry – It refers to electronic circuits where signal integrity is compromised by parasitic effects, needing specialized design techniques (like controlled impedance) since the signal rise time is comparable to or faster than the propagation delay. It is normally defined by fast edge rates (below 1 nano-second rather than high clock frequencies alone.
High speed diesel oil – It is a complex mixture of hydro carbons. It is a brown-coloured oily liquid with pungent smell. It has a pungent smell. Its vapour density is 3 to 5 (air=1). It is insoluble in water. Its specific gravity is in the range of 0.81 to 0.91 (water=1). It is a neutral liquid (neither acidic nor basic). High speed diesel is flammable with a flash point ranging from 32 deg C to 96 deg C. Its auto ignition temperature is 256.6 deg C. It is used in diesel engines of mobile equipment, automobiles, diesel-generator sets, and locomotives. It is the prime mover in a wide range of power generation and pumping applications. The diesel engines are normally of high compression and self-ignition engines. Fuel is ignited by the heat of high compression. High speed diesel oil is normally used as a fuel in medium-speed and high-speed compression ignition engines (operating above 750 rpm).
High-speed die sinking – It is also known as ‘electrical discharge machining (EDM). It is a non-traditional, electro-thermal manufacturing process used to rapidly create precise, complex 3D cavities, blind holes, or intricate features in electrically conductive materials. It operates by submerged, controlled spark erosion where a shaped electrode (normally copper or graphite) acts as a ‘3D stamps’ to remove material through melting and vapourization at temperatures reaching 8,000 deg C to 12,000 deg C.
High-speed gear wheel – It is a specialized, precision-engineered mechanical component designed for power transmission in systems operating at high rotational speeds (e.g., 8,000 revolutions per minute to 20,000 plus + revolutions per minute or 140 meters per second to 180 meters per second tip speeds in turbo-compressors). Metallurgically, these gears need high strength, superior fatigue resistance, low distortion, and exceptional surface finish to minimize noise and prevent wear.
High-speed machining – It consists of high-productivity machining processes which achieve cutting speeds in excess of 600 metres per minute and up to 18,000 metres per minute. It is a, frequently 5 times to 10 times faster than conventional, production-focused process optimizing material removal rates, speed, and feed to reduce cutting forces and heat.
High-speed milling – It is a specialized metal-cutting process characterized by exceptionally high spindle speeds (15,000 to higher than 40,000 revolutions per minute) and high feed rates, normally 5 times to 10 times faster than conventional milling. It is used to remove material quickly while maintaining high accuracy and surface finish. It utilizes advanced tool materials (carbide, diamond, ceramics) to withstand high temperatures.
High-speed pump – It is a centrifugal or dynamic pump designed to operate at high rotational speeds, frequently 3,000 revolutions per minute (rpm) to over 10,000 plus rpm, to achieve high head pressure in a compact size. These pumps frequently use speed-increasing gear-boxes or special high-speed couplings, featuring single or multi-stage impellers, and are normally used for high-pressure, low-flow, or condensate applications.
High-speed steel – It is a highly alloyed tool steel designed to maintain exceptional hardness, above HRC 60 (Rockwell hardness scale C) and red hardness at temperatures up to 600 deg C. It is characterized by high carbon (higher than 0.6 %) and, typically, higher than 7 % total alloying elements like tungsten, molybdenum, chromium, vanadium, and cobalt. These additions improve wear resistance and cutting efficiency.
High speed tool steels – Steels which are alloyed in such a way that they can be used as a cutting tool material to machine other metals at high speeds, and still retain its cutting ability, even though the tool tip is at a low red heat. The different grades of these steels contain 0.6 % or more of carbon, a combined content of 7 % or more of the elements like tungsten, molybdenum, and vanadium, 3 % to 6 % of chromium and in those needed to operate at the highest temperatures additions of 4 % to 13 % of cobalt. These steels are widely used for the production of taps, dies, twist drills, reamers, saw blades and other cutting tools. These steels form a special class of highly alloyed tool steels, combining properties such as high hot hardness and high wear resistance. These are so named mainly because of their ability to machine materials at high cutting speeds.
High-speed water jet – It is an industrial, non-traditional machining technology which uses a highly pressurized, focused stream of water, frequently mixed with abrasives, to cut, pierce, or clean materials by eroding them with extreme kinetic energy. Operating at pressures up to 620 mega-pascal, it acts as a cold-cutting method with no heat-affected zones.
High stacking fault energy – It refers to materials (typically metals) with a high energy penalty (above 50 mega-joules per square meter to 100 mega-joules per square meter) for disrupting the normal stacking sequence of atomic planes, such as ABCABC in fcc (face-centred cubic) crystals. This high energy prevents dislocation dissociation into wide partials, promoting easy cross-slip, wavy glide, and higher ductility over deformation twinning.
High-stacking-fault-energy materials – These are metallic alloys or pure metals (typically with a face-centered cubic structure) which need a relatively high quantity of energy to create a fault in their stacking sequence of atomic planes. Because of this high energy need, dislocations in these materials do not dissociate widely into partial dislocations, rather, they remain as full (perfect) dislocations, which facilitates specific deformation mechanisms like cross-slip and climb, resulting in characteristic mechanical behaviours.
High-stacking-fault-energy metals – These are metals where the energy needed to create stacking faults in the crystal lattice is high, resulting in narrow dissociation distances between partial dislocations. These metals, such as aluminum or copper, prefer deformation by slip, cross-slip, and climb, allowing for high ductility and reduced twin formation.
High strain concentration – It refers to a localized region in a material where the deformation (strain) is considerably higher than the average (nominal) strain of the surrounding material. It is a phenomenon caused by geometric irregularities, such as holes, notches, fillets, or sharp corners, which interrupt the smooth flow of stress through a component, leading to severe, localized deformation.
High strain hardening – It is also called work hardening. It is the process where a material, typically metal, increases in strength and hardness because of the plastic deformation below its recrystallization temperature. This occurs since dislocation density increases, causing them to interfere with each other and needing higher stress for further deformation.
High strain rate – It refers to the condition in which materials are subjected to rapid deformation, typically characterized by strain rates upwards of 100 per second as seen in high strain rate tensile testing relevant to impact events, such as automotive crashes. This condition is important for evaluating material performance in safety-critical applications where impact resistance is a major concern.
High-strain-rate processing – It refers to the rapid deformation of metals, typically at rates exceeding 100 to 1,000 per second. This technique, used in impact, explosion, or high-speed machining, induces substantial microstructural changes, such as high dislocation density, grain refinement, and adiabatic heating, which increase material strength.
High strain rate super-plasticity – It is a phenomenon where metallic alloys show exceptionally high tensile ductility, frequently exceeding 400 % elongation, at strain rates of higher than or equal to 0.01 per second. Mainly achieved in ultrafine-grained materials (below I micro-meter) through severe plastic deformation, high strain rate super-plasticity reduces forming times for complex industrial components, improving manufacturing efficiency.
High strength alloys – These are materials designed to achieve high levels of strength and toughness, often by tailoring their micro-structure to improve properties such as corrosion resistance and performance under different conditions. These alloys include specific compositions which allow for superior mechanical characteristics compared to conventional materials.
High-strength aluminum alloys – These are heat-treatable, high-performance materials, mainly aluminum-copper and aluminum-series, designed for superior strength-to-weight ratios, frequently exceeding 690 mega-pascals in tensile strength. Metallurgically, they achieve high strength through precipitation hardening (age hardening), refining grain structure, and alloying with copper, zinc, magnesium, and silicon, making them important for aerospace and automotive applications.
High strength bolts – These bolts are made from high-strength carbon steel or from tempered alloy steel. The high-strength materials tend to increase the bolt strength roughly by 25 % to 50 %.
High strength cast steels – These steels cover the tensile strength range of 1,200 MPa to 2,060 MPa. Cast steels with these strength levels and with considerable toughness and weldability were originally developed for military applications. These cast steels can be produced from any of the above medium alloy compositions by heat treating with liquid quenching techniques and low tempering temperatures.
High strength concrete – It is the concrete with compression strengths with more than 425 kilograms per square millimeters are referred to as high-strength concretes. This concrete is also sometimes called high-performance concrete since it has other excellent characteristics besides just high strength. For example, the low permeability of such concrete causes it to be quite durable as regards the various physical and chemical agents acting on it which can cause the material to deteriorate. High-strength concretes are sometimes used for both precast and pre-stressed members. They are particularly useful in the precast industry where their strength enables the production of smaller and lighter members, with consequent savings in storage, handling, shipping, and erection costs. In addition, they have sometimes been used for offshore structures, but their common use has been for columns of tall reinforced concrete buildings, where the column loads are very large.
High-strength controlled-expansion superalloys – These are a specialized class of nickel-iron-cobalt (Ni-Fe-Co) alloys engineered to possess both high-temperature creep strength (retaining structural integrity at elevated temperatures) and a low, stable coefficient of thermal expansion (CTE). They are designed to maintain tight clearances between rotating and stationary components (e.g., turbine blades and casings) in aircraft gas turbines, reducing efficiency-robbing air leakage.
High-strength low-alloy (HSLA) steels – These steels are designed to provide better mechanical properties and / or higher resistance to atmospheric corrosion than conventional carbon steels. They are not considered to be alloy steels in the normal sense since they are designed to meet specific mechanical properties rather than a chemical composition (High strength low alloy steels have yield strengths higher than 275 MPa). The chemical composition of a specific high strength low alloy steel can vary for different product thicknesses to meet mechanical property requirements. The high strength low alloy steels have low carbon contents (0.05 % to 0.25 %) in order to produce adequate formability and weldability, and they have manganese contents up to 2 %. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium are used in different combinations.
High-strength materials – These are alloys (e.g., maraging steel, titanium) engineered for superior resistance to deformation, fracture, and yielding under load. Defined by high yield strength (higher than 1,378 mega-pascals) and ultimate tensile strength (higher than 1,550 mega-pascals), these materials optimize performance through tailored micro-structures, frequently prioritizing a high strength-to-weight ratio for structural applications.
High strength steels – These are carbon low alloy steels which have yield strength higher than 275 mega-pascals and can be classified normally in four types namely (i) as-rolled carbon-manganese steels, (ii) as rolled high strength low alloy steels also known as micro-alloyed steels, (iii) heat treated (normalized or quenched and tempered) carbon steels, and (iv) heat treated low alloy steels. These four types of steels have higher yield strengths than mild carbon steel in the as hot rolled condition. The heat-treated low alloy steels and the as rolled high strength low alloy steels also provide lower ductile-to-brittle transition temperatures than do carbon steels.
High-strength structural steel – It is a low-alloy material with a minimum yield strength typically exceeding 60 mega-pascals, offering superior strength-to-weight ratios compared to conventional carbon steel. Designed for high-stress applications (bridges, crane booms, buildings), it combines high tensile strength with good weldability, toughness, and ductility.
High-strength-to-density ratio steels – These are also called high-specific-strength steels. These are ferrous alloys engineered to provide exceptional yield strength (above 460 mega-pascals), frequently exceeding 1,000 mega-pascals) while maintaining a relatively low, consistent density (around 7.75 to 8.05 grams per cubic meter. These materials, such as AHSS (advanced high-strength Steels) and HSLA (high-strength low-alloy) steels, maximize structural performance, allowing for substantial weight reduction, improved fuel efficiency, and improved payload capacity without sacrificing structural integrity.
High-stress abrasion – It is a form of abrasion in which relatively large cutting forces are imposed on the particles or protuberances causing the abrasion, and which produces considerable cutting and deformation of the wearing surface. In metals, high-stress abrasion can result in considerable surface strain hardening. This form of abrasion is common in mining and agricultural equipment, and in highly loaded bearings where hard particles are trapped between mating surfaces.
High-stress behaviour – It refers to the mechanical response of a material when subjected to substantial external forces, loads, or pressures which approach or exceed its yield strength, resulting in substantial deformation or failure. This behaviour is characterized by the transition from reversible elastic deformation to irreversible plastic deformation, where the material undergoes permanent changes in shape.
High-stress grinding abrasion – It is a wear mechanism which occurs when abrasive particles are trapped between two surfaces (three-body) or forced against a single surface (two-body) under high loads, causing the abrasive particles themselves to break or crush during the wear process.
High stretch rate – It refers to the rapid deformation of materials, typically exceeding 100 per second to 1000 per second. It measures the speed at which a material’s elongation occurs relative to its original length over time, frequently resulting in increased stress and higher tensile strength.
High sulphate nickel plating solution – It is a type of acidic electrolytic bath designed for electro-depositing nickel, characterized by a high concentration of nickel sulphate (NiSO4) as the main nickel ion source. These solutions are used for producing bright, hard, and wear-resistant coatings, frequently applied where moderate thickness and high aesthetic quality are needed.
High surface area – It defines materials with a massive, exposed surface relative to their small volume or mass, typically achieved through porous structures or nano-technology. This characteristic dramatically increases active sites, improving efficiency in catalysis, filtration, adsorption, and energy storage by boosting interaction with the surrounding environment.
High technology – It is also known as advanced technology. It is the technology which is at the cutting edge, i.e., the highest form of technology available. It can be defined as either the most complex or the newest technology on the market. The opposite of high tech is low technology, referring to simple, frequently traditional or mechanical technology. When high technology gets old, it becomes low technology, for example vacuum tube electronics.
High-temperature adhesives – These are specialized materials formulated to maintain structural bond strength, chemical stability, and sealing capabilities at high temperatures, typically exceeding 150 deg C to 300 deg C, and up to 1,650 deg C for ceramic types. Unlike standard adhesives, they resist degradation, thermal cycling, and oxidation in demanding industrial environments.
High-temperature alloys – These are also called superalloys. These are specialized metal materials, typically based on iron, nickel, or cobalt, engineered to maintain high mechanical strength, creep resistance, and oxidation resistance at temperatures exceeding 600 deg C. They are important for aerospace, gas turbines, and chemical processing. These alloys are designed to withstand structural stress and environmental degradation (oxidation / corrosion) at high temperatures where conventional metals fail.
High-temperature applications – These applications involve systems, materials, and processes designed to operate reliably at high temperatures, normally defined as exceeding 500 deg C (or above 100 deg C to 125 deg C for electronics), where standard materials fail because of oxidation, creep, or loss of strength. These applications focus on material stability, durability, and performance under extreme thermal conditions, utilizing specialized materials like superalloys and ceramics.
High-temperature catalyst – It is a substance designed to increase chemical reaction rates while operating effectively and maintaining structural integrity at high temperatures, typically exceeding 300 deg C to 400 deg C. These catalysts, frequently metal oxides or noble metals, resist sintering and degradation, enabling stable, efficient operation in harsh industrial processes like syngas production, hydrocarbon oxidation, and catalytic combustion.
High-temperature coatings for superalloys – These are specialized surface engineering treatments applied to nickel-based, cobalt-based, or iron-based alloys to protect them from aggressive environmental degradation (specifically oxidation, hot corrosion, and erosion) at temperatures often exceeding 900 deg C to 1,100 deg C. These coatings allow gas turbine components (blades, vanes) to operate efficiently at temperatures which otherwise cause the underlying alloy to soften, creep, or melt. Metallurgically, these coatings function by creating a stable, adherent, and slow-growing oxide scale (normally Al2O3 or Cr2O3) which acts as a barrier, with the coating itself acting as a reservoir of active elements (aluminum, chromium, and silicon) to heal the scale during service.
High-temperature collectors – These are solar thermal collectors which operate at temperatures exceeding 300 deg C, mainly utilized in high-temperature industrial applications and solar thermal power plants.
High-temperature combustion – It is an analytical technique for determining the concentrations of carbon and sulphur in samples. The sample is burned in a graphite crucible in the presence of oxygen, which causes carbon and sulphur to leave the sample as carbon di-oxide and sulphur di-oxide. These gases are then detected by infrared or thermal conductive means.
High temperature corrosion – It is the corrosion by gases or deposits or both gases and deposits occurring at high temperatures under conditions where aqueous electrolytes no longer exist. It is to be noted that the high temperature corrosion can become significant at temperatures above 170 deg C depending on material and environment.
High-temperature effects – These refer to the degradation of material properties, such as reduced strength, increased ductility, creep, and thermal fatigue, because of high operational temperatures. These thermal effects also accelerate chemical reactions like oxidation and corrosion, causing structural deformation and potential failure.
High-temperature electrolysis – It is also called steam electrolysis. It is an engineering process which splits water into hydrogen (H2) and oxygen (O2) using electrical energy and high-grade thermal energy (700 deg C to 1,000 deg C), typically using solid oxide electrolysis cells (SOECs). It offers higher efficiency than low-temperature methods by reducing electricity consumption through thermal input, achieving 700 deg C to 1,000 deg C in industrial applications.
High-temperature engineering – It involves designing materials, systems, and processes to operate reliably in environments exceeding standard, normally over 800 deg C for processes or above 125 deg C for electronics, where materials approach melting points or face severe degradation. It focuses on managing creep, thermal expansion, oxidation, and structural integrity in specialized applications like turbine blades, nuclear reactors, and high-energy devices.
High-temperature erosion – It is the process of material degradation because of the mechanical interaction of solid particles or fluids at high temperatures, frequently in industrial settings. It is a significant wear mechanism in several applications like gas turbines, furnaces, incinerators, and power plants, where high temperatures and process gases can lead to accelerated material loss. This erosion is frequently coupled with oxidation, making the wear process more complex. The erosive force can come from solid particles (e.g., fly ash, slag, and sand) or high-velocity fluids. High temperatures affect considerably the material’s mechanical properties, making it more susceptible to erosion.
High-temperature fatigue – It is the degradation and failure of engineering materials under cyclic mechanical loads or temperature variations (thermal fatigue) at high temperatures (typically above 0.5 Tm, the melting point). It combines fatigue damage with time-dependent creep and environmental damage, reducing fatigue life through accelerated crack initiation and propagation.
High-temperature Fischer-Tropsch – It is a process converting syngas (carbon mono-oxide + hydrogen) into synthetic fuels, operating at 300 deg C to 350 deg C (around 100 deg higher than low temperature Fischer-Tropsch) and pressures typically around 1 mega-pascal to 3 mega-pascal, using iron-based catalysts in fluidized bed reactors. It is designed for maximum gasoline and light olefin production, characterized by the absence of a liquid phase surrounding the catalyst particles.
High-temperature flow – High temperatures because of a manifestation of viscous dissipation cause non-equilibrium chemical flow properties such as vibrational excitation and dissociation and ionization of molecules resulting in convective and radiative heat-flux.
High-temperature gas cleaning – It is a process which removes contaminants, particulates, tars, and gases (hydrogen sulphide, H2S, hydrochloric acid, HCl, alkali compounds), from industrial or synthesis gases at temperatures typically exceeding 250 deg C. It increases thermal efficiency by eliminating the need to cool gases before downstream usage, such as in turbines or solid oxide fuel cells (SOFCs).
High-temperature gas-cooled reactors – These are ‘generation IV ‘nuclear fission reactors which use helium as a coolant, graphite as a moderator, and ceramic-coated fuel particles (TRi-structural ISOtropic particle fuel) to produce high-temperature heat (700 deg C to 1,000 deg C plus). Designed for high efficiency, they provide process heat for industrial applications and electricity generation. These reactors enable high electric efficiency over 50 % and are mainly designed for hydrogen production and industrial process heat applications.
High temperature gradient – It is a, typically, undesirable condition where temperature changes rapidly over a very short distance, causing a significant, non-uniform, and steep thermal imbalance (e.g., above 30 deg C per centimeter). It represents a high rate of heat flow, leading to intense thermal stress, cracking, or delamination in materials.
High-temperature heat exchanger – It is a device designed to transfer thermal energy between fluids (liquid or gas) at temperatures normally exceeding 500 deg C to 600 deg C. These systems, frequently utilized in power generation, and chemical processing, need specialized materials to resist creep, oxidation, and corrosion.
High-temperature heat recovery – It is the process of capturing and reusing thermal energy from industrial waste streams, typically exhaust gases or products, operating at temperatures above 650 deg C. It maximizes energy efficiency by recovering high-grade heat from furnaces, kilns, and reactors to preheat combustion air or raw materials, considerably reducing main fuel consumption.
High-temperature hydrogenation – It consists of non-catalytic hydrogenation which takes place only at very high temperatures. Among different hydrogenation methods, high-temperature hydrogenation is a critical approach with specific applications. By subjecting materials to high temperatures in a hydrogen-rich environment, this treatment method can induce chemical reactions and micro-structure changes, tuning materials’ mechanical performance.
High-temperature hydrogen attack – It is a loss of strength and ductility of steel by high-temperature reaction of absorbed hydrogen with carbides in the steel resulting in decarburization and internal fissuring.
High-temperature lubricants – These are specialized substances designed to reduce friction, wear, and heat between moving surfaces at high temperatures, typically exceeding 350 deg C, where conventional liquid lubricants fail because of the decomposition or oxidation. These lubricants, frequently comprising synthetic base oils, complex thickeners, or solid materials like graphite, molybdenum di-sulphide, and metal oxides, maintain stability and provide necessary lubrication in extreme, heavy-load environments.
High-temperature lubrication – It refers to specialized lubrication systems, mainly solid lubricants, specialized greases, or coatings, designed to minimize friction and wear on mechanical components operating in extreme thermal environments, normally exceeding 350 deg C. These materials are necessary when conventional liquid lubricants (oils / greases) fail because of the rapid thermal degradation, oxidation, or evaporation, frequently used in industrial kiln applications.
High-temperature operations – These involve systems, materials, or processes functioning at high temperatures, frequently exceeding 800 deg C for reactors or 125 deg C for electronics, typically exceeding the normal operating range. These conditions need specialized materials to resist creep, oxidation, and, frequently, a Top/Tmelt ratio exceeding 0.6.
High-temperature phases – These define the structural, chemical, or physical state of materials, where properties deviate from ambient behaviour, needing. High temperature phase refers to chromatographic stationary phases which are stable at high temperatures, typically up to 500 deg C, allowing for reduced stationary phase bleed and enhanced performance with sensitive detection methods. These phases frequently utilize materials such as substituted silicone–carborane copolymers, which can withstand temperatures as high as 450 deg C.
High-temperature reactors – These are ‘Generation IV’ nuclear fission reactors which use graphite moderation and helium coolant to operate at outlet temperatures of 700 deg C to over 1,000 deg C. Engineered for high thermal efficiency and safety, they utilize coated particle fuel (TRi-structural ISOtropic particle fuel) to provide passive decay heat removal and facilitate high-temperature process heat for industrial applications.
High-temperature recovery – It refers to capturing and reusing waste heat from industrial processes, typically occurring at temperatures above 650 deg C to 750 deg C , such as from furnaces, kilns, or molten slag. It is a highly efficient method to reduce energy consumption, boost overall process efficiency, and preheat combustion air or water.
High temperature shift catalyst – It is an industrial catalyst, typically iron oxide (Fe3O4) promoted with chromium oxide (Cr2O3), designed to facilitate the water-gas shift reversible reaction (CO + H2 = CO2 + H2) at 310 deg C to 460 deg C. It maximizes hydrogen production, operates in sulphur-rich environments, and uses stabilizers to prevent sintering.
High-temperature shift reactor – It is an industrial unit designed to convert carbon mono-oxide (CO) and water vapour (H2O) into carbon di-oxide (CO2) and hydrogen (H2) through the exothermic water-gas shift reaction ((CO + H2 = CO2 + H2). Operating at 315 deg C to 430 deg C using iron-chromium catalysts, it maximizes conversion efficiency, to quickly reduce carbon mono-oxide concentration to roughly 2 % to 3 %, followed by cooling for further refinement in a low-temperature shift reactor.
High-temperature sintering – It is a thermal process which fuses compacted metal powders into a solid, high-density, and precise component by heating them to temperatures below their melting point, typically above 1,120 deg C. This technique improves atomic diffusion across particle interfaces, creating strong sinter necks, reducing porosity, and increasing the strength, conductivity, and density of the material.
High-temperature solar collectors – These are systems designed to concentrate solar radiation, using mirrors or lenses, to achieve operational fluid temperatures typically exceeding 300 deg C. They mainly power industrial processes and electric power production (concentrated solar power, CSP), frequently utilizing parabolic troughs or dishes to achieve high thermal efficiency.
High temperature steam electrolysis – It is a method for hydrogen production which utilizes thermal energy from nuclear reactors to split water at high temperatures (800 deg C to 1,000 deg C), hence consuming less electricity than conventional water electrolysis. This process involves converting water to steam and then dissociating it to form hydrogen molecules and oxygen ions. It uses solid oxide electrolyzer cells (SOEC), reducing electricity demand compared to liquid water electrolysis.
High-temperature superconductivity – It refers to the phenomenon of superconductivity occurring at temperatures above 30 K, with notable examples including materials like (LaBa)2CuO4 and YBa2Cu3O7, which show transition temperatures of 35 K and 90 K, respectively.
High-temperature superconductors – These are materials which show zero electrical resistance and the Meissner effect (expulsion of magnetic fields) at temperatures above 77 K (−196 deg C). This threshold allows them to be cooled by inexpensive liquid nitrogen rather than liquid helium, making them practical for applications like power cables, high-field magnets, and fault-current limiters.
High-temperature systems – These systems operate under extreme thermal conditions, typically above 125 deg C for electronics or over 150 deg C for heavy industrial processes, needing specialized materials, thermal management, and stress analysis. It involves designing components to withstand creep, thermal expansion, oxidation, and reduced material strength at elevated temperatures.
High-temperature tensile testing – It is a mechanical evaluation method performed above 35 deg C (frequently up to extreme temperatures) to determine the strength and ductility of metals under combined heat and tensile loading. By pulling heated samples until fracture, it measures critical properties like yield strength, ultimate tensile strength, and ductility, necessary for ensuring components (e.g., turbine blades) withstand harsh, high-heat environments.
High-temperature testing – It is the process of evaluating materials, components, or systems at high temperatures to ensure they maintain structural integrity, functional performance, and reliability under intended extreme operational environments. It measures properties like thermal stability, tensile strength, creep resistance, and, frequently, oxidation resistance.
High-temperature test reactor – It is a 30 MWth, graphite-moderated, helium-cooled research reactor in Japan designed by the JAEA (Japan Atomic Energy Agency) to demonstrate nuclear heat applications, such as hydrogen production, at temperatures up to 950 deg C. It is a necessary tool for testing fuel, materials, and passive safety systems for high-temperature gas-cooled reactors (HTGR).
High-temperature thermo-mechanical processing – It is a metallurgical technique combining plastic deformation (rolling, forging, extrusion) with heat treatment at temperatures above the material’s recrystallization point, frequently above 0.4 Tm (melting point). It simultaneously manipulates micro-structure and shape to improve mechanical properties, such as strength and toughness, through grain refinement.
High-temperature Winkler process – It is an advanced, pressurized, bubbling fluidized-bed gasification technology designed to convert solid fuels (lignite, coal, biomass, municipal solid waste) into high-quality synthesis gas (carbon mono-oxide + hydrogen). It operates at high temperatures (800 deg C to 1,000 deg C and pressures (up to 3 mega-pascals) to improve carbon conversion efficiency, minimize tar formation, and maximize throughput.
High tensile brasses – These brasses represent an important group of brasses whose strength has been increased by modifications to their chemical composition by additions of iron, nickel, manganese and / or aluminum. Aluminum or tin additions also improve corrosion resistance, Silicon additions are beneficial to wear properties.
High-tensile steel – High-tensile steels are low-carbon, or steels at the lower end of the medium-carbon range, which have additional alloying elements in order to increase their strength, wear properties or specifically tensile strength. These alloying elements include, chromium, molybdenum, silicon, manganese, nickel, and vanadium. Impurities such as phosphorus and sulphur have their maximum allowable content restricted.
High tensile stress – It refers to a high magnitude of internal resistance a material develops (force per unit area, S = F/A) when subjected to external pulling or stretching forces along its longitudinal axis. It represents the maximum tensile load a material can withstand before permanent deformation or breaking.
High thermal conductivity – It is a material property defining a high rate of heat transfer per unit area, per unit thickness, driven by a temperature gradient (k is measured in W/m.K). Materials with high thermal conductivity (e.g., metals like copper, aluminum) are necessary for efficient heat dissipation, thermal management, and preventing overheating in systems like heat exchangers, electronic packaging, and engine components
High thermal conductivity carbon block – It is made of high thermal conductivity materials and partial graphite materials. Pitch acts as binder. Main processes are extruding, baking, and processing. The product is with higher thermal conductivity. High thermal conductivity carbon block is used for the bottom of blast furnace.
High thrust – It refers to a high-magnitude propulsive force, typically generated by rotating machinery, which accelerates a large mass of gas at high velocity, as defined by Newton’s third law. It indicates a dominant force used to overcome gravity or high aerodynamic drag, often characterized by high mass flow rates.
High vacuum – It is a regime typically defined as an absolute pressure range between 0.1 pascals to 0.00001 pascals. In this range, the mean free path of gas molecules is comparable to or larger than the vacuum chamber dimensions, marking the transition to molecular flow.
High-value asset – It refers to information, systems, or physical equipment so critical that its loss, corruption, or compromise would severely impact an organization’s operations, safety, or mission. These are strategic assets requiring improved security and rigorous management throughout their lifecycle.
High-value product – It is an item, service, or commodity which offers substantial, frequently unique, benefits, such as superior quality, innovation, or specialized functionality, justifying a price premium and delivering higher profit margins compared to generic or commodity alternatives. These products frequently address specific needs of the customers, or operational efficiency.
High vapour pressure – It refers to a liquid’s high volatility and strong tendency to evaporate at a given temperature, creating high pressure in a closed container. These liquids (e.g., gasoline) easily convert to vapour, posing safety, storage, and cavitation risks in pumps and pipelines because of low boiling points.
High-velocity forging – It is also known as ‘high energy rate forging’ (HERF). It is a metal-working process which shapes materials by subjecting them to extremely high-impact velocities (frequently thirty hundreds of meters per second or higher) within milliseconds. Using explosive, hydraulic, or pneumatic energy to accelerate a ram, this method achieves complex, precise, and thin-part fabrication in a single stroke, considerably reducing cooling time and increasing strength in difficult-to-forge alloys.
High-velocity forming – High-velocity forming methods include techniques such as explosive forming and electro-magnetic forming. These techniques are distinct from most other metal forming methods in that the explosive or electro-magnetic force first accelerates the work-piece to a high velocity, and the kinetic energy of the work-piece is considerable. The sheet metal work-piece then changes shape, either as it strikes a die or as it is decelerated by plastic deformation. High-velocity forming is characterized by first imparting a high velocity to a work-piece, and this energy is turned to plastic deformation by constraint of the part or impact with a die. The velocity distribution for the part is determined by the pressure distribution or developed from the explosive, electro-magnetic pressure distribution (determined by coil shape) or shock wave profile. Changing the quantity of energy available changes the absolute values of the velocities. Once the velocity is imparted, the shape can be developed either by free forming or die forming.
High velocity impact – It refers to collisions occurring at speeds typically higher than 100 meters per second to 500 meters per second (frequently cited above around 10 to 11 meters per second for composite materials), where inertial forces dominate, causing localized damage like penetration, scabbing, or cratering. Unlike low-velocity impacts, these events frequently involve wave propagation effects, resulting in deformation, material fragmentation, or phase changes, such as melting or vapourization.
High-velocity metal forming – It consists of those processes in which high-strain-rate impulsive loading is used to deform sheet metal into the shape of a die into which it is accelerated. The advantages of high-velocity metal forming (HVMF) relative to conventional sheet-forming processes include improved formability and reduced wrinkling, more uniform strain distribution in a single forming step, reduced spring-back, and the ability to impart fine details over large areas. Including techniques such as explosive, electro-magnetic, and electro-hydraulic forming, these methods have been used for some time, mainly for very specialized applications with small lot sizes.
High-velocity oxygen fuel – It is a high velocity thermal spraying process which produces coatings with excellent adhesion and wear resistance. It is a thermal spraying coating method in which a mixture of oxygen and fuel is injected into the combustion chamber and subsequently ignited. The gas released in the combustion chamber is expelled at high velocities through a nozzle at very high pressures and temperatures. This thermal spray coating process is used to improve or restore a component’s surface properties or dimensions, hence extending equipment life by significantly increasing erosion and wear resistance, and corrosion protection.
High-velocity oxygen fuel spraying – It is a thermal spray process which burns fuel (kerosene, hydrogen, propane) and oxygen to create a high-pressure, supersonic gas stream. Powdered materials are injected, heated, and accelerated to extremely high velocities (around 800 meters per second to 1,000 meters per second, creating dense, low-porosity (less than 1 % to 2 %) coatings with superior adhesion, hardness, and wear / corrosion resistance.
High-velocity region – It refers to a specific zone within a system, such as fluid flow, aerodynamic fields, or material impact zones, where particle, gas, or projectile velocity considerably exceeds average flow or, in impact, where kinetic energy causes rapid, localized damage like melting or deformation.
High volatile bituminous coal – It is a ranked fuel defined by having above 31 % volatile matter (dry, ash-free) and below 69 % fixed carbon, normally containing high porosity and significant moisture. It is categorized (A, B, C) by calorific value (5850 kilo-calories per kilogram to 7,800 kilo-calories per kilogram) and represents a mid-rank fuel frequently used for combustion.
High voltage – It is the voltage at which safety concerns apply. In some contexts, anything over 100 volts can be a high voltage. In electric power transmission, voltages over 66,000 volts are considered high voltage.
High voltage alternating current – Depending on context, it can be hundreds or hundreds of thousands of volts.
High-voltage cable – It is a flexible insulated electrical conductor designed to withstand a considerable voltage. ‘High’ voltage can be hundreds or hundreds of thousands of volts, depending on the context.
High-voltage direct current – It is a technology which converts high-voltage alternating current (AC) to direct current (DC) for efficient long-distance, bulk power transmission or inter-connection of asynchronous alternating current grids. It offers lower losses than alternating current over long distances, using converter stations, ‘line-commutated converter’ (LCC) or ‘voltage source converter (VSC), to transmit power through overhead lines or underground / submarine cables. It is a system for power transmission which uses high direct current voltages for reasons of economy or stability.
High voltage direct current converter station – It is an element of a high-voltage direct current power transmission system. Each end of the transmission line has a converter station connected to the local alternating current grid.
High voltage direct current lines – These lines are part of high voltage direct current transmission systems which facilitate the transfer of electrical energy over long distances, enabling the inter-connection of asynchronous power systems and reducing stability issues associated with traditional alternating current (AC) transmission.
High-voltage direct current systems – These are specialized electrical engineering technologies which convert alternating current (AC) to high-voltage direct current (DC) for efficient, long-distance, or high-capacity power transmission, reconverting it back to alternating current at the destination. High-voltage direct current (HVDC) enables interconnection between asynchronous alternating current grids, supports long-distance submarine cables, and offers lower, more controllable energy losses compared to traditional alternating current.
High-voltage direct current transmission – It is a method for efficiently transmitting large quantities of electricity over long distances or through cables, using direct current (DC) rather than alternating current (AC). It converts alternating current to direct current at the source (rectifier) and back to alternating current at the destination (inverter).
High-voltage switchgear – It is the electrical apparatus which is designed for control of high-voltage circuits.
High voltage system – It defines electrical systems operating above 1,000 volts alternating current or 1,500 volts direct current (sometimes defined above 600 volts in specific codes). It involves engineering, designing, and testing apparatus to manage high electrical stress, reducing transmission losses, and ensuring safety in power networks and industrial applications.
High volume fraction – It refers to a high percentage (above 20 % to 50 %) of reinforcement (fibres or particles) relative to the total volume of a composite material. This concentration increases material density, stiffness, and compressive strength, but can reduce ductility. It defines the transition from diluted to concentrated, high-performance mixtures.
High volume low activity waste – It is a subset of low-level waste (LLW) which is arising from decommissioning activities. Chemical properties of high-volume low activity waste are such that it can potentially be disposed of to a lower level of containment than low-level waste.
High-volume production – It is a manufacturing approach focused on producing large quantities of standardized products, frequently in the thousands or millions, using automated, continuous, or assembly-line processes. This method prioritizes high-speed, cost-efficient, and consistent output, utilizing specialized machinery and rigorous quality control to meet high demand.
High water content – It refers to a high or excessive quantity of water present within a material, such as soil, fuel, or chemical mixtures, relative to its solids or total volume, frequently leading to reduced stability, lower heating values, or operational inefficiencies. It is typically expressed as a percentage of mass, w = (Ww / Ws) x 100 %.
High water pressure – It refers to forces exceeding typical operational, safety, or utility standards, frequently defined as pressure above 6.9 megapascals for industrial, specialized, or cleaning applications. It is the force per unit area (P = F.A) exceeding safe operating limits of pipes and fixtures.
Highway addressable remote transducer (HART) – It is a hybrid industrial protocol which superimposes digital communication signals, using frequency shift keying (FSK), on top of standard 4-20 milli-ampere analog wiring. It enables two-way communication with intelligent field instruments, allowing for remote configuration, diagnostics, and monitoring while retaining legacy analog control systems.
High wind speed – It typically refers to sustained, high-velocity air movement, frequently exceeding 13 meters per second to 18 meters per second, causing substantial structural loading, vibrations, or hazards to infrastructure. Unlike meteorological definitions, engineering focuses on wind pressure (P = 0.5 x air density x velocity-square) and gusts which test structural stability, typically analyzed using wind power density (watts per square meter) and statistical frequency distributions.
Hilbert-Huang transform – It is an adaptive data analysis method for nonlinear and non-stationary engineering signals. It decomposes complex data into ‘intrinsic mode functions’ (IMFs) using ‘empirical mode decomposition’ (EMD), then applies ‘Hilbert spectral analysis (HSA) to calculate precise, time-dependent instantaneous frequencies and amplitudes.
Hilbert spectral analysis – It is a signal processing technique which produces a high-resolution, time-dependent, three-dimensional energy-frequency-time distribution of a signal, important for analyzing nonlinear and nonstationary data. Unlike Fourier analysis, it calculates instantaneous frequencies and amplitudes using the Hilbert transform, typically applied to data decomposed by ‘empirical mode decomposition’ (EMD).
Hilbert transform – In experimental stress analysis and vibration, it is a signal processing technique used to identify system non-linearities, analyze non-stationary signals, and detect damage (e.g., cracks in pipes or fatigue in machinery) by calculating the instantaneous envelope and instantaneous frequency of a raw signal.
Hildebrand solubility parameter (d) – It is a numerical value estimating the solvency behaviour of a specific component, defined as the square root of the cohesive energy density (CED). It indicates the energy needed to break inter-molecular forces (vapourization) per molar volume, predicting that materials with similar ‘d’ values are likely miscible or soluble.
Hill’s yield criterion – It is a criterion used to describe the onset of plastic deformation for anisotropic materials. In its most general form, it assumes the presence of three different axial yield stresses and three different shear yield stresses. The criterion is formulated mathematically so as to reduce to the von Mises yield criterion if the material is isotropic. Developed as an extension of the isotropic von Mises criterion, it uses six constants (F, G, H, L, M, N) to account for differing yield strengths along different axes.
Hindered amines – These are specialized organic compounds where the nitrogen atom is sterically shielded by bulky alkyl or cyclic groups, restricting access to the reactive site. They are mainly used as ‘hindered amine light stabilizers’ (HALS) to protect polymers from UV (ultra-violet) degradation through free radical scavenging, or as selective solvents for removing acidic gases (carbon di-oxide, hydrogen sulphide).
Hindered contraction – It is the contraction where the shape does not permit a metal casting to contract in certain regions in keeping with the coefficient of expansion.
Hindered settling – It is a fluid mechanics phenomenon where high concentrations of particles in a suspension reduce their overall settling velocity because of the collisions, increased fluid viscosity, and upward fluid counterflow. The particles interfere with each other, settling much slower than they settling individually (free settling).
H-infinity design – It refers to a robust control technique used in structural vibration control which is insensitive to disturbances and parametric variations, making it suitable for multiple-input multiple-output (MIMO) systems. This design frequently results in a higher order system, which can be reduced through balanced truncation to maintain performance while simplifying implementation.
Hinge – It is a mechanical bearing which connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other around a fixed axis of rotation, with all other translations or rotations prevented. Hence, a hinge has one degree of freedom. Hinges can be made of flexible material or moving components.
Hinge approach – It refers to a structural modeling method where nonlinear, inelastic behaviour is concentrated at specific, discrete locations (plastic hinges) while the rest of the member is assumed to remain elastic. It simplifies analysis by focusing on moment-rotation curves at joints, making it efficient for earthquake or failure analysis, frequently applied in concrete / steel frame design.
Hinge area – It is the juncture of a hanging burr with the more rigidly adhered portion of a burr.
Hinged arch – It is a curved structural member designed to span openings by supporting loads mainly through compression, featuring pins (hinges) at the supports and sometimes at the crown to allow rotation, manage thermal expansion, and control bending moments. The two main types are two-hinged (base hinges only) and three-hinged (base + crown hinges).
Hinge loss function – It is a widely used loss function in machine learning, particularly for training ‘support vector machines’ (SVMs) and other maximum-margin classifiers. It is designed for binary classification and focuses on ensuring that data points are not only correctly classified but also fall on the correct side of a decision boundary margin.
Hinshitsu-Hozen – It is also known as quality maintenance. It is a pillar of ‘total productive maintenance’ (TPM) focused on achieving zero defects by proactively controlling the conditions of equipment and processes to prevent quality issues. It involves understanding how factors like manpower, materials, machines, and methods interact to cause defects, and then establishing and maintaining conditions which prevent those defects from occurring. Hinshitsu-Hozen aims to create a production environment where defects are eliminated at the source, rather than just being detected and corrected later in the process. It emphasizes understanding how different elements of the production process (the “4Ms”: manpower, materials, machines, and methods) interact and influence quality, and then taking steps to control those interactions.
Hirsch model – It is a combined parallel and series model used for predicting the tensile modulus of short fibre composites, applicable to blends with fibrillar morphology, where the parameter ‘x’ indicates stress transfer influenced by fibril length, orientation, and stress amplification at their ends.
HIsarna process – It is a smelting reduction process for producing liquid iron directly from iron ore fines and coal. It represents a new, potentially more efficient way of making iron and is being developed for substantial reduction of carbon emissions from the ironmaking process. It eliminates prior processing of raw materials as needed by the blast furnace process. The process consists of pre-reduction of iron ore fines in cyclone converter furnace (CCF) of Isarna technology and bath smelting of iron in smelting reduction vessel (SRV) of HIsmelt process. The process name derives by combining the names of the two technologies (‘HI’ from HIsmelt and ‘sarna’ from Isarna, a celtic word for iron). The process cuts both carbon and costs. HIsarna process takes place in a special reactor which has a narrow cyclone furnace on top of a wider convertor.
HIsmelt process – It is an air based direct smelting technology. The process is for the production of liquid iron (hot metal) using iron ore fines or any other appropriate ferrous feed material. The smelting is carried out in a molten iron bath using coal as the reductant and energy source material. The principal raw materials needed for the process are iron ore fines, coal, and fluxes (limestone and dolomite). HIsmelt is short for ‘high intensity smelting’. It is a direct smelting process for making liquid iron straight from the iron ore. The process has been developed to treat iron ore fines with minimum of pre-treatment, making the process more flexible in terms of the quality of iron ore it can treat. The process allows the use of non-coking coal and iron ore fines with significant impurities. The main product of the process is liquid iron or hot metal which can be used in steel melting shop or can be cast in pig casting machine to produce pig iron. The by-product of the process is slag and the off gas.
Histogram – It is a graphical representation (bar chart) of the distribution of data. It is an estimate of the probability distribution of a continuous variable. It is a representation of tabulated frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to the frequency of the observations in the interval. The height of a rectangle is also equal to the frequency density of the interval, i.e., the frequency divided by the width of the interval. The total area of the histogram is equal to the quantity of data. A histogram can also be normalized displaying relative frequencies. It then shows the proportion of cases which fall into each of several categories, with the total area equaling one. The categories are normally specified as consecutive, non-overlapping intervals of a variable. The categories (intervals) are to be adjacent, and are frequently chosen to be of the same. The rectangles of a histogram are drawn so that they touch each other to indicate that the original variable is continuous. Histograms are used to plot the density of data, and frequently for density estimation which is the estimating the probability density function of the underlying variable. The total area of a histogram used for probability density is always normalized to one.
Historical data – It refers to accumulated, time-stamped information regarding past system performance, project metrics, and operational behavior used to analyze trends, validate simulation models, and train predictive algorithms. It comprises structured data (e.g., sensor logs, computer aided design files) and unstructured data (e.g., reports, emails), necessary for optimizing future designs.
Historical development – It defines the evolution of technical knowledge and practice from ancient tool-making to modern, science-based technological systems. It highlights the progression from empirical, trial-and-error methods (e.g., pyramids, aqueducts) to the application of scientific principles, largely driven by the industrial revolution’s need for efficiency.
Historical information – It consists of data from past projects which are used in the planning of future projects of the organization.
Historic estimates – Historic resource quantities frequently possess high uncertainty in respect to geological knowledge regarding quantities and qualities (G-axis), technical feasibility (F-axis), and the environmental-socio-economic axis categories (E-axis). The estimates can be based on an ‘Identified Project’ but until a commercial operator is engaged and has verified or updated the estimates of the quantities, it is probably to be mapped under the ‘Non-Viable Project’ class.
HML analysis – It is a method of analyzing spare parts inventory. This classification is based on the unit price of the spare parts. Under this classification ‘H’ items are those items whose unit cost is very high. ‘M’ items are medium cost spare parts while ‘L’ items are those spare parts whose unit value is low. This type of analysis helps in exercising control at the shop floor level i.e. at the user point. High value spare parts are to be replaced after proper authorization. Efforts are necessary to find out the means for prolonging the life of high value spare parts through reconditioning and repair. Also, it can be worthwhile to apply the techniques of value analysis to find out a less expensive substitute for ‘H’ items.
H-model – It is a two-stage discounted dividend model used to value stocks with high initial growth which declines linearly to a stable rate over a specific period. It calculates intrinsic value by adding the present value of stable growth to the extra value generated by the high-growth phase.
H-performance – It means high performance. It normally describes the ability of a person, organization, system, or machine to operate at an exceptionally high standard, frequently exceeding standard norms, over a long period. It indicates efficiency, speed, and superior quality.
Hob – It is a rotary cutting tool with its teeth arranged along a helical thread, used for generating gear teeth or other evenly spaced forms on the periphery of a cylindrical workpiece. The hob and the Work-piece are rotated in timed relationship to each other while the hob is fed axially or tangentially across or radially into the work-piece. Hobs is not to be confused with multiple-thread milling cutters, rack cutters, and similar tools, where the teeth are not arranged along a helical thread.
Hobbing – It is a specialized, continuous machining process used to create gear teeth, splines, and sprockets by cutting them into a work-piece. It is considered one of the most efficient and cost-effective methods for producing high-quality gears in large quantities, such as spur gears, helical gears, and worm gears.
Hoberman mechanism, Hoberman linkage – It is a deployable mechanism which turns linear motion into radial motion.
Hodograph – It is a vector diagram used to represent the velocity distribution of a moving body, fluid, or deforming material by plotting the locus of the tips of velocity vectors originating from a fixed point. It transforms physical coordinates (x, y, z) into velocity space, mapping movement to analyze kinematics, such as in slip-line field theory for metal forming.
Hodograph plane – It is also called velocity diagram. It is a graphical tool which maps the velocity vectors of a moving fluid or solid body, using velocity components, ‘u, w or v(x), v(y)’, rather than spatial coordinates (x, y). It plots the tip of velocity vectors originating from a central point (the pole) to visualize magnitude and direction changes.
Hoffmann-Sachs approach – It is a foundational analytical method in mechanical metallurgy used to calculate the stresses, pressures, and forces needed for bulk metal deformation processes, such as wire drawing, rolling, and extrusion.
Hoganas process – It is a solid-state, coal-based direct reduction method used mainly to produce high-purity sponge iron powder for powder metallurgy (PM). It involves reducing iron ore (magnetite) using coke, anthracite, and limestone within a tunnel kiln.
Hogging – It means machining a part from bar stock, plate, or a simple forging in which much of the original stock is removed.
Hogging bending moment – It is a negative bending moment in structural engineering which causes a beam or slab to bend into a convex-upward shape (a ‘frown’). It results in tension in the top fibres and compression in the bottom fibres. It normally occurs over supports in continuous beams, at the fixed end of cantilever beams.
Hogging moment – It is a negative bending moment which causes a structural member (like a beam or slab) to bend convex-upward, resulting in compression at the bottom fibres and tension at the top fibres. It typically occurs over interior supports of continuous beams or at the fixed end of a cantilever.
Hogging region – It refers to the section of a structural member (beam or slab) which bends in a convex-upward shape (like a frown or hump) under load, resulting in a negative bending moment. This action causes tension in the top fibres and compression in the bottom fibres, common over supports in continuous beams or at fixed ends.
Hog rings – These are circular mechanisms which securely grip a shaft inside a roller, demanding consistent checks for tightness and integrity to prevent roller malfunction.
Hohenberg-Kohn theorem – It is the foundation of ‘density functional theory’ (DFT), proving that the ground-state properties of a many-electron system are uniquely determined by its electron density ‘n(r)’ rather than the complex 3N-variable wave-function. It reduces the computational complexity of materials by allowing calculations to depend on 3D spatial density, which uniquely defines the system’s external potential, Hamiltonian, and total energy.
Hohman A-6 wear machine – It is a widely used type of wear and friction testing machine in which a rotating ring sample is squeezed between two diametrically opposed rub blocks. This design is said to eliminate shaft flexure such as that found in other machines whose load application from the rub block to the ring is from one side only. Block geometry can be changed from flat to conforming or V-block. This type of machine is designed for use with either lubricated or unlubricated samples.
Hoist – It is a device which is used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It can be manually operated, electrically or pneumatically driven and can use chain, fibre or steel wire rope as its lifting medium. The most familiar form is an elevator, the car of which is raised and lowered by a hoist mechanism. Majority of the hoists couple to their loads using a lifting hook. In mines, it is the machine which is used for raising and lowering of the cage or other conveyance in a shaft.
Hoist, electric – It is a mechanized industrial lifting device powered by an electric motor, designed to raise, lower, and suspend heavy loads using either a steel wire rope or a load chain. It converts electrical energy into mechanical energy to move materials with precision, typically mounted overhead on a fixed structure, monorail, or bridge crane.
Hoisting equipment – It refers to mechanical devices, including cranes, hoists, winches, and jacks, engineered to vertically lift, lower, and position heavy loads safely using ropes, chains, or cables. These devices utilize mechanical advantage (e.g., drum / pulley systems) and are powered manually, pneumatically, or electrically for industrial, construction, and manufacturing tasks.
Hoisting mechanism – It is a device which uses a system of pulleys, cables, or chains to lift and lower heavy loads. It is a unit consisting of a motor drive, coupling, brakes, gearing, drum, ropes, and load block designed to raise, hold, and lower the maximum rated load. It is mounted on the trolley. Hoist mechanism is a fundamental part of machines like cranes, elevators, and other lifting equipment used in several industries. It multiplies the applied force, allowing for the lifting of objects which are too heavy for manual lifting.
Hoist, manual – It is a mechanical, non-powered device designed to lift, lower, or position heavy loads using human effort. It operates through a mechanical advantage mechanism, typically a system of gears, chains, or levers, which multiplies the force applied by the operator, allowing for the handling of loads ranging from a few hundred kilograms to several tons.
Hoist, pneumatic – It is also called air hoist. It is an industrial lifting device powered by compressed air rather than electricity or manual power. It converts pressurized air into mechanical energy (rotation or linear motion) to lift, lower, and position heavy loads. These devices are frequently used in demanding industrial environments, such as manufacturing plants, shipyards, mining, and chemical processing, because of their safety, high duty cycles, and durability in harsh conditions.
Hoist, hydraulic – It is a lifting device which utilizes pressurized, incompressible fluid (typically oil) within a closed system to raise, lower, or move heavy loads vertically. It operates on Pascal’s law, which states that pressure applied to a confined fluid is transmitted equally in all directions, allowing a small input force to be amplified into a much larger output force.
Hold capacitor – It is a critical component in sample-and-hold circuits, designed to store an analog voltage signal for a specific duration. Engineered for high precision, these capacitors feature extremely low leakage and minimal dielectric absorption to prevent voltage droop or contamination of new samples, ensuring accurate, stable data retention in analog-to-digital converters and signal processing applications.
Hold circuit – It is an electrical circuit which retains a sampled input voltage for a specific duration, utilizing a capacitor to store electrical charge and a transmission gate to control the switching between sample and hold states.
Hold down – It is frequently called a blank holder or pressure pad. It is a tool component used to apply, uniform compressive pressure to a sheet metal blank against the die surface during operations like deep drawing. Its main function is to restrict the material from lifting and to control the flow of metal into the die cavity, preventing defects such as wrinkling. In structural engineering, hold-downs are specialized steel connectors used to anchor wall framing (wood or cold-formed steel) to a foundation or floor system, providing critical tension / uplift resistance against overturning moments caused by wind or seismic forces. They are mainly installed at the end studs of shear walls.
Hold down mechanism – It consists of devices which are used to secure objects on a conveyor and prevent unintended movement, necessitating regular evaluations for proper functioning and adjustments based on material characteristics.
Hold-down plate (pressure pad) – It is a pressurized plate designed to hold the work-piece down during a press operation. In practice, this plate frequently serves as a stripper and is also called a stripper plate.
Holder-and-sleeve dies -These refer to a tooling assembly approach where the active die insert (the part which shapes the metal) is encased within a supporting structure, normally a sleeve, and held securely within a die holder, die shoe, or bolster. This design is mainly used in extrusion, high-pressure die casting, and powder metallurgy to provide the structural support necessary to withstand high pressures, ensure precise alignment, and allow for the easy replacement of worn, expensive die materials.
Holder / wrap multiple-insert die system – In metal stamping and casting, it is a modular tooling assembly where a master holder (the ‘holder’ or ‘wrap’) securely houses several replaceable, smaller die components (the ‘inserts”) in one work-station. This design allows a single press stroke to produce multiple parts or perform multiple operations, improving productivity while reducing costs associated with manufacturing complex, solid, single-piece dies.
Holding – In heat treating of metals, it is that portion of the thermal cycle during which the temperature of the object is maintained constant.
Holding capacity – It normally refers to the maximum load, volume, or substance a system, material, or structure can retain, support, or contain under specific conditions before failure or saturation. Common contexts include anchor pull-out resistance, soil moisture retention, or container volume.
Holding chamber – It is a refractory-lined vessel designed to receive, hold, and maintain molten metal at a specific, controlled temperature before it is cast or processed.
Holding devices – These are the fixtures used to connect fabrications / parts to the handling equipment in the facility.
Holding force (Fm), magnet – It is the force perpendicular to the attraction faces needed to hold the attracted piece. It is normally shown in the specification sheets of the magnets and it refers to the whole contact face. The holding force for a magnet is affected by the composition of the material being lifted. Alloys with higher iron content are typically more susceptible to magnetic fields than those with lower iron content.
Holding furnace – It is a furnace into which molten metal can be transferred to be held at the proper temperature until it can be used to make castings. It serves as a buffer between the melting furnace and casting machines.
Holding ladle – It is a refractory-lined, frequently covered, steel vessel designed to receive, store, and maintain molten metal at a specific, consistent temperature after melting and before casting. It acts as a buffer between the furnace and the moulding line, ensuring a continuous supply of metal for casting while allowing for treatments like alloying or degassing.
Holding temperature – In heat treating of metals, it is the constant temperature at which the object is maintained.
Holding time – It is the time for which the temperature of the heat-treated metal object is maintained constant. It frequently referred to as soaking time. It is the specific duration a material is maintained at a precise, high temperature during the heating process. This important phase ensures the entire component reaches a uniform temperature, allowing for necessary homogenization throughout.
Holding torque – It is the maximum static torque (rotational force) an energized motor, typically a stepper motor, can withstand without rotating from its current position. It defines the motor’s ability to resist external loads while stopped, measured in Newton meter (N.m), and is an important metric for ensuring positional accuracy.
Holding vessel – It is a container which is designed to temporarily store a substance, such as a liquid, gas, or heat / cold medium, for short or long-term purposes. It can also be referred to as a holding tank.
Holding voltage – It is the minimum voltage needed to maintain a component or device in its active, closed, or ‘on’ state after initial activation. It is lower than the initial pickup / trigger voltage, frequently used in relays, contactors, ‘silicon-controlled rectifiers’ (SCRs) /thyristors, and ESD (electrostatic discharge) protection circuits to ensure stability and reduce power consumption.
Holdup time – It is the duration (normally in milli-seconds) which a unit maintains its output voltage within specified regulation limits after losing its input power. It serves as a buffer against AC (alternating current) mains interruptions or dips, allowing connected systems to continue running or safely shut down without rebooting. It is also the time needed for an infinitesimal quantity of non-absorbed gas to pass through a chromatographic system, which is necessary for calculating thermodynamic properties and retention indices of the separation system.
Holdup volume – It refers to the total volume of fluid (liquid or gas) contained within a system, such as a packed column, pipe, or reactor, at any given operating moment. It is critical for calculating retention time, pressure drops, and efficiency in separation processes.
Hole – It is a void in rolled product. Typical cause of it is a non-metallic inclusion during rolling. Hole is also normally an opening, cavity, or depression created in or through a solid metal work-piece. These are foundational features used to enable functional assembly, weight reduction, fluid transport, or positioning. Holes are classified based on their geometry and purpose, with common types include (i) through hole, (ii) blind hole, (iii) threaded / tapped hole, (iv) counter-bore hole, (v) counter-sink hole, and (vi) reamed hole.
Hole axis – It is the theoretical centre-line defining the central, longitudinal axis of a cylindrical hole, serving as a critical reference for alignment, positioning, and fastening. It is mathematically defined by a point and a unit direction vector, crucial for calculating concentricity or position in GD&T (geometric dimensioning and tolerancing).
Hole basis system – It is a standard, economic, metrology method in mechanical engineering where the hole size is kept constant (fixed) as the reference, while the shaft size is varied to achieve different fits (clearance, transition, or interference). The hole’s lower deviation is zero, meaning the minimum hole size equals the nominal size.
Hole capture cross-section – It is a parameter defining the effective target area of a defect or trap for catching a free hole in a semiconductor, quantifying the probability of carrier recombination or trapping. It is measured in square centimeter.
Hole coalescence – It is also called micro-void coalescence. It is the final stage of ductile fracture, where microscopic voids, formed around inclusions or second-phase particles, merge together to create a continuous crack, leading to material failure. This process is characterized by high energy absorption, resulting in a dimpled surface morphology.
Hole concentration – It is the density of empty, positively charged electronic states (holes) in the valence band of a semiconductor, measured in units of per cubic centimeter. It represents the number of mobile positive charge carriers per unit volume, acting as majority carriers in p-type semiconductors and minority carriers in n-type, important for determining electrical conductivity.
Hole conductor – It is a material which facilitates the movement of positive charge carriers (holes) in a semiconductor, crucial for p-type conduction in transistors, diodes, and solar cells. Holes are quasiparticles representing electron vacancies in the valence band, which move in the opposite direction of electrons under an applied electric field.
Hole depth i- It is the vertical or axial distance from the entry surface of a work-piece to the bottom of the cavity. It is a critical parameter for functionality, ensuring that fasteners, components, or fluids can fit properly without damaging the part.
Hole diameter – It is the measurement across the widest point of a cylindrical opening, representing the nominal size of a drilled, bored, or machined hole, frequently denoted by the diameter symbol ‘phi symbol in upper case’ on technical drawings. It specifies the intended size, including needed tolerances, to ensure proper fit for fasteners, pins, or components.
Hole drilling – It is a machining process which creates, enlarges, or finishes a cylindrical hole in a work-piece by removing material using a rotating, multi-point cutting tool (drill bit). It is mainly used for assembling components through fasteners, creating cooling channels, or alleviating structural stress by blunting crack tips.
Hole-drilling strain-gauge technique – It is a semi-destructive method used to measure residual stresses in materials. It involves drilling a small hole into a material while simultaneously monitoring strain changes around the hole using strain gauges, typically in a rosette configuration. By analyzing the strain relaxation around the hole, the magnitude and direction of the residual stresses can be determined.
Hole-drilling method – It is a widely used semi-destructive for measuring residual stresses in materials. It involves drilling a small, typically 1 millimeter to 4 millimeters diameter blind hole into a component’s surface and analyzing the resulting strain relief, measured by strain gages to determine stress magnitude and direction.
Hole-drilling technique – It is a method used to measure residual stresses in materials. It involves drilling a small hole into a component and measuring the resulting strain changes on the surface around the hole. These strain measurements are then used to calculate the magnitude and direction of the residual stresses which are present before the hole has been drilled.
Hole enlargement – It is the precision machining process of increasing the diameter of an existing pre-drilled, cast, or punched hole to a specific size, improving accuracy and surface finish. Common techniques include reaming (for slight, high-accuracy finishing), boring (for larger, single-point tool resizing), and trepanning (for large diameter, core-removing cuts).
Hole expansion – It refers to the process of increasing the diameter of a pre-existing hole in a metal sheet using a punch (typically conical) to test or improve material ductility and edge stretch-flangeability. It is widely used to measure edge crack sensitivity in high-strength steels, with the expansion quantified as a percentage ratio, known as the ‘hole expansion ratio’ (HER) or ‘lambda’.
Hole expansion ratio (lambda) – It is a metric used to quantify the edge-stretching capacity and stretch-flangeability of sheet metal. It measures the percentage increase of a hole’s diameter when expanded by a conical punch until cracks appear. A higher ‘hole expansion ratio’ (HER) indicates better resistance to edge cracking.
Hole expansion test – It is a simulative test in which a flat metal sheet sample with a circular hole in its centre is clamped between annular die plates and deformed by a punch, which expands and ultimately cracks the edge of the hole.
Hole flanging – Holes can be flanged, or collared, to strengthen them and to provide an area for threading, if needed. Collaring is accomplished by hole punching and expansion or by piercing and expansion. Hole flanging is the forming of an integral collar around the periphery of a previously formed hole in a sheet metal part.
Hole heating – It refers to the process of adding heat to a hydrate reservoir, typically through methods such as steam or hot water injection, to induce the dissociation of hydrates and facilitate gas production. This technique can involve several designs for down-hole heating units aimed at improving energy efficiency while managing production issues associated with hydrate stability.
Hole plate – It is a steel sheet or plate featuring one or more drilled, punched, or cut holes, mainly used in structural applications for joining components, distributing loads, or reducing structural self-weight. These plates are important in fastening systems (e.g., bolting, riveting) and frequently experience stress concentrations which need careful analysis, particularly in fatigue scenarios. Hole plate is also a steel sheet, typically with a central hole, used in rock-bolt applications to distribute loads. It can be flat or domed, with domed plates offering higher deformation capacity and reduced risk of punch-through failure under load.
Hole punching – Hole making in sheet metal involves the use of a punch and die to separate a slug from the sheet by shearing. After a small amount of plastic indentation by the punch, severe shearing deformation occurs between the punch edge and the die corner. Cracks begin to form within this shear zone at the punch and die corners and then progress toward each other. Final separation of the slug from the sheet involves tearing, resulting in a burr around the exit perimeter of the hole.
Hole radius (R) – It is the linear dimension from the central axis of a hole to its edge, representing half the diameter (D/2). While holes are typically dimensioned by diameter (phi symbol in upper case) in technical drawings, radius is used for rounded cutouts, fillets, or specific stress calculations (r) where the curvature is important.
Hole structure – It refers to the specific geometry, size, depth, and orientation of these features, which determine the component’s functionality and stress concentration, frequently denoted in drawings with a diameter symbol (phi symbol in upper case). Hole structure is also the arrangement of casing and bit sizes in drilling operations, which influences the matching degree of tools and the quality of cement jobs, as well as the overall feasibility of downhole operations.
Hole system – It is also called hole basis system. It is a tolerance methodology where the hole size is kept constant (fundamental deviation is zero) and the shaft size is varied to achieve the desired fit (clearance, transition, or interference). It is preferred in mass production for efficiency, since it allows for standard drills / reamers to be used, with shaft dimensions adjusted by machining.
Hole task – It involves precisely defining the geometric, spatial, and process-oriented work-piece attributes such as cavity or aperture (normally circular) formed for functional, assembly, or weight-reduction purposes, to ensure proper fit, function, and manufacturability.
Hole temperature – It refers to the temperature of the wellbore, frequently measured at the bottom (‘bottom-hole temperature’, BHT). It represents the thermal state of the drilling fluid, tools, and surrounding formation, which is influenced by depth, geothermal gradients, and mud circulation.
Holey fibre – It is a type of micro-structured optical fibre. These fibres are waveguides defined by a microscopic array of air holes running along the entire length of a cladding, typically surrounding a solid or hollow core. Engineered using materials like silica, they guide light through photonic bandgap effects (periodic holes) or average index effects (modified total internal reflection, TIR). Key properties include high nonlinearity, controllable dispersion, and end-less single-mode operation, making them vital for telecommunications, fibre lasers, and sensing.
Holey graphene – It is also called graphene nano-mesh. It is a 2D structural derivative of graphene characterized by in-plane nanometer-sized pores within the hexagonal carbon lattice. These intentionally introduced holes create high-density edges and increase surface area, enabling tunable electronic, catalytic, and transport properties for applications like lithium-ion batteries, super-capacitors, and molecular filtration
Holidays – These are discontinuities in a coating (such as porosity, cracks, gaps, and similar flaws) which allow areas of substrate to be exposed to any corrosive environment which contacts the coated surface.
Holistic design – It is an integrated, systems-thinking approach which considers a product, system, or structure as an inter-connected whole rather than a collection of isolated parts. It collaboratively merges multi-disciplinary expertise, spanning technical, environmental, social, and user-experience factors, to ensure long-term sustainability, functionality, and, harmony.
Hollandite – It is a silvery-gray to black barium-manganese oxide mineral, Ba[(Mn6)4+(Mn2)3+]O16, known for its distinctive monoclinic, frequently radiating, acicular crystal habit. Its structure consists of double chains of MnO6 octahedra delimiting 2 × 2 tunnels. The electrostatic charge created by the Mn3+ for Mn4+ substitution is balanced by cations in the tunnels. As a member of the coronadite group, it typically forms in manganese deposits as a primary or secondary, weathering-related mineral. It is frequently found as black star-like inclusions in quartz.
Hollow cathode – It is made of a single element or alloy of the element to be analyzed to ensure sharp analytical lines with an absolute minimum of interfering spectral components.
Hollow cathode lamp – It is a type of glow discharge tube which uses a hollow cathode to improve the emission intensity.
Hollow core fibre – It is an advanced type of optical fibre which, unlike conventional fibre, guides light within a central hollow channel (air or vacuum) rather than a solid glass core. The core is surrounded by a complex, micro-structured cladding, typically made of pure silica glass, which uses either photonic bandgap effects or anti-resonant (inhibited coupling) mechanisms to confine the light.
Hollow drill test – It is also known as hollow drill sampling. It is a semi-destructive, material-testing technique used to determine the local material properties (such as fatigue strength or microstructure) of a cast component without destroying the entire casting. In this test, a hollow tool (frequently diamond-coated) is used to drill into a specific, frequently critical, location of a casting, producing a small, cylindrical sample. This method is used to analyze the local microstructure or mechanical properties (e.g., tensile or fatigue strength) of specific, complex sections of a casting, rather than just the average properties.
Hollow fibre – It is an artificial, tubular, and porous micro-filaments featuring an empty central core and a rigid, high-surface-area shell. Mainly manufactured from polymers (e.g., poly-ether-sulfone) through spinning, hollow fibres are used as semi-permeable membranes for separation processes, filtering, and bio-reactors because of their high packing density.
Hollow fibre membrane module – It is a high-packing-density filtration device containing thousands of parallel, self-supporting polymeric or ceramic micro-tubes (typically 50 micro-meters to 200 micro-meters in diameter) potted in a housing. It is engineered for high-flux, selective separation of gases or liquids, utilizing low mass-transfer resistance and large surface areas within a small volume.
Hollow fibre membranes – These are self-supporting, capillary-shaped polymeric tubes (50 micro-meters to 1,000 micro-meters in diameter) designed for high-efficiency separation processes, offering high packing density (surface area-to-volume ratio) and high flux. They feature asymmetric micro-porous structures, operating through pressure-driven filtration (micro-filtration /ultra-filtration, reverse osmosis) or gas separation, with the feed stream normally passing on the outside.
Hollow fibre module – It is a compact filtration unit containing thousands of thin, self-supporting polymeric or ceramic fibres (50 micrometers to 200 micrometers in diameter) housed within a shell. Engineered for high-surface-area-to-volume ratio, it enables efficient liquid / gas separation, and water treatment through inside-out or outside-in flow, allowing high flux and low pressure operation.
Hollow forging – It is a hot or cold metalworking process used to produce hollow, cylindrical, or tubular components by expanding or drawing a pre-punched metal billet over a mandrel, frequently within an open-die setting. It increases material strength and reduces weight, with up to 70 % material savings compared to machining, making it ideal for high-stress applications like shafts, rings, and pressure vessels.
Hollow nano-structures – These are nano-materials with a tubular or shell-like structure which contains an empty interior, providing a large surface area for charge storage. Hollow nano-structures are advanced, engineered functional materials (1 nano-meter to 1,000 nano-meter range) characterized by a solid, frequently porous, outer shell enclosing an empty void or inner cavity. These structures feature high specific surface areas, low density, and high loading capacity, making them superior to solid counterparts for applications in energy storage, catalysis, and sensing.
Hollow profiles – These are structural metal components characterized by a hollow cross-section—containing a continuous, empty interior space (void) which runs the entire length of the component. Unlike solid bars or rods, these profiles are designed for high strength-to-weight efficiency, making them important for applications which need structural integrity with reduced weight. They are widely used in construction, automotive engineering, machinery, and furniture fabrication.
Hollow shaft – It is a cylindrical machine element with an empty, tubular core (D1 is less than D0) designed to transmit torque and rotational motion while minimizing weight. By removing low-stress material from the centre, these shafts offer higher strength-to-weight ratios and increased polar moment of inertia compared to solid shafts, making them ideal for high-speed applications.
Hollow silica nano-spheres – These spherical, inorganic nano-materials featuring a hollow core surrounded by a solid or porous silica (SiO2) shell. They are characterized by low density, high surface area, and high loading capacity, normally engineered through template-based synthesis (e.g., poly-styrene cores) for thermal insulation, and catalysis.
Hollow structural section – It is a type of metal profile with a hollow cross-section. Hollow structural section members can be circular, square, or rectangular sections, although other shapes such as elliptical are also available. These sections are normally made from structural steel.
Hollow tube – It is frequently referred to as a hollow structural section or HSS. It is a structural member characterized by a hollow cross-section, normally circular, square, or rectangular, designed for high strength-to-weight efficiency in construction, fabrication, and mechanical applications. Unlike solid bars, hollow tubes provide superior torsional resistance and load-bearing capacity while using less material.
Hollow tubing springs – These can be either extension springs or compression springs. Hollow tubing is filled with oil and the means of changing hydrostatic pressure inside the tubing such as a membrane or miniature piston etc. to harden or relax the spring, much like it happens with water pressure inside a garden hose. Alternatively, tubing’s cross-section is chosen of a shape which it changes its area when tubing is subjected to torsional deformation: change of the cross-section area translates into change of tubing’s inside volume and the flow of oil in / out of the spring which can be controlled by valve thereby controlling stiffness. There are several other designs of springs of hollow tubing which can change stiffness with any desired frequency, change stiffness by a multiple or move like a linear actuator in addition to its spring qualities.
Hollow valve – It is a high-performance internal combustion engine valve featuring a hollow stem (and sometimes head) to considerably reduce mass, frequently by 20 % or more, allowing higher revolutions per minute (rpms) without increasing valve train loads. Frequently filled with sodium, the hollow cavity serves as a heat exchanger to lower exhaust valve operating temperatures.
Hologram – It is a physical recording of an interference pattern which reproduces a 3D light field using diffraction, rather than lenses. It records both the intensity and phase of light waves reflected from an object, allowing for true depth, parallax, and realistic 3D representation without special glasses.
Holographic display – It is an advanced imaging system which utilizes diffraction and interference of coherent light (lasers) to reconstruct a 3D light field, allowing viewers to see true three-dimensional, high-fidelity, glasses-free images. Unlike stereoscopic 3D, it eliminates vergence-accommodation conflict by providing proper depth cues.
Holographic interferometry – It is a non-destructive testing technique that uses holography to measure deformations, vibrations, and strains on objects. It works by creating interference patterns between light waves recorded in a hologram and light waves interacting with the object in real-time. These interference patterns reveal subtle changes in the object’s surface, allowing for precise measurements of even minute displacements.
Holographic non-destructive testing – It is an effective technique for use with metal welded or braze bonded components, frequently with complex geometries. A single large ultrasonic transducer which sends out ultrasonic waves towards the object under study and it scans the object. The scattered waves from the object from the object waves. A received transducer collects the scattered object wave and converts them into electrical signals. The reference electrical waves are given by the radio frequency (RF) oscillator and these object to reference waves are made to interference by the electronic adder. The interference pattern is formed on the fluorescent screen of the cathode photographic film is developed. The developed photographic film serves as a hologram. The hologram is illuminated by a low power laser which acts as the optical reference source. The television camera takes the video-graph of the 3 D image of the object and it displays on the television monitor.
Holographic speckle-interferometry – It is a non-destructive testing technique which combines holographic interferometry and speckle interferometry to measure static and dynamic displacements and deformations of objects with rough surfaces. It utilizes laser light and interference patterns to detect even minute changes in surface shape or position, providing high-precision measurements at the wavelength of light.
Home scrap – It refers to the scrap metal generated within a steel plant or a foundry during the manufacturing process and then immediately recycled back into the same facility. It includes materials like trimmings, punchings, and borings. Since it is recycled on-site, its chemical composition is typically well-known, making it easy to integrate back into the production cycle.
Homodyne detection – It is a measurement technique which involves mixing a quantum system with a strong coherent state at a beam splitter and measuring the intensity difference at the output, which can be destructive or non-destructive depending on the method used. It is normally applied in optical domains and can achieve high efficiency, typically exceeding 90 %.
Homoepitaxial growth – It is an engineering process which deposits a crystalline thin film onto a substrate of the same material (e.g., silicon on silicon, gallium nitride on gallium nitride) to produce high-purity, structurally perfect epitaxial layers. It enables the creation of uniform films, precise doping profiles, and improved electrical properties in semi-conductor devices.
Homogenate – It is a uniform mixture or suspension created by mechanically disrupting and breaking down raw material into smaller particles, ensuring consistency in composition. This fluid is frequently used for further analysis or processing.
Homogeneity – This term is used in statistics to describe samples or individuals from populations, which are similar with respect to the phenomenon of interest. If the populations are similar then they are said to be homogenous, and by extension, the sample data is also said to be homogenous.
Homogeneous – It is the descriptive term for a material of uniform composition throughout. It is a medium which has no internal physical boundaries. Homogeneous is a material whose properties are constant at every point, i.e., constant with respect to spatial coordinates (but not necessarily with respect to directional coordinates).
Homogeneous alloy – It is a single-phase solid solution composed of two or more metallic elements (or a metal and a non-metal) uniformly distributed at the atomic level. It acts as a single substance with consistent properties throughout, such as brass (copper-zinc) or bronze, typically designed to improve strength or corrosion resistance.
Homogeneous boundary condition – It is a type of boundary constraint where the dependent variable (e.g., temperature, displacement) or its derivative is set to zero on the boundary of a domain (u =0, or du/dn = 0). It represents a ‘zero-value’ or ‘no-flux’ condition, normally used in differential equations, ‘finite element analysis’ (FEA), and heat transfer.
Homogeneous carburizing – It is the use of a carburizing process to convert a low-carbon ferrous alloy to one of uniform and higher carbon content throughout the section.
Homogeneous case – It refers to a system, substance, or model characterized by uniform properties, composition, or structural characteristics throughout its entire domain. The opposite is a heterogeneous case, which features non-uniform, distinct phases or properties.
Homogeneous catalyst – It is a substance, such as a soluble metal complex or acid, which exists in the same phase as the reactants (typically liquid or gaseous). By operating in the same phase, these catalysts offer high selectivity and uniform active sites, making them ideal for specialized, smaller-scale, or fine chemical synthesis, though they are difficult to separate from products.
Homogeneous charge compression ignition – It is an advanced internal combustion engine technology which combines spark-ignition (SI) homogeneous mixture preparation with diesel-like compression ignition (CI). It features a premixed, lean fuel-air charge that auto-ignites through compression, allowing for ultra-low nitrogen oxides (NOx) and particulate matter emissions while achieving high, diesel-like efficiency.
Homogeneous combustion – It refers to a process where gaseous fuel and oxidizer (air) are thoroughly mixed at the molecular level prior to ignition, resulting in a uniform, volumetric, and rapid combustion throughout the chamber without a distinct propagating flame front. It is normally used to reduce nitrogen oxides (NOx) and soot emissions, frequently found in lean-premixed systems engines.
Homogeneous compression – It refers to a combustion process where a uniform, premixed, and typically lean mixture of fuel and air is compressed to the point of auto-ignition. It is an advanced, low-temperature combustion (LTC) mode which merges the characteristics of spark ignition (premixed charge) and diesel engines (compression ignition) to achieve high thermal efficiency with considerably lower nitrogen oxides (NOx) and particulate matter (soot) emissions.
Homogeneous coordinates – These are a projective coordinate system used in engineering (robotics, computer vision, graphics) which represent n-dimensional points using n + 1 coordinates, adding a scaling factor (w). They allow affine transformations, rotation, translation, scaling, and projection, to be represented consistently using matrix multiplication, converting, for example, 3D translation into a 4×4 matrix operation.
Homogeneous deformation – It is the uniform change in shape and size of a material across its entire volume, where straight lines remain straight and parallel lines remain parallel after loading. It represents a uniform strain state without localized deformation or shear, characterized by a constant deformation gradient tensor (F). It is the uniform deformation of a sample at a macroscopic scale, where the shape and size of the cross-sections change simultaneously along the loading axis without observed macroscopic shear localization.
Homogeneous dispersion – It is the uniform, consistent distribution of fine particles, fillers, or additives (dispersed phase) within a continuous matrix (solvent or polymer) throughout the entire volume. It ensures no visible separation, identical properties at any point, and is critical for stability in nano-composites, colloids, and mixtures.
Homogeneous distribution – It refers to the uniform, consistent, and even spread of components, particles, or properties (such as density, temperature, or concentration) throughout a material or system. It indicates that no substantial differences or deviations exist in any part of the system.
Homogeneous effective medium – It is an idealized, uniform continuum used to represent a physically heterogeneous, multi-phase material (such as an alloy, composite, or multi-phase micro-structure). It is a modeling approach which allows calculation of macroscopic, averaged properties (like elastic modulus, thermal conductivity, or electrical resistivity) of a complex mixture without needing to simulate the exact, minute details of every grain, phase boundary, or inclusion. Homogeneous effective medium is an idealized, uniform material representation used to simplify the analysis of complex, heterogeneous, or composite structures. By averaging properties, such as density, elasticity, or permittivity, over a volume, it treats multi-phase materials as a single-phase material with consistent, homogenized characteristics.
Homogeneous equation – It refers to a system of linear equations where all constant terms are zero (Ax = 0), or a differential equation where all terms contain the dependent variable or its derivatives, resulting in a zero right-hand side. These equations represent systems in balance or equilibrium, where the trivial solution (x = 0) is always present.
Homogeneous flow – It is sometimes used to denote a flow with negligible relative motion. Several bubbly or mist flows come close to this limit.
Homogeneous flow model – It treats two-phase mixtures (e.g., liquid-vapour) as a single-phase fluid with averaged properties, assuming both phases travel at the same velocity (no-slip condition). It is effective for high mass flux, well-dispersed flows like bubble or annular flow.
Homogeneous fluid – It is a single-phase substance or mixture with uniform physical properties (density, viscosity, composition) throughout its volume, meaning no internal interfaces exist. It allows for modeling fluid dynamics, such as through the Navier-Stokes equations, by assuming constant properties at a given state.
Homogeneous formation – It refers to a rock formation with uniform petrophysical properties, such as porosity, permeability, and thickness, which do not change with location in the reservoir. While this ideal scenario rarely exists in nature, it is a foundational assumption for simplifying flow models.
Homogeneous gas reaction – It is a chemical process where all reactants and products exist in a single, uniform gaseous phase. These reactions are characterized by the absence of phase boundaries, allowing molecules to mix uniformly, typically occurring at high temperatures (e.g., combustion or hydrocarbon cracking).
Homogeneous group – It is a group of employees who experience similar work-place conditions, tasks, and exposure levels during a specified period. These groups are defined by consistent, uniform exposure, allowing them to be analyzed as a single unit, frequently performing identical, repetitive duties in the same environment.
Homogeneous half-space – It is a semi-infinite, continuous, and isotropic medium with uniform physical properties (e.g., density, elasticity, wave velocity) throughout its entire volume, bounded by a single plane surface. It is a modeling concept used to simplify analysis, such as in geotechnical, civil, and geophysical engineering for stress / wave propagation.
Homogeneous isotropic turbulence – It is an idealized, simplified form of turbulence where statistical properties are uniform throughout the fluid (homogeneous) and independent of direction (isotropic). It lacks shear and preferred orientation, making it the fundamental model for analyzing small-scale, universal energy cascade processes in fluid dynamics.
Homogeneous layer -It is a material section, coating, or zone with uniform physical, chemical, and mechanical properties throughout its entire volume. It is defined by consistent density, composition, and structure which do not vary with position or thickness. These layers are used to simplify modeling in structural analysis, fluid flow, and material science.
Homogeneous medium – It is a material or system with uniform, identical physical and chemical properties (e.g., density, elasticity, index of refraction) at every point throughout its entire volume. Such media lack internal irregularities or structural variations, simplifying analysis in heat transfer, mechanics, and wave propagation.
Homogeneous membranes – These are dense, non-porous films which separate chemical species based on solubility and diffusivity rates within the membrane matrix, rather than by physical pore sieving. As opposed to heterogeneous types, these materials appear uniform at microscopic levels, with transport driven by diffusion, and are used extensively in gas permeation, and pervaporation separation.
Homogeneous model – It is a simplified representation of a system which assumes uniform properties, composition, or phase behaviour throughout, neglecting spatial distribution or differences between constituents. It frequently treats complex mixtures (like two-phase flow) as a single-phase fluid with averaged properties, typically assuming no slip between phases and thermodynamic equilibrium.
Homogeneous multi-task system – It refers to a computing environment or, more broadly, a system of agents where all processing units (or components) are identical in functionality, performance, and characteristics. In this setup, any given task or thread can be executed on any available processor with similar performance, power consumption, and execution time. Homogeneous multi-task system is composed of multiple agents which possess similar dynamics and characteristics, allowing them to collaborate effectively in performing complex tasks within several applications.
Homogeneous nucleation – It is the spontaneous, uniform formation of a new phase’s nuclei (e.g., solid crystals) within a parent phase (e.g., pure liquid) without the aid of impurities or surfaces. It needs high undercooling to overcome the high free energy barrier associated with forming a new interface.
Homogeneous plate – It is a structural component with consistent material properties (such as density, elasticity, and strength) throughout its entire volume, specifically uniform across its thickness. Unlike composite or layered materials, a homogeneous plate is single-layered and behaves identically regardless of the location tested.
Homogeneous Poisson process – It is a statistical model which describes the occurrence of random events over time, characterized by the isolation of events and their random, independent generation at a uniform mean rate. In this process, the number of events in a given time interval follows a Poisson distribution.
Homogeneous problem – It refers to a scenario, equation, or system where all terms are of the same degree or where the system represents a natural state without external, non-zero forcing functions. It implies uniformity and proportionality, which simplifies mathematical modeling, allowing engineers to determine the fundamental characteristics of a system before applying external loads or inputs.
Homogeneous regime – In bubble columns and reactor design, it refers to a flow condition at low gas velocities characterized by uniformly sized, small bubbles dispersed evenly throughout the liquid. It is a single-phase-like flow, where bubbles are uniform in size, no significant radial gas hold-up profiles exist, and no large-scale liquid circulation is present.
Homogeneous region – It is a defined area, material, or system showing uniform physical, hydrological, or structural properties throughout its volume. It implies consistency in specific characteristics, such as soil, rainfall, or stress distribution, allowing for accurate modeling, analysis, and extrapolation of data within that zone.
Homogeneous rock – It refers to geological material with uniform physical properties, chemical composition, and texture throughout its structure. It implies the absence of substantial variations in composition or structure, ensuring that mechanical properties (like strength and density) do not change with position.
Homogeneous segment – It is a portion of a system, material, or dataset which shows consistent, uniform properties or characteristics throughout its structure. It is defined by internal consistency, frequently measured by a cost function, or by having identical chemical / physical properties throughout its volume.
Homogeneous structure – It refers to a metallic material which possesses a uniform chemical composition and crystal structure throughout its entire bulk. This means that every part of the material shows identical physical and mechanical properties, with no visible boundaries, phase separation, or substantial segregation of alloying elements.
Homogeneous substance – It is a material with a uniform composition, structure, and physical properties (like density, strength, or conductivity) throughout its entire volume, regardless of which part or orientation is sampled. It consists of a single phase where components are evenly distributed and indistinguishable, such as in pure metals, alloys, or, when viewed at a proper scale, specialized materials.
Homogeneous turbulence – It is a type of turbulent flow where statistical properties, such as kinetic energy, eddy size, and velocity fluctuations, are uniform and independent of position throughout the flow field. It assumes the flow is spatially invariant, simplifying theoretical analysis, and is frequently used to study turbulence away from boundaries.
Homogeneous void fraction – It is the ratio of gas volume to total volume in a two-phase flow, calculated assuming both phases travel at the same velocity (zero slip). It represents a simplified model where the gas and liquid are treated as a thoroughly mixed pseudo-fluid, frequently used for bubbly or mist flows.
Homogeniser – It is defined as a device used to create a uniform mixture by breaking down particles or droplets within a substance, ensuring consistency in the physical properties of materials, which is important for applications in different industries, including those utilizing hemp concrete and lime binders.
Homogenization – It is a process, either physical or computational, which creates a uniform, consistent material or mixture by reducing particle size, breaking down immiscible phases, or averaging micro-structural properties. It ensures uniform distribution, stability, and consistent texture in emulsions or calculates effective material properties for heterogeneous structures.
Homogenization, fluid / process engineering – It involves passing fluids under high pressure (10 mega-pascals to 20 mega-pascals) through a small orifice to reduce particle / globule size to a uniform, fine level. The process utilizes shear, turbulence, and cavitation to break particles.
Homogenization heat treatment – It is a thermal process where cast alloys (particularly aluminum and steel) are heated to high temperatures, typically between 450 deg C to 600 deg C, just below the solidus temperature, for an extended period, followed by controlled cooling. The objective is to redistribute alloy elements uniformly (remove segregation) and reduce directionality in the micro-structure.
Homogenization treatment – It is a high-temperature metallurgical process used to eliminate chemical segregation (micro-segregation) in alloys, particularly aluminum castings, by promoting atomic diffusion. It involves heating the material close to its melting point (e.g., 480 deg C to 540 deg C for aluminum) to ensure uniform distribution of alloying elements, resulting in a stable, more ductile, and less directionally sensitive micro-structure.
Homogenized ingots -These are cast metal blocks (typically aluminum, steel, or superalloys) which have undergone a high-temperature heat treatment process to eliminate micro-segregation, reduce chemical nonuniformity, and break down or redistribute brittle intermetallic phases. This process, known as homogenization heat treatment, allows alloying elements to diffuse evenly throughout the solid solution, improving the material’s structural consistency and improving its workability for subsequent deformation processes like forging, rolling, or extrusion.
Homogenizer – It is a device, frequently a specialized high-pressure pump, designed to create uniform mixtures, emulsions, or suspensions by breaking down particles or fat globules within a liquid. It works by forcing substances through narrow openings or valves, subjecting them to intense shear, cavitation, and impact forces.
Homogenizing – It is a heat-treating practice whereby a metal object is held at high temperature to eliminate or decrease chemical segregation by diffusion.
Homography – It is defined as a projective transformation between two planes or a mapping between two planar projections of an image, describing the relative motion between two images when the camera or observed object moves. It can be mathematically represented in homogeneous coordinates and decomposed into affine and metric transformations.
Homojunction – It is a semiconductor interface formed between two differently doped regions (p-type and n-type) of the same crystalline material, characterized by identical bandgaps. Normally used in Si (silicon) and GaAs (gallium arsenide) diodes / solar cells, this junction relies on doping differences to create an electric field for charge carrier separation
Homoleptic metal carbonyls – These are coordination complexes containing only metal atoms and carbon mono-oxide (CO) ligands. Formed mainly by transition metals, e.g., Ni(CO)4, Fe(CO)5, and Cr(CO)6, they are characterized by their volatility, thermal stability, and role in purifying metals (like in the Mond process for nickel).
Homologous annealing temperature (Tha) – It is not a fixed, single value, but rather a normalized, dimensionless ratio used to define the absolute temperature (T) in Kelvin at which a material is annealed, expressed as a fraction of its absolute melting temperature (Tm) in Kelvin. It is formally defined as Tha = T/Tm.
Homologous pairs – These are spectral lines for different elements which respond in the same way to changes in excitation conditions. One line can be used as an interval standard line for the other.
Homologous temperature (Th) – It is a dimensionless ratio, calculated as the material’s current temperature (T) divided by its melting point Tm, both in Kelvin (Th = T/Tm). It defines a material’s state of atomic mobility and deformation behaviour (creep) relative to its melting point. A higher ‘Th’ (closer to 1) means faster diffusion, lower strength, and higher creep deformation.
Homology – It refers to a direct, one-to-one correspondence or structural similarity between a prototype and its model (or two distinct systems). Homologous components or points share similar positions, functions, or characteristics, allowing for analysis of deformation, stress, or design similarity across different scales or types of systems.
Homology groups – These are the factor groups formed by the quotient of the group of i-cycles by the subgroup of i-boundaries, which partition cycles into equivalence classes known as homology classes, with the dimension of these groups corresponding to the Betti numbers.
Homopolar generator – It is a generator in which current and magnetic field direction are constant as the machine rotor revolves.
Homopolar motor – It is a motor which produces torque from a current and magnetic field which does not change direction.
Homopolymer – It is a polymer derived from a single type of monomer, resulting in a chain with identical, repeating structural units. These are frequently produced through addition polymerization to create high-molecular-weight, structurally consistent materials, such as polypropylene, polyethylene, and poly-vinyl chloride (PVC).
Homo-polymerization – It is a process where a single type of monomer reacts with itself to form a long-chain macro-molecule (homopolymer) with uniform repeating units. It typically utilizes addition or step-growth techniques to produce polymers like polyethylene, polystyrene, or polyvinyl chloride. This method is important for engineering materials with specific, consistent properties.
Homoscedasticity – In regression analysis, it is the property that the conditional distributions of ‘Y’ for fixed values of the independent variable all have the same variance.
Honeycomb– It is the manufactured product of resin-impregnated sheet material (paper, glass fabric, and so on) or metal foil, formed into hexagonal-shaped cells. It is used as a core material in sandwich construction.
Honeycomb ceramic – It is a lightweight porous structure formed by extruding materials like cordierite, alumina, or silicon carbide into a rigid grid of numerous parallel, thin-walled, polygonal (typically hexagonal) channels. It provides high surface area-to-volume ratios, extreme thermal stability, and low pressure drop for applications in catalysis, filtration, and high-temperature insulation.
Honeycomb sandwich – It is a structural design consisting of two thin, strong, and stiff faces separated by a relatively thick and lightweight honeycomb core, which provides a high stiffness-to-mass ratio suitable for applications with weight limitations.
Honeycomb sandwich structure – It is a high-performance composite material consisting of a lightweight, cellular honeycomb core (typically hexagonal) bonded between two thin, rigid, high-strength face sheets. It acts as a structural panel designed to offer exceptionally high stiffness-to-mass and strength-to-weight ratios, with the core bearing shear loads and skins resisting bending and in-plane loads.
Honeycomb structures -These are structures which have the geometry of a honeycomb to allow the minimization of the quantity of used material to reach minimal weight and minimal material cost. The geometry of honeycomb structures can vary widely but the common feature of all such structures is an array of hollow cells formed between thin vertical walls. The cells are frequently columnar and hexagonal in shape. A honeycomb-shaped structure provides a material with minimal density and relatively high out-of-plane compression properties and out-of-plane shear properties.
Honing – It is a low-speed finishing process which is used mainly to produce uniform high dimensional accuracy and fine finish, most frequently on inside cylindrical surfaces. In honing, very thin layers of stock are removed by simultaneously rotating and reciprocating a bonded abrasive stone or stick which is pressed against the surface being honed with lighter force than is typical of grinding.
Honing machines – These are precision machine tools designed for finishing internal (and sometimes external) cylindrical surfaces by removing minimal material to correct size, shape (cylindricity, roundness), and surface roughness. They utilize rotating and reciprocating abrasive sticks to create a distinct, consistent crosshatch surface finish, important for oil retention and optimal lubrication in bearings, gears, and engine bores.
Honing tool – It is a machining tool used in the finishing process of honing, which refines the surface of a work-piece, typically an internal cylindrical surface like a bore. It consists of abrasive stones or sticks that remove small quantities of material to improve dimensional accuracy, surface finish, and roundness.
Honneff and Mecking model – It is frequently referred to as a ‘relaxed constraints’ (RC) model. It is a foundational theory in metal plasticity and crystal plasticity finite element modeling (CPFEM) used to predict texture evolution during large-strain plastic deformation. It addresses limitations in the traditional Taylor model by relaxing specific shear constraints in rolling, allowing for more realistic grain deformation and better agreement with experimental results for face-centered cubic (fcc) metals.
Hood – It is used to capture exhaust air / gas. It is the point where contaminated air / gas is drawn into the ventilation system. The sizes and shapes of hoods are designed for specific tasks or situations. The air / gas speed (velocity) at the hood opening and inside the hood is required to be enough to catch or capture and carry the air / gas contaminants. To be most effective, the hood is required to surround or enclose the source of contaminant or be placed as close to the source as possible.
Hood design – It involves designing the hinged, protective, and aerodynamic covering for a vehicle’s engine compartment. It focuses on balancing safety (pedestrian and occupant protection), structural integrity, NVH (noise, vibration, harshness) reduction, and manufacturability using materials like steel or aluminum.
Hood face – It normally refers to the open area or the plane of entry through which contaminated air, fumes, steam, or smoke enters an exhaust or ventilation device. This is a critical component in the design of ‘local exhaust ventilation’ (LEV) systems, such as laboratory fume hoods, or industrial exhaust hoods.
Hook – It is an abrupt deviation from straightness. Hook can be caused by non-uniform metal flow during break-through.
Hook block assembly – It is a vital component in a crane’s lifting mechanism. It consists of a hook, sheaves (pulleys), bearings, and a strong structural framework. This assembly is designed to manage the wire rope, distribute load weight evenly, and provide a secure point of attachment for lifting.
Hook conveyor – It is a material handling system which uses a continuous chain, cable, or belt equipped with specialized hooks, pendants, or hangers to transport products along a defined, frequently elevated, path. These conveyors are typically used to hang, suspend, or move items horizontally, vertically, or at inclines, frequently through processes like painting, cleaning, or assembly.
Hooker extrusion – It is a specialized, two-stage cold-forming process used mainly to produce small, thin-walled, seamless tubes (e.g., aluminum, copper, steel). It involves forcing a pre-formed cup-shaped blank through a die using a punch that acts as both a pusher and a mandrel, reducing both the outer diameter and wall thickness.
Hookean spring – It is an elastic component which follows Hooke’s law, meaning its restoring force (F) is directly proportional to its displacement (x) from equilibrium. It behaves linearly (F =kx), where ‘k’ is the constant stiffness. It returns to its original shape after loading, provided it stays within its elastic limit.
Hook, lifting – It is a device for grabbing and lifting loads by means of a device such as a hoist or crane. A lifting hook is normally equipped with a safety latch to prevent the disengagement of the lifting wire rope sling, chain or rope to which the load is attached.
Hooke’s law – It is a generalization applicable to all solid material, which states that stress is directly proportional to strain and is expressed as stress / strain = s/e = E, where ‘E’ is the modulus of elasticity or Young’s modulus. The constant relationship between stress and strain applies only below the proportional limit.
Hooke’s law of elasticity – It states that within the elastic limit of a material, the stress (load) applied is directly proportional to the strain (deformation) produced. It defines the linear elastic behaviour of metals where they return to their original shape upon unloading.
Hooke’s modulus – It is very frequently referred to as Young’s modulus or the modulus of elasticity (E). It is a fundamental material property which quantifies the stiffness of a solid material. It defines the linear relationship between stress (force per unit area) and strain (proportional deformation) within the material’s elastic range, as stated by Hooke’s law.
Hoop – It is the ply laid onto a mandrel at a 90-degree angle. It is mainly used in reference to filament winding of cylindrically shaped objects.
Hoopes process – It is an electrolytic refining process for aluminum, using three liquid layers in the reduction cell.
Hoop strain – It is also called circumferential strain. It is the deformation in the circumferential direction of a cylindrical or spherical shell under stress, defined as the change in circumference divided by the original circumference. It is a fundamental parameter for determining structural integrity and expansion in pressure vessels and pipes.
Hoop stress – It is a type of stress experienced by the walls of a circular or cylindrical object. It acts in a circumferential direction perpendicular to the axis of the structure. This stress phenomenon is especially significant in engineering applications involving pressurized vessels, pipes, and other cylindrical components, where it directly influences structural integrity and safety considerations. Hoop stress is a fundamental mechanical concept that plays a crucial role in understanding the behaviour of cylindrical structures under internal pressure. Hoop stress is the force which tries to split the cylinder in half along its length. This stress is crucial in engineering applications involving pressurized structures.
Hop cluster – It refers to a group of nodes organized around a central cluster head (CH), where communication between members and the cluster head occurs within a defined maximum number of hops (d-hops). These clusters facilitate efficient data routing, reduce energy consumption, and improve network scalability by restricting the communication range, frequently employing multi-hop paths to reach a base station.
Hopf bifurcation – It is a local, critical transition where a stable equilibrium point (steady state) loses stability as a parameter changes, causing the birth or death of a limit cycle (self-excited oscillation). It occurs when a complex conjugate pair of eigenvalues of the linearized system crosses the imaginary axis into the right half-plane.
Hopkinson bar – It is a one-dimensional waveguide, typically with a circular cross-section, used to generate and measure stress waves in materials under dynamic loading conditions, such as those produced by projectile impact or explosives. It facilitates the assessment of dynamic properties like stress-intensity factors through precise strain measurements.
Hopkinson pressure bar – It is frequently referred to as a ‘split-Hopkinson pressure bar’ (SHPB) or Kolsky bar. It is a specialized experimental apparatus used to characterize the dynamic mechanical properties of materials under high strain rates, typically ranging from 100 to 10,000 per second. It is necessary for understanding how metals and other materials behave during rapid deformation, such as in ballistic impacts, automotive crashes, or explosions.
Hopper cars – These are specialized railway freight cars designed for transporting bulk, loose commodities, such as coal, grain, ore, and cement, featuring slope-sheeted, funnel-shaped bottoms for rapid, gravity-assisted unloading through gates. Engineered with open or covered tops, they are optimized for structural integrity against vertical loads, longitudinal stress, and internal pressure during pneumatic discharge.
Hopper feeder – It is a device, typically comprising a container with converging, sloped walls, designed to store and uniformly dispense bulk materials (powders, granules, parts) into a processing machine. It regulates material flow using gravity and mechanical aids, such as vibrators or conveyors, to ensure continuous, metered, and controlled feeding.
Hopping bandwidth – It refers to the total spectrum range over which a carrier frequency shifts or ‘hops’ in a pseudo-random pattern to transmit signals, frequently used to improve security and avoid interference. It covers multiple narrowband channels, where the instantaneous bandwidth is just one channel, but the total hopping bandwidth is the entire operational span.
Hopping model – It is a mathematical or physical framework simulating the discrete, step-by-step transport of particles (electrons, charge carriers, or atoms) between localized sites on a lattice, rather than continuous flow. It is mainly used to analyze charge transport in amorphous semi-conductors, insulators, and for modeling robotic locomotion or stochastic transport in complex systems.
Hopping pattern – It is a predefined, synchronized sequence of frequency changes used in communication systems to switch carrier frequencies rapidly. It acts as a pseudo-random code (‘frequency-hopping spread spectrum’ FHSS) which spreads a signal over a wide bandwidth, reducing interference and improving security. The pattern includes a hopset of potential frequencies and a hop rate.
Horizontal asymptote (y = b) – It represents the limiting, long-term behaviour of a system’s output (y) as an independent variable (frequently time ‘t’ or input ‘x’) approaches positive or negative infinity. It indicates the steady-state value or horizontal trend line that a function approaches, signaling that the system’s output stabilizes or settles.
Horizontal axis – It is also called x-axis. It is the main, left-to-right reference line on a 2D Cartesian coordinate system, typically representing the independent variable (such as time, distance, or angle). It is parallel to the ground or base of a graph, frequently used to map independent data points.
Horizontal axis casting machine – It is a type of centrifugal casting machine used in foundries where a cylindrical mould (die) rotates around a horizontal axis at high speeds, typically 300 rpm (revolutions per minute) to 3,000 rpm, while molten metal is poured into it. The centrifugal force forces the molten metal against the inner wall of the mould, creating high-density, hollow, tubular, or cylindrical castings without the need for cores.
Horizontal axis wind turbines – These are wind energy converters featuring a rotor shaft and electrical generator positioned horizontally, parallel to the ground and wind flow, atop a tall tower. Engineered for high efficiency in large-scale power generation, they use aerodynamic blades (airfoils) which generate lift to spin the rotor.
Horizontal beam – It is a main structural element designed to span horizontally between supports (columns or walls), acting as a load-bearing member which resists bending, shear, and vertical loads from roofs or floors. These members convert vertical gravity loads into bending moments and shear forces, transferring them safely to vertical supports.
Horizontal beam width – It is also called azimuth beamwidth. It is the angular width in degrees (measured in the horizontal plane) of an antenna’s main radiation lobe, defined as the points where power density drops to half (-3 decibels, dB) of its maximum value. It determines how focused or wide the signal coverage is horizontally.
Horizontal batch furnace – It is a versatile batch-type furnace which can give light or deep case depths, and because the parts are not exposed to air, horizontal batch furnaces can give surfaces almost entirely free of oxides.
Horizontal bracing – It is a structural system installed in horizontal planes (floors or roofs) to stabilize a building by transferring lateral forces, such as wind, seismic activity, or crane loads, from the perimeter to the vertical bracing components. It acts as a rigid diaphragm, connecting vertical elements to improve overall structural stiffness.
Horizontal channel – It is an open channel with a bottom slope of zero, meaning the bed does not incline in any direction. These structures are designed for uniform flow control, liquid transport, or specialized tasks like hydraulic, geotechnical, or microfluidic applications, characterized by a constant depth profile.
Horizontal coefficient – It normally refers to dimensionless factors, like the horizontal seismic coefficient (Ah or kh) used in structural design to calculate lateral earthquake forces as a fraction of gravity. It represents ratios such as seismic load per unit mass, earth pressure, or thermal expansion.
Horizontal consolidation – It refers to the time-dependent reduction in volume of saturated soil, where water escapes radially towards vertical drains rather than just vertically. It is characterized by the horizontal coefficient of consolidation (ch), used to design soil improvement with prefabricated vertical drains (PVDs)
Horizontal conveyor – It is a conveyor system featuring a flat or low incline profile, needing periodic evaluations to ensure proper alignment and material flow for the maintenance of smooth operation.
Horizontal corner radius – It defines the curvature applied to a sharp 90-degree corner in a 2D plan view, horizontal, or ‘flat’ plane (such as a moulded part layout, sheet metal pattern, or road intersection). It serves to replace a sharp, stressed edge with a smooth curve (a radius) to improve structural integrity, reduce stress concentrations, or allow for material flow.
Horizontal corners – These are the corners which lie parallel to the forging plane or the parting line of the dies. These typically connect the web of a forging to a rib or boss. These extend horizontally, corresponding to the direction of metal flow during forging.
Horizontal curve – It is a curve in the alignment of a pipeline, conveyor, road or railway which changes the direction of the path in a horizontal plane. It is essentially a bend which allows for a gradual change in direction, rather than a sharp turn. These curves are used to connect two straight sections (tangents).
Horizontal directional drilling – It is a trenchless engineering method for installing underground pipes, cables, and conduits along a prescribed bore path using a surface-launched drilling rig. It minimizes surface disruption, making it ideal for crossing obstacles like rivers, roads, and railways. The three-stage process involves drilling a pilot hole, enlarging it through reaming, and pulling back the product pipe.
Horizontal divergence – It is the net outward flow of fluid (e.g., air, water) from a specific region, where more fluid leaves a horizontal area than enters it, resulting in a positive value. It indicates a source of flow, frequently driving subsidence (downward motion) or compensating for convergence.
Horizontal drains – These are small-diameter perforated pipes inserted into gently sloping holes drilled into soil or rock embankments to reduce groundwater pressure. They are a, primarily, geotechnical, method used to increase slope stability, prevent landslides, or stabilize active failures by lowering the water table and reducing pore-water pressure.
Horizontal drilling – It is a technique in oil, gas, and utility industries which involves drilling a wellbore which deviates from vertical to steer horizontally, typically at angles above 80-degree or parallel to a formation. It maximizes reservoir contact, increases production, and allows for trenchless, non-invasive installation of underground utilities.
Horizontal equilibrium – It is a state where the sum of all horizontal forces acting on a body is zero (Sigma Fx = 0), resulting in no horizontal acceleration. This indicates that applied horizontal forces are perfectly balanced by opposing forces like friction or structural resistance, maintaining a constant velocity or static position.
Horizontal extension – It refers to the lateral, horizontal, or non-vertical expansion of a structure, wellbore, or project, frequently defined by its length rather than its height or depth. It is a critical, constraint-driven concept focused on maximizing horizontal distance within specific geological, mechanical, or logistical limits.
Horizontal fillets – These are concave, rounded, interior corners that connect a web to an adjacent vertical projection, such as a rib or boss. They are termed ‘horizontal’ since they extend parallel to the forging plane, or the parting line, of the die. They are found at the junction between a web and a rib or between a wall and the bottom of a vertical cavity. They facilitate proper metal flow into die impressions, reduce stress concentration in the finished part, and prevent premature forging die breakage.
Horizontal fixed position pipe welding – It is the position of a pipe joint in which the axis of the pipe is approximately horizontal, and the pipe is not rotated during welding.
Horizontal floor space – It is the spatial requirement for housing and storing a conveyor system, demands consideration for efficient space utilization and accessibility.
Horizontal forging machines – These are specialized mechanical or hydraulic presses which operate with horizontal motion to shape metal stock, mainly through upsetting, piercing, and extrusion. These high-precision units utilize a horizontal ram and a two-part die system to forge, clamp, and form long rods or pipes at high speeds. These are forging presses which operate in a horizontal plane, frequently used to create complex shapes from bar or rod stock, such as bolts, gears, and fasteners.
Horizontal ground motion – It refers to the lateral, side-to-side vibrations of the earth’s surface caused by seismic waves during an earthquake. As a main component of seismic action, it is measured by sensors, typically in two orthogonal horizontal directions (frequently north-south and east-west), which are critical for structural, geotechnical, and earthquake-resistant design.
Horizontal intercept – It is normally known as the x-intercept. It is the point where a graph or function crosses or touches the horizontal axis (the x-axis). At this specific point, the output of the function, or the vertical coordinate (y-value), is zero. Horizontal intercept also refers to a point where a test line drawn across a polished, etched micrograph of a metal sample intersects a grain boundary. This is a key component of the mean linear intercept method (frequently used for determining average grain size).
Horizontal jet – It is a stream of fluid (liquid or gas) discharged from an orifice, nozzle, or pipe into a surrounding medium (ambient fluid) parallel to a horizontal plane, typically driven by momentum. In several practical cases, this jet is submerged in a fluid of similar density and can experience buoyancy forces which cause it to curve or rise over distance.
Horizontal loading – It refers to lateral forces applied parallel to the ground, perpendicular to a structure’s vertical axis. These, such as wind, seismic activity, earth pressure, and brake forces, create lateral displacement, shear, and overturning moments, necessitating resistance from shear walls, bracings, and diaphragms.
Horizontal mechanical presses – These are specialized machines which use a horizontally moving ram to forge metal stock (bars or tubes) by applying axial pressure, causing material to flow into die cavities. They utilize two gripper dies, one fixed, one moving, to hold the work-piece while a punch expands or shapes the heated end, normally producing parts like gears, bolts, and valves in high-speed, multi-pass operations.
Horizontal permeability (kh) – It is a measure of a porous medium’s ability to transmit fluids parallel to its bedding planes or depositional layers. It is perpendicular to the gravitational field and normally higher than vertical permeability (kv) because of the rock layering, playing an important role in fluid flow, reservoir simulation, and horizontal well productivity.
Horizontal pipeline – It is a conduit, frequently supported at intervals, designed to transport fluids or gases parallel to the ground or sea floor, needing careful analysis of sag, deflection, and stress because of the self-weight and content load. It is frequently associated with horizontal directional drilling (HDD) for underground installations or long-distance surface transport.
Horizontal platform – It refers to a foundational, shared technology layer, framework, or physical system designed to support multiple, diverse applications, products, or services across a wide range of industries or functional areas. Unlike vertical solutions which are customized for a single, specific purpose, a horizontal platform provides standardized capabilities which are reused across different, frequently unrelated, contexts to improve efficiency and reduce development costs.
Horizontal position fillet weld – It is the position in which welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface.
Horizontal position groove weld -It is the position of welding in which the weld axis lies in an approximately horizontal plane and the weld face lies in an approximately vertical plane.
Horizontal positioning – It is the precise determination or layout of an object’s location on a horizontal plane (x-y axis) relative to a reference datum or coordinate system. It ensures accuracy in surveying and construction, typically needing precision within +/- 15 centimeters, using tools like GPS (global positioning system), mapping, or control networks to align infrastructure accurately.
Horizontal ram – It refers to the reciprocating, horizontal-acting hydraulic or mechanical piston (or plunger) mechanism used on machinery to force metal through a die (extrusion) or push a tool through a work-piece (broaching / forging). It is the main component of a horizontal hydraulic extrusion press or a horizontal broaching machine.
Horizontal reaction – It is the horizontal force component generated at a structural support to resist lateral loads or prevent horizontal movement of a member. It acts along the horizontal axis, balancing horizontal loads or components from inclined forces, and is important for equilibrium in pinned, hinged, or fixed supports.
Horizontal reactor – It is a vessel oriented horizontally, designed for chemical reactions involving high-viscosity materials, solid-liquid mixing, or processes needing low pressure drop at high flow rates. Unlike vertical reactors, these are frequently partially filled, utilizing robust agitators (e.g., paddle, anchor, or screw) to ensure efficient mixing and self-cleaning of walls.
Horizontal rolled position pipe welding – It is the position of a pipe joint in which the axis of the pipe is approximately horizontal, and welding is performed in the flat position by rotating the pipe.
Horizontal return tubular (HRT) boiler – A horizontal return tubular boiler is a fire-tube boiler normally supported in a brick combustion chamber. The hot gases from combustion sweep along the underside of the shell then return through the fire tubes to the chimney connection.
Horizontal separator – It is a cylindrical pressure vessel oriented parallel to the ground, designed to separate oil, gas, and water from production streams using gravity, velocity changes, and impingement. Engineered for high liquid-to-gas ratios and large-volume surges, horizontal separators allow better separation of foamy liquids and efficient liquid-liquid settling.
Horizontal split dies – These are specialized tooling, typically consisting of two or more distinct, separable parts which meet along a horizontal parting line. They are used to shape, forge, or cast metal components, particularly complex or long, horizontally oriented parts, by closing together around a work-piece and separating to allow for easy extraction.
Horizontal stand – It is a type of roll stand where both work rolls are oriented horizontally, meaning they rotate on a horizontal axis. This contrasts with vertical stands, where the rolls are positioned vertically. Horizontal stands are a fundamental component of several rolling mills, frequently working in conjunction with vertical stands to achieve desired metal shaping and thickness reduction. Horizontal stand has both the rolls horizontally mounted. It comprises of a roll stand, mill spindles, a pinion stand, a gear reducer and a motor. In the case of a regular pass line, the roll stand slides on the exterior of the sole plate.
Horizontal stiffness – It is the ability of a structure or component to resist deformation, such as bending or shearing, when subjected to lateral (horizontal) loads. It is quantified as the ratio of applied horizontal force (F) to the resulting horizontal displacement (d), expressed as K = F/d. Higher stiffness implies less deflection under load.
Horizontal Sync – It is a signal which triggers the start of each horizontal scan line on a display (cathode ray tube, CRT or liquid-crystal display, LCD), ensuring pixels are placed at the correct position to prevent image distortion, tearing, or misalignment. It acts as a timing pulse between the end of one line and the beginning of the next.
Horizontal tank – It is a cylindrical, pressure-rated, or atmospheric container oriented with its longitudinal axis parallel to the ground, designed for storing liquids or gases. Normally used for fuel, water, and chemical storage, they are favoured for limited-height applications, offering high stability, ease of transport, and, frequently, double-skin configurations for hazardous material containment.
Horizontal tube – It refers to a cylindrical, hollow conduit or vessel oriented parallel to the ground, designed for the transport of fluids (liquids / gases), structural applications, or heat transfer.
Horizontal velocity – It is the component of an object’s velocity parallel to the ground (x-axis), representing the rate of change in horizontal position over time. It is normally assumed to be constant in projectile motion because of the absence of horizontal forces. It is calculated as Vx = Vo x cos A.
Horizontal velocity field – It involves analyzing and designing the spatial distribution of horizontal fluid velocities or tectonic motions to optimize systems such as airflow, aquatic currents, or structural deformation studies. Techniques include computational modeling, particle image velocimetry (PIV), and geostrophic flow adjustment to manage vorticity, heat transfer, or to predict stress in, for example, geological structures or stirred vessels.
Horizontal vessel – It is a cylindrical container oriented with its long axis parallel to the ground, designed to store, separate, or process liquids and gases. Typically supported by two or more saddles, these vessels feature dished ends, handle larger volumes, and are normally used as pressure accumulators or separators in industrial plants.
Horizontal vibration – It is the back-and-forth oscillation of a structure or machine component parallel to the ground or perpendicular to its vertical axis (lateral / transverse movement). It represents a specific direction of mechanical movement, frequently caused by dynamic loads, friction, or unbalanced forces, typically measured to analyze structural integrity and serviceability.
Horizontal welding – It is an out-of-position technique where the weld axis lies in a horizontal plane, normally used in structural steelwork and pipeline fabrication. The welding torch is normally oriented horizontally, with 2F (fillet) or 2G (groove) classifications used when the joint is on a vertical surface.
Horizontal well technology – It is a directional drilling method that deviates a wellbore from vertical to a near-horizontal angle (above or equal to 80-degree) within a target reservoir. By increasing the contact area between the wellbore and the rock formation, it improves oil and gas production, reduces water coning, and maximizes recovery in both conventional and unconventional, low-permeability, or fractured, reservoirs.
Horizontal wind – It refers to the movement of air parallel to the earth’s surface, driven by pressure differences (pressure gradient force), friction, and the Coriolis force. It is measured by anemometers and acts as the primary power source for conventional horizontal-axis wind turbines (HAWTs), which feature rotors mounted parallel to the ground.
Horn – In a resistance welding machine, it is a cylindrical arm or beam which transmits the electrode pressure and normally conducts the welding current. It is also a cone-shaped member which transmits ultrasonic energy from a transducer to a welding or machining tool.
Horn antenna – It is a type of antenna that typically features a flared structure, allowing it to provide useful gain over a decade bandwidth, with designs such as the short axial-length, double-ridged horn achieving a gain of 10 dB (decibel) over a frequency band of 0.2 giga-hertz to 2 giga-hertz. It is frequently used in ‘frequency modulated continuous wave’ (FMCW) systems for applications like surface-penetrating radar.
Horner plot – It is defined as a graphical representation which uses the log of Horner time on the x-axis and bottom-hole pressure on the y-axis to analyze reservoir characteristics, including pore pressure and permeability, by extrapolating a straight line to the y-intercept. Horner plot is a semi-log graph used in petroleum engineering to analyze pressure buildup data, plotting shut-in bottom-hole pressure (Pws) against the logarithm of normalized time, log[(tp – dt)/dt]. It determines reservoir permeability, skin factor, and initial reservoir pressure (P*) by extrapolating the linear trend, representing equilibrium.
Hornfels – It is a fine-grained contact metamorphic rock.
Horn gate – It is also called horn sprue. It is a type of bottom-gating system used in foundry casting, specifically designed with a curved, tapered, horn-like shape to feed molten metal into the lowest part of a mould cavity. It is typically used for pouring circular or thin, flat castings to ensure quiet, upward filling.
Horn press – It is a mechanical metal forming press which is equipped with or arranged for a cantilever block or horn which acts as the die or support for the die. It is used in forming, piercing, setting down, or riveting hollow cylinders and odd-shaped work.
Horn spacing – It is the distance between adjacent surfaces of the horns of a resistance welding machine.
Horse – It is a mass of waste rock lying within a vein or ore-body.
Horsepower (hp) – It is a unit of measurement of power, or the rate at which work is done, normally in reference to the output of engines or motors. There are several different standards and types of horsepower. Two common definitions used today are the imperial horsepower as in ‘hp’ or ‘bhp’ (brake horse power) which is around 745.7 watts, and the metric horsepower as in ‘cv’ (cavallo vapore, or cavalo-vapor) or ‘PS’ (PferdStarke) which is around 735.5 watts.
Horseshoe thrust bearing – It is a tilting-pad thrust bearing in which the top pads are omitted, making an incomplete annulus.
Horseshoe vortex – It is a U-shaped fluid flow structure consisting of a bound vortex (parallel to a surface) connected to two trailing (tip) vortices. It forms when a boundary layer interacts with an adverse pressure gradient (e.g., around a wing or base of a cylinder), creating substantial aerodynamic lift, drag, and flow-induced scour.
Horst – It is an upfaulted block of rock.
Hose – It is also called a hose-pipe. It is a flexible hollow tube or pipe designed to carry fluids from one location to another, often from a faucet or hydrant. Modern hoses are made of rubber, canvas, and helically wound wire. Hoses can also be made from plastics such as poly-vinyl chloride and poly-tetra-fluoro-ethylene. Materials such as stainless steel and poly-ethylene terephthalate are used for hoses capable of carrying low-temperature liquids such as liquid oxygen and liquid nitrogen.
Hoshin Kanri – It is frequently called policy deployment. It is a structured, ‘lean’ strategic planning methodology which aligns an organization’s high-level strategic goals with daily operations, ensuring every employee works toward common, measurable objectives. Originating from Japanese ‘direction management’ (compass needle), it breaks down long-term visions into annual, actionable targets, using techniques like the X-matrix for alignment.
Host – It is a network-connected device (physical server, virtual machine, or container) which provides resources, storage, and services to other users or devices. It acts as a central hub for data processing, management, and communication, utilizing IP (internet protocol) addresses to facilitate the transfer of data.
Host device – It is a main computer, system, or networked hardware which provides resources, data, or services to connected peripheral devices, clients, or subordinate components. It acts as a central hub in a network, controlling communication and managing peripherals, frequently identified by a unique IP (internet protocol) address.
Host grid – It refers to the main, existing electrical power network (distribution or transmission) to which different components, such as distributed generation, renewable energy sources, or direct current (DC) microgrids, are connected. It acts as the infrastructure receiving power, allowing for energy exchange, management, and stability.
Host-guest chemistry – It focuses on the non-covalent binding of a small ‘guest’ molecule within the cavity of a larger ‘host’ molecule. Engineered for molecular recognition, it uses weak forces like hydrogen bonding and van der Waals forces to create selective, stable complexes for sensors, and materials science.
Hostile environment – It is also called harsh environment. It is a setting which exposes materials, components, or systems to extreme conditions, such as high temperature, pressure, corrosion, radiation, or mechanical shock, which threaten their structural integrity, performance, and survival. These conditions typically exceed the standard operating range of equipment, demanding specialized materials and design.
Host lattice – It is a rigid, often crystalline material structure (e.g., in phosphors) or a meso-level CAD (computer aided design) design (in additive manufacturing) which provides a framework for accommodating functional guest materials. In materials engineering, it stabilizes dopant ions to improve luminescence. In structural engineering, it defines the 3D periodic arrangement for strength, weight reduction, and energy absorption.
Host machine – It is the main, physical hardware platform (computer, server, or work-station) which provides resources, such as CPU (central processing unit), memory, and network access, to support other entities like virtual machines, containers, or peripheral devices. It serves as the development, compilation, or execution environment for software or systems intended for a separate target machine.
Host medium – It refers to the main material, system, or environment which supports, houses, or enables the operation of another, frequently smaller or embedded, component. The specific definition varies depending on whether it is applied to material science, tele-communications, or computing contexts.
Host rock – It refers to the native geological formation which surrounds, encloses, or contains a mineral deposit, ore body, or engineered structure (such as a tunnel or nuclear waste repository). It defines the physical, thermal, and chemical environment, directly influencing stability, excavation design, and groundwater flow.
Host signal – It is a main data signal, such as an image, audio file, video, or data stream, which is used as a carrier to hide or embed another signal (secret message or watermark). This technique is fundamental to data hiding and steganography, where the goal is to transmit information without altering the perceptibility or quality of the original host content.
Host structure – It is a supporting, frequently porous framework (e.g., crystal lattices, molecular cages, or solid surfaces) which binds, houses, or supports ‘guest’ species (molecules, ions, or devices). This structure dictates the shape, size, and location of the guest species, enabling applications like catalysis, sensing, and material storage.
Host system – It is a foundational machine, physical, virtual, or cloud-based, which provides resources, services, or networking capabilities to other connected devices (clients), applications, or virtual machines. It acts as a central hub, managing hardware resources like CPU (central processing unit), memory, and storage to facilitate data processing and communication.
Hot annealing and pickling line – This line represents a continuous production process used in steel manufacturing, specifically for treating hot-rolled stainless-steel strip. It combines annealing (heat treatment) and pickling (chemical removal of surface oxides) to achieve a desired metallurgical structure and surface finish. This line prepares the steel for further cold rolling or other downstream processes.
Hot band – It is a coil of steel rolled on a hot-strip mill. It is also called hot rolled coil. It can be sold in this form to customers or further processed into other finished products.
Hot band starting texture – It refers to the initial, inherited crystallographic orientation distribution of grains in a hot-rolled metal strip (or band) before it undergoes cold rolling and subsequent annealing. This texture is formed during the high-temperature deformation (hot rolling) and subsequent cooling / coiling, considerably influencing the material’s anisotropy, formability, and final recrystallization texture.
Hot band textures – These refer to the specific, non-random orientation distribution of crystal grains (crystallographic texture) which develop in metal strips during the hot rolling process. This initial texture is important since it influences the microstructure, recrystallization behaviour, and final, desired texture after downstream processing like cold rolling and annealing.
Hot bending – It is a process which shapes metal pipes, tubes, or bars by heating them to high temperatures (typically 850 deg C to 1,000 deg C), reducing yield strength and increasing ductility to allow for precise bending. Frequently using induction heating to apply heat in a narrow, controlled band, this method enables tighter radii and complex, high-strength shapes without fracturing or significant spring-back.
Hot blast air – It is the air which is heated in the hot blast stoves and fed to the BF through the tuyeres for the combustion of the fuel.
Hot blast main – It is the refractory lined pipe which connects the hot blast stoves with the bustle pipe.
Hot blast stove – Hot blast stove is used to preheat blast air used in the blast furnace for the combustion of fuel. It works as a counter-current regenerative heat exchanger. It consists of tall, cylindrical steel structures lined with different kinds of refractories and almost completely filled with checker bricks where heat is stored and then transferred to the fresh air to heat it to a specified temperature.
Hot blast temperature, blast furnace – Hot blast temperature improves the fuel efficiency of the blast furnace and allows higher furnace temperatures, which increases the capacity of furnaces. High hot blast temperatures are essential for efficient blast furnace operation since they reduce the furnace coke requirement substantially and facilitate the injection of auxiliary fuels such as pulverized coal as a replacement of blast furnace coke. The total energy savings possible by a combination of techniques is of the order of 0.12 million kilo calories per ton of hot metal. It results into lower operating costs because coke ratio reduces by 2.8 % per 100 deg C rise in blast temperature when it is maintained between 1,000 deg C to 1,200 deg C. Many modern furnaces operate at a hot blast temperature which is higher than 1,300 deg C.
Hot blast valve – It is a critical equipment for the operation of the blast furnace. This valve is intended for complete separation of a hot blast stove from a hot blast main under ‘on-gas’ operation of the stove. This valve is also effectively being used as a shut-off valve and back drafting valve. This valve when used for separation of a gas burner from the hot blast stove under ‘on-blast’ operation of the stove is known as burner valve or gas shut off valve. Hot blast valve is installed vertically in a pipeline. Hot blast valves are normally installed in the horizontal hot blast main near the stove. The pipeline is opened and closed by the movement of the valve disk with the use of electro-mechanical drive. In the event of power failure, it is possible to operate the drive manually. Hot blast valve normally consists of a water-cooled disc resting on a water-cooled seat, and moving vertically within a water-cooled valve body and bonnet, and other supporting members and mechanisms which maintains a smooth, exact seating and non-stick release of the disc.
Hot box process – In foundry practice, it is a resin-base (furan or phenolic) binder process for moulding sands which is similar to shell core-making. Cores produced with it are solid unless mandrelled out. It is the method of making and curing cores within a heated core-box. To form and cure the core, the core-box is heated to around 260 deg C. The sand used in this process contains a catalyst which hardens the binders in the core upon contact with the hot core-box. Complete curing while the core is still in the box results from the residual heat in the core, eliminating the need for conventional dryers or ovens. Frequently, cores created with the hot box process are shell cores.
Hot briquetted iron (HBI) – It is a compacted form of direct reduced iron which is manufactured with well-defined, consistent chemical and physical characteristics. It is produced by reducing iron oxide lumps, pellets, or fines, and compressing the material at a temperature of at least 650 deg C to achieve an apparent density of at least 5,000 kilograms per cubic meter. It is 100 times more resistant to reoxidation than conventional direct reduced iron and picks up 75 % less water. It also generates lesser fines, which provides higher value to users and reduces safety concerns during handling and shipping.
Hot carbonate process – It is also called hot potassium carbonate process or the hot pot process. It is a mature, energy-efficient method for removing high-concentration carbon di-oxide (CO2) and hydrogen sulphide (H2S) from gas streams (natural gas, syngas). It uses a hot (around 110 deg C to 120 deg C) aqueous potassium carbonate (K2CO3) solution (25 % to 35 %) to absorb acid gases, which are then stripped by reducing pressure rather than intense heating.
Hot carrier injection – It is a phenomenon in semi-conductors where electrons or holes gain high kinetic energy from intense electric fields, frequently near the drain of short-channel MOSFETs (metal oxide semi-conductor field effect transistor), allowing them to breach the silicon-oxide barrier and trap in the gate dielectric, leading to device degradation, increased threshold voltage, and instability.
Hot cathode – It is also called thermionic cathode. It is an electrode in a vacuum or gas-filled tube which emits electrons through thermionic emission when heated to high temperatures. Typically, a tungsten filament or coated metal is heated, enabling electrons to overcome the material’s work function. It is used in vacuum tubes, X-ray machines, and cathode ray tubes (CRTs). Hot cathodes typically achieve much higher power density than cold cathodes, emitting considerably more electrons from the same surface area.
Hot cathode gun – It is an electron gun which derives its electrons from a heated filament, which can also serve as the cathode.
Hot chamber machine – It is a die casting machine in which the metal chamber under pressure is immersed in the molten metal in a furnace. The chamber is sometimes called a gooseneck, and the machine is sometimes called a gooseneck machine.
Hot-cold working – It is a high-temperature thermomechanical treatment consisting of deforming a metal above its transformation temperature and cooling fast enough to preserve some or all of the deformed structure. It is also a general term which is synonymous with warm working.
Hot consolidation – It is a powder metallurgy process which simultaneously applies high temperature and mechanical pressure to loose metal powders or pre-compacted powder preforms to achieve full density (near-theoretical density). It combines the densification of pressing and the atomic bonding of sintering into a single step, reducing the pressure needed for consolidation and allowing for the production of high-performance, complex near-net-shape components.
Hot consolidation methods – These methods are applied to get fully dense metal powder compacts with controlled microstructures. This encompasses several diverse operations, including uniaxial hot pressing and pressure sintering, hot iso-static pressing, hot extrusion and hot forging.
Hot corrosion – It is an accelerated corrosion of metal surfaces which results from the combined effect of oxidation and reactions with sulphur compounds and other contaminants, such as chlorides, to form a molten salt on a metal surface which fluxes, destroys, or disrupts the normal protective oxide.
Hot crack – It is a manufacturing defect occurring during the final stages of solidification in welding or casting, where tensile shrinkage stresses pull apart weak, brittle grain boundaries containing low-melting liquid films. Known as ‘solidification cracking’ or ‘hot tearing’, these cracks form at high temperatures (above 1,200 deg C) as the metal solidifies.
Hot cracking – It is also called solidification cracking. Hot cracking of weldments is caused by the segregation at grain boundaries of low-melting constituents in the weld metal. This can result in grain-boundary tearing under thermal contraction stresses. Hot cracking can be minimized by the use of low impurity welding materials and proper joint design.
Hot cracks – These are the cracks which develop in a weldment or casting during solidification. These cracks include several types of cracks which occur at high temperatures in the weld metal or heat affected zone. In general, hot cracks are normally associated with steels having high sulphur content. The common types of hot cracks include solidification cracks and liquidation cracks.
Hot cutoff saws – These are specialized industrial cutting machines designed to sever metal work-pieces (such as billets, blooms, bars, and rails) while they are still at high temperatures (typically 900 deg C to 950 deg C), normally immediately after emerging from a rolling mill or continuous casting machine. These saws operate using high-speed, hardened steel discs or friction blades which cut through red-hot steel by exceeding the tensile strength of the metal at the cutting point.
Hot deformation – It is also called hot distortion. It refers to the dimensional changes, bending, or plastic deformation which a sand mould or core undergoes when subjected to high temperatures during the pouring and solidification of molten metal. It is a important thermomechanical property which measures how the sand mixture reacts to heat-induced stresses and expansion, which can lead to casting defects like veining, scabs, or mould wall movement.
Hot deformation, sand sample – It is the change of form of a sand sample which accompanies the determination of hot strength.
Hot-die forging – It is a hot forging process in which both the dies and the forging stock are heated. Typical die temperatures are 110 deg C to 225 deg C which are lower than the temperature of the stock.
Hot die pressing – It is a powder metallurgy process which simultaneously applies high heat and uniaxial pressure to metallic or ceramic powders within a die, normally made of graphite, to achieve near-theoretical density. It combines compaction and sintering into one step, utilizing plastic deformation, creep, and diffusion to produce fully dense, high-performance, and low-porosity materials.
Hot-die trimming – It is a finishing process used to remove excess metal (flash) from a work-piece immediately after it has been formed through hot forging or hot stamping, while the material is still at a high temperature.
Hot dip – It consists of covering a surface by dipping the surface to be coated into a molten bath of the coating material.
Hot dip coating – It is a metallic coating got by dipping the substrate into a molten metal.
Hot dip galvanizing – It is a process in which an adherent, protective coating of zinc and iron-zinc alloys is developed on the surfaces of iron and steel products by immersing them in a bath of molten zinc. Majority of zinc coated steel is processed by hot dip galvanizing. One method of hot dip galvanizing is the batch process, which is used for fabricated steel items such as structures or pipes. This method involves cleaning the steel articles, applying a flux to the surfaces, and immersing them in a molten bath of zinc for different time periods to develop a thick alloyed zinc coating. The most common form of hot dip galvanizing for steel sheet is done on a continuous galvanizing line. Coiled sheet is fed from pay-off reels through flatteners. It is then cleaned, bright annealed, and passed through the coating bath. After leaving the coating bath, the coating thickness is controlled by an air knife or steel rolls. The sheet is then cooled and recoiled or cut into lengths. The hot dip process normally coats both sides of the sheet.
Hot direct reduced iron (HDRI) – It is produced in the vertical shaft kiln. It can be transported to an adjacent electric arc furnace at a temperature up to 650 deg C to take advantage of the sensible heat, which allows increase productivity during the steelmaking and reduction in the production cost. There are four alternatives which are being commercially available for the transport of hot direct reduced iron. These are (i) transport in a hot transport vessel, (ii) gravity transport of hot direct reduced iron, (iii) pneumatic transport of hot direct reduced iron, and (iv) hot transport conveyor system. Each of these alternatives has its best application, depending on such factors as transport distance, component arrangement, and conveying capacities.
Hot dry rock – It refers to deep, low-permeability, high-temperature (above 150 deg C to 200 deg C) geologic formations, typically igneous or metamorphic rock, which contain minimal or no water. Engineering these systems needs artificial fracturing (e.g., hydraulic stimulation) to create a heat exchanger, transforming them into ‘enhanced geothermal systems’ (EGS) to extract thermal energy.
Hot dry rock systems – These are geothermal resources, frequently categorized as ‘enhanced geothermal systems’ (EGS), which extract thermal energy from hot, low-permeability, and dry crystalline rock deep in the earth’s crust. Engineering involves creating artificial, fractured reservoirs by injecting high-pressure water, allowing circulating fluid to absorb heat for electricity or heating. Hot dry rock systems tap into massive, high-temperature (frequently above 150 deg C to 180 deg C) rock formations which lack natural fluids or permeability.
Hot electrons – These are non-equilibrium charge carriers with kinetic energy considerably higher than the surrounding lattice temperature, typically 1 electron volt to 4 electron volts, generated in materials through photon absorption (localized surface plasmon resonance, LSPR) or high-field acceleration ((metal oxide semi-conductor field effect transistors, MOSFETs). These high-energy particles are utilized to overcome energy barriers in catalysis or cause detrimental effects in semiconductor devices through, for example, hot-carrier injection.
Hot etching – In metallography, it is the development and stabilization of the micro-structure at high temperature in etchants or gases.
Hot extrusion – It is a process whereby a heated billet is forced to flow through a shaped die opening. The temperature at which extrusion is performed depends on the material being extruded. Hot extrusion is used to produce long, straight metal products of constant cross section, such as bars, solid and hollow sections, tubes, wires, and strips, from materials which cannot be formed by cold extrusion.
Hot extrusion dies – These are specially designed, hardened tool steel components which define the final cross-sectional profile of a material, which is forced through an orifice at high pressures and high temperatures (above the recrystallization temperature). These are the functional heart of the hot extrusion process, designed to withstand extreme thermal, compressive, and frictional stresses while shaping alloys like aluminum, steel, and copper.
Hot film anemometer – This method uses the flow rate dependent heat transfer from a heated body to the measuring medium. In the fields which are relevant for process engineering, this flow rate dependent cooling is not a function of the pressure and temperature, but of the type and number of particles which get into contact with the hot surface. This means the method determines the mass flow rate of the measuring medium directly. The sensor unit consists of two measurement resistors that are part of an electrical bridge circuit. One of these resistors assumes the temperature of the flowing gas, whereas the other resistor is electrically heated and, at the same time, cooled by the gas mass flow. A control circuit applies heat to the resistor so that a constant temperature difference exists between the resistors. The power is, hence, a measure of the gas mass flow rate. This provides the measured value directly in the units namely kilograms per hour or standard cubic metre per hour. The density correction of the measured value otherwise required is no longer necessary. The compact design of the sensor unit assures a minimum pressure drop of typically 0.1 kilopascal. For thin film sensors the response time is in the milliseconds range. Vibration insensitivity and an extremely wide span at accuracies up to 1 % of rate are the rule for all thermal mass flow meters.
Hot film anemometry – It is a thermal fluid velocity measurement technique which uses a thin, electrically conductive film deposited on a substrate (frequently quartz) to detect local flow speed based on heat transfer principles. As fluid flows over the electrically heated sensor, it cools, changing the film’s resistance.
Hot film sensors – These are robust, high-frequency transducers used for measuring flow velocity, turbulence, and shear stress by analyzing the convective heat loss from a heated, thin platinum or nickel film. They function by maintaining a constant temperature or power, with necessary current fluctuations indicating flow changes, making them necessary for automotive mass air flow (MAF).
Hot fluid – It is primary / thermal fluid. It is a liquid or gas designed to transport, store, or transfer thermal energy within a system, typically operating at elevated temperatures (up to around 300 deg C) to drive processes like heating, melting, or energy conversion. It acts as a heat transfer medium in exchangers.
Hot forge rolling – It is frequently referred to as roll forging or cross-wedge rolling. It is a specialized metal-working process which reduces the cross-sectional area of heated metal bars or billets by passing them between two contrary rotating roll segments. It is a hot-working process performed above the metal’s recrystallization temperature, frequently used to shape, thin, or elongate materials before final forging. It is a discrete forging technique rather than a continuous rolling process, producing high-strength, near-net-shape components.
Hot forging – Hot forging is the most widely used forging process. In hot forging process, forging is carried out at a temperature above the recrystallization temperature of the metal which means at the temperature at which the new grains are formed in the metal. This kind of extreme heat is necessary in avoiding strain hardening of the metal during deformation. Hot forging is a forging process in which the die and / or forging stock are heated. It is also the plastic deformation of a pressed and / or sintered powder compact in at least two directions at temperatures above the recrystallization temperature.
Hot forming – Hot forming is a metalworking process where metal is formed at high temperatures, typically above its recrystallization temperature, to achieve desired shapes and properties. This process involves heating the metal to increase its ductility, making it easier to form, followed by rapid cooling (quenching) to achieve high strength and hardness. The metal blank (sheet, bar, etc.) is heated in a furnace or induction heating system to a temperature above its recrystallization temperature (around 40 % to 60 % of its melting temperature). For steel, this temperature is typically around 900 deg C. The heated blank is then transferred to a press and formed into the desired shape using a die or tooling. The formed part is quickly cooled, often by quenching in the die or with a cooling system, to rapidly transform the microstructure and increase strength. The final part may undergo trimming, laser cutting, or other finishing processes. Hot forming is the plastic deformation of metal.
Hot-forming capacity – It refers to the capability of a metal or alloy to undergo severe, permanent plastic deformation at temperatures above its recrystallization temperature without fracturing or cracking.
Hot gas cleaning – It is a process which removes contaminants, specifically particulates, tars, and gaseous impurities like hydrogen sulphide (H2S), hydrochloric acid (HCl), and alkali compounds, from hot gas streams (typically above 260 deg C) directly after generation. It enables efficient, high-temperature utilization of syngas in turbines or fuel cells while preventing corrosion and erosion in downstream equipment.
Hot gas filter – It is a device designed to remove solid particulate matter from industrial gas streams at high temperatures, typically exceeding 260 deg C. Utilizing rigid ceramic, metal, or sintered metal fibre media, these filters protect downstream equipment from erosion, corrosion, and pollution, frequently achieving efficiencies exceeding 99 % (sub-micron level).
Hot gas filtration – It is a reliable high-temperature particulate separation technology used to efficiently separate particles from gases at high temperatures, utilizing rigid ceramic or metal filter elements. This process can achieve clean gas concentrations below 1 milligram per cubic meter. and protects downstream equipment (e.g., turbines, heat exchangers) from erosion and pollution, achieving above 99.9 % efficiency while preventing condensate blockage.
Hot geo-fluid – It is a naturally occurring, pressurized, hot water or vapour (steam) extracted from underground geological formations, frequently containing dissolved materials (brine) and gases. It acts as the carrier medium for extracting thermal energy from a geothermal reservoir to the surface for utilization in electricity generation, heating, or industrial processes.
Hot hardness – It is the ability of a material, such as tool steel or alloys, to maintain its hardness, strength, and resistance to plastic deformation at high temperatures (typically higher than 650 deg C). It is also known as red hardness. This property is important for cutting tools and high-temperature machinery to prevent wear and deformation.
Hot heading – it is a metal-working process used to create, enlarge, or shape the head of a fastener or component by applying pressure to the metal while it is heated above its recrystallization temperature. This process is mainly used for manufacturing high-strength, complex, or large-diameter fasteners and components.
Hot heel operation – In hot heel operation around 15 % to 20 % of metal and certain amount of slag are left at the furnace bottom after each tapping. The rest of the slag is removed from the furnace over the sill. This assists in the melting of fresh solid feed entering the furnace and allows practically a slag free tapping. Hot heel operation results into savings of the ferro- alloys and into energy efficiency.
Hot hole injection – It is a semiconductor phenomenon where high-energy (‘ho’) holes, generated by intense electric fields or plasmonic excitation, gain enough kinetic energy to surmount the potential barrier (typically around .6 electron volts for silicon-silicon di-oxide (Si-SiO2) and inject into the oxide dielectric or a nearby semiconductor, causing device degradation or enabling photo-detector functionality.
Hot hydrostatic extrusion – It is a specialized metal-forming process where a heated billet is extruded through a die using a pressurized, hot-stable fluid medium (e.g., glass or grease) rather than a mechanical ram. This technique eliminates container-wall friction, allows for high reduction ratios, and improves material flow, particularly at temperatures exceeding 700 deg C.
Hot impression-die forging – It is also called closed-die forging. It is a process where heated metal is deformed between two or more custom-shaped dies to create complex, high-strength parts. The work-piece is heated above its recrystallization temperature to improve ductility and reduce force requirements, filling die cavities to achieve precise geometries with minimal machining.
Hot indirect extrusion – It is a high-temperature metal forming process where a heated billet is placed in a container, and a die, mounted on a hollow ram, moves to force the material backward through the die orifice. The billet remains stationary relative to the container, eliminating friction.
Hot in-place recycling – It is an on-site, sustainable pavement rehabilitation process which restores deteriorated asphalt surfaces (typically top 20 millimeters t0 65 millimeters by heating, scarifying, mixing with binding agents / new materials, and re-compacting in a single continuous operation. It reduces costs by 30 % to 70 % and minimizes new material usage
Hot isostatic pressing – It is a manufacturing process, which is used to reduce the porosity of metals and increase the density of several ceramic materials. This improves the mechanical properties and workability of the material. The process can be used to produce waste form classes. It is also a process for simultaneously heating and forming a compact in which the powder is contained in a sealed flexible sheet metal or glass enclosure and the so-contained powder is subjected to equal pressure from all directions at a temperature high enough to permit plastic deformation and sintering to take place. Hot isostatic pressing is also a process which subjects a component (casting, or powder forgings etc.) to both high temperature and isostatic gas pressure in an autoclave. The most widely used pressurizing gas is argon. When castings are hot isostatically pressed, the simultaneous application of heat and pressure virtually eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion.
Hot junction – It is the sensing tip of a thermocouple where two dissimilar metal wires are welded or joined together to measure temperature. It generates a voltage (through the Seebeck effect) proportional to the temperature difference between it and a reference (cold) junction.
Hot line pickup – It consists of small particles of metal and metal oxide generated in the roll bite, which subsequently transfer to the rolled product. It can be distributed uniformly and / or in streaks.
Hot lines – It normally refers to energized electrical conductors, specialized maintenance techniques, or specific industrial testing processes. In case of electrical engineering, a hot line, is a live line / phase line. It is an electrical wire in a distribution or transmission system which has a non-zero voltage relative to the earth or ground. In case of maintenance, hot line work means live-line working and refers to the maintenance of electrical equipment, such as transmission lines, transformers, or insulators, while the equipment is energized (powered on). In case of automotive / production engineering, hot lines refer to highly specialized test cells used in automotive engine production to check that an engine is complete and operates correctly within a minimal process time, typically involving a highly automated procedure for testing and fault identification. In case of thermal engineering, the hot-wire method is a technique used to measure the thermal conductivity and thermal diffusivity of materials.
HOTLINK system – This process uses primarily gravity transport. HOTLINK system is the direct link combination between a hot discharge gas-based direct reduction vertical shaft furnace and a conventional electric arc furnace. It is a system which directly couples the hot discharge of the shaft furnace into the electric arc furnace by gravity. HOTLINK system supply hot direct reduced iron to the adjacent electric arc furnace at temperatures which are up to 700 deg C, by positioning the shaft furnace just outside and above the exterior wall of the steel melting shop. HOTLINK system is used when the distance between the direct reduction shaft furnace and the EAF is less than 40 metres.
Hot-melt adhesive – It is an adhesive which is applied in a molten state and forms a bond after cooling to a solid state. It is a bonding agent which achieves a solid state and resultant strength by cooling, as contrasted with other adhesives which achieve the solid state through evaporation of solvents or chemical cure. It is a thermoplastic resin which functions as an adhesive when melted between substrates and cooled.
Hot melt glue – It is a 100 % solid, solvent-free thermoplastic adhesive which turns into a low-viscosity liquid when heated (120 deg C to 180 deg C) and solidifies rapidly upon cooling to form a strong bond. Engineered for high-speed manufacturing, it is mainly used for rapid adhesion, filling gaps, and joining diverse substrates through hot glue guns, nozzles, or rollers.
Hot metal – Hot metal is the output of a blast furnace. It is liquid iron which is produced by the reduction of descending ore burden by the ascending reducing gases.
Hot metal detector – It is the sensor which is necessary to determine the head and the tail of the bar for the bar position tracking.
Hot metal ladle – It is a bucket shaped refractory lined vessel in which hot metal is tapped for its transportation. Hot metal ladle can be open top or torpedo shaped known as open top ladle or torpedo ladle respectively.
Hot metal pretreatment – It consists of a group of metallurgical processes performed on liquid iron after tapping from a blast furnace and before decarburization in a basic oxygen furnace (BOF). Its main purpose is to remove impurities, specifically silicon (desiliconization), phosphorus (dephosphorization), and sulphur (desulphurization), to improve efficiency and improve steel quality.
Hot metal quality – It refers to the chemical composition and physical properties of liquid iron produced in a blast furnace. It is defined by strict constraints on impurities (sulphur, phosphorus, and silicon), temperature, and consistency to ensure high downstream productivity and low refining costs. There are two main qualities of hot metal namely basic grade hot metal and the foundry grade hot metal. Basic grade of hot metal has less than 1 % of silicon, and lower than 1 % of manganese. This type of hot metal is mainly used for steelmaking. There are several grades specified in different standards based on silicon and manganese content of the hot metal. Foundry grade of hot metal is mostly being used in iron foundries as pig iron for remelting and casting into cast iron products. It contains higher amount of silicon. Different standards specify composition limits for silicon and manganese for different grades of this type of hot metal. Silicon content in foundry grade is much higher and normally is in the range of 1.5 % to 3.5 %. It can be as high as 4.25 %. The approximate content of carbon (C) in the hot metal depends on its silicon (Si), manganese (Mn) and phosphorus (P) contents and can be found by using the equation ‘C = 4.6 % – 0.27(% Si) – 0.32(% P) + 0.03(%Mn)’. The temperature of tapped hot metal is to be in the range of 1420 deg C to 1480 deg C.
Hot metal runner – It is a channel or trough which conveys molten iron (hot metal) from the furnace taphole to a receiving vessel, like a torpedo car or open top ladle, for transport to steelmaking facilities.
Hot metal trough – Hot metal trough is a deep trench through which the hot metal and slag flow down once the tap hole is drilled open.
Hot mill – It is a production line or facility for hot rolling of metals.
Hot mix asphalt – It is a combination of around 95 % stone, sand, or gravel bound together by asphalt cement, a product of crude oil. Asphalt cement is heated aggregate, combined, and mixed with the aggregate at a hot mix asphalt facility.
Hot modulus of rupture – It is an important variable in the characterization of refractory materials. Determination of the maximum load at high temperatures is an important parameter for quality control and development of furnace linings. The modulus of rupture is defined as the maximum stress of a rectangular test piece of specific dimensions which can withstand maximum load until it breaks, expressed in mega-pascal. For hot modulus of rupture, load is applied at a high temperature. The international standard test method is described in ISO 5013.
Hot oil quenching – It is a heat-treating process where a heated metal part (typically steel) is submerged into a specialized oil bath kept at a high temperature (frequently 100 deg C to 200 deg C or higher) to achieve high hardness while considerably reducing distortion, cracking, and residual stresses. It is a specialized, slower form of quenching compared to ‘cold’ oil quenching, utilized mainly for complex geometries, high-hardenability alloy steels, and tools that are prone to warping.
Hot pack rolling – It is a specialized metalworking process where two or more layers of metal are stacked, frequently enclosed in a protective metal ‘can’ or canister, and rolled together while heated above their recrystallization temperature. This technique is mainly used to produce thin sheets of materials that are difficult to roll, brittle, or highly reactive at high temperatures, such as titanium alloys, e.g., titanium aluminide (TiAl), magnesium, and superalloys.
Hot piercing – It is also known as roll piercing, rotary piercing, or the Mannesmann process. It is a hot-working deformation process used to create a central cavity in a solid, heated metal billet to produce seamless tubes. It is typically carried out above the metal’s recrystallization temperature, frequently around 1,100 deg C to 1,250 deg C for steel, making the material highly plastic.
Hot plane-strain compression test – It is a metallurgical characterization method which simulates industrial hot-rolling by compressing a thin, wide metal sample between two constrained dies at high temperatures. It creates a 2D strain state (no deformation in the sample width) to measure high-temperature flow stress and study micro-structure evolution.
Hot potassium carbonate process – It is frequently termed the Benfield process. it is a chemical absorption method used to remove high concentrations of high carbon di-oxide (CO2) and hydrogen sulphide (H2S) from gas streams (natural gas, syngas) using hot (100 deg C to 120 deg C) aqueous potassium carbonate (K2CO3) solutions. It is highly energy-efficient for high-pressure, high-partial-pressure applications.
Hot pressed carbon – It is a product containing carbon particles with a carbon binder but with a different manufacturing process. Unlike conventionally baked carbons which can take weeks to bake to volatilize the binders, this process of manufacturing carbonizes the binders in minutes. In this hot-pressing process, a special pressing / carbonizing method is utilized. The carbon particles and binders are mixed and are introduced into a special mould in which a hydraulic ram pressurizes the mixture while, simultaneously, an electric current is passed through the mould, carbonizing the binders. More importantly, as the binders volatilize, the hydraulic ram compresses the mixture which closes off the pores formed by the volatilizing gases as they escape. The resultant product is a very impermeable carbon which can be around 100 times less permeable than conventionally baked carbon. This impermeability is an important property which hat prevents furnace contaminants such as alkali and zinc vapour from penetrating into the hot-pressed brick structure. Additions such as silica and quartz are used to make this hot-pressed carbon more alkali resistant. Normally, alkali materials such as sodium and potassium react with normal carbon to form damaging lamellar compounds that swell, causing volume expansion and spalling of the carbon. However, these alkali materials react preferentially with the silica addition in hot-pressed carbon and form compounds that do not swell, avoiding damaging volume expansion or spalling.
Hot-pressed semi-graphite bricks – These are a type of refractory brick which withstands high temperatures. They are made by combining graphite particles and a carbonaceous binder with silica and quartz materials, and then subjecting the mixture to hot pressing. This process differs from traditional methods by using a combination of pressure and heat to achieve a dense, strong brick with improved thermal conductivity and lower permeability.
Hot-pressed silicon nitride (HPSN) ceramic – It a type of ceramic material made from silicon nitride (Si3N4) powder. It is the fully dense version manufactured in graphite dies typically at temperatures in excess of 1,650 deg C. A small quantity of a hot-pressing aid is typically added, such as 0.5 % to 2 % MgO (magnesium oxide) or 3 % to 8 % Y2O3 (yttrium oxide).
Hot press forging – It consists of plastically deforming metals between dies in presses at temperatures high enough to avoid strain hardening.
Hot pressing – It consists of simultaneous heating and forming of a powder compact. It is a high-pressure, low-strain-rate powder metallurgy process for forming of a powder or powder compact at a temperature high enough to induce sintering and creep processes. This is achieved by the simultaneous application of heat and pressure. Hot pressing is mainly used to fabricate hard and brittle materials. One large use is in the consolidation of diamond-metal composite cutting tools and technical ceramics. The densification works through particle rearrangement and plastic flow at the particle contacts. The loose powder or the pre-compacted part is in most of the cases filled to a graphite mould which allows induction or resistance heating up to temperatures of typically 2,400 deg C. Pressures of up to 50 megapascals (MPa) can be applied. Other major use is in the pressing of different types of polymers, but this is done with lower temperatures and pressures such as those found in the open-source hot press. Within hot pressing technology, three distinctly different types of heating can be found in use: induction heating, indirect resistance heating and field assisted sintering technique (FAST) / direct hot pressing.
Hot pressure-less sintering – It is conventional sintering. It is a powder metallurgy process where a compacted material (green body) is heated in a furnace to high temperatures, below its melting point, to achieve densification solely through atomic diffusion, without applying external pressure. This method enables complex, near-net-shape production but can result in higher porosity compared to pressure-assisted methods.
Hot pressure welding – It is a solid-state welding process which produces coalescence of materials with heat and application of pressure sufficient to produce macro-deformation of the base material. Vacuum or other shielding media can be used.
Hot quenching – It is an imprecise term for different quenching procedures in which a quenching medium is maintained at a prescribed temperature above 70 deg C.
Hot rate – It is the temperature rise of the holding electromagnet over the determined ambient temperature due to the power absorption under voltage. The temperature for reference is normally 35 deg C, if nothing against is indicated.
Hot roll – It is a product which is sold in its ‘as produced state’ off the hot mill with no further reduction or processing steps aside from being pickled and oiled (if specified).
Hot rolled coil – It is a type of flat steel product which is wound into a coil immediately after the final rolling pass. It is produced through a high-temperature rolling process by which a steel slab is rolled in multiple passes at temperature frequently exceeding 1,000 deg C.
Hot rolled heavy sectional products – These products are in the form of beams are either steel joists or parallel flange beams. These products have the characteristics namely (i) the web height is equal to or higher than 80 millimeters (ii) the surfaces of the webs are continued by fillets to the inside faces of the flange, (iii) the flanges are normally symmetrical and of equal widths, and (iv) the outside faces of the flanges are parallel. In case of steel joists, the flanges are of decreasing thickness from the web to the edge. Steel joists are also called sloping flanged beams or tapered flanged beams. In case of parallel flange beams the inner surface of the beams are also parallel and the flanges are of uniform thickness. These beams are also known as universal beams. Beam sections are sometimes slitted in order to obtain two tee sections.
Hot rolled light and medium sectional products – These products consist of several sections namely (i) small channels (‘U’ sections) which are with cross-section resembling the letter ‘U’ and have a height which is less than 80 mm, (ii) angles which are with cross-section resembling the letter ‘L’ with the classification of equal angle and unequal angle depending on the ratio of the flange width and have rounded corner of the flange, (iii) Tee sections which are with equal flanges and the product cross-section resembling the letter ‘T’ and has the rounded corners and equal and slightly tapered flanges and slightly tapered web, and (iv) bulb flats which have a cross-section which is normally rectangular and has a bulge along the full length of a longitudinal edge of one of the wider surface and a width normally less than 430 millimeters.
Hot rolled long sectional products -These are those products which has a cross section resembling a shape such as equal angle, unequal angle, channel, tee, beams (with ‘I’ and ‘H’ sections), and piling section etc. These products are rolled generally in box passes or in universal rolling mills. When the cross-section is rectangular, the dimensional limitations apply to differentiate them from wide flats. These products are mostly delivered in straight lengths, rarely in folded bundles, but never in coils. Depending on the cross-sectional size, the sectional products can be (i) heavy sections, and (ii) light and medium sections.
Hot rolled plate and sheet -These are hot rolled flat products with the edges being allowed to deform freely. These products are supplied flat and normally in a square or rectangular shape, with a width higher than 600 millimeters. The edges may be as-rolled or sheared or flame-cut or chamfered. Hot rolled plate and sheet, according to thickness, can be categorized as (i) sheet when thickness less than 5 millimeters or plate when thickness is 5 millimeters minimum.
Hot rolled steel – it is the steel rolled on a hot rolling mill. Normally, hot rolled steels are further processed into other finished products.
Hot rolled strip – These are flat product which, immediately after the final rolling pass in a hot rolling mill is wound into a coil. Hot rolled strip as rolled has very slightly convex edges, but it can also be supplied with trimmed edges or slit from wider strip. Hot rolled strip, according to its actual width, can be categorized as (i) hot rolled wide strip with a width of 600 millimeters minimum, and (ii) hot rolled narrow strip with a width of less than 600 millimeters. After decoiling and cutting to length, hot rolled narrow strip can be produced as cut lengths.
Hot rolling – It is a metalworking process which shapes metal (typically steel) above its recrystallization temperature, normally over 925 deg C or higher. The process involves passing heated, large, semi-finished products, such as billets, slabs, or ingots, through high-speed rollers to reduce thickness and create a uniform, refined grain structure.
Hot rolling mill – It is that mill in which rolling is done above the recrystallization temperature of the metal. During rolling in this mill, the grains, which deform during the process of rolling, recrystallize, maintain an equiaxed micro-structure and prevent the metal from work hardening. In this type of rolling, hot rolled metal has very little directionality in the mechanical properties and deformation induced residual stresses.
Hot-setting adhesive – It is an adhesive which needs a temperature at or above 100 deg C to set.
Hot shear – It refers to the process of cutting or shearing a material while it is heated, typically to a high temperature. This is normally done to metals, where the heated material becomes more malleable and easier to cut, reducing the force needed for the shearing process and potentially improving the quality of the cut. Hot shears are used in the rolling mills for cropping of front and tail end.
Hot shearing – It is a metalworking process used to cut, separate, or trim metal stock (such as billets, bars, or plates) while the material is at a high temperature (above its recrystallization temperature). By utilizing high-pressure hydraulic or mechanical shears to cut hot metal, the technique considerably reduces the needed cutting force compared to cold shearing, while minimizing material waste and eliminating the need for subsequent energy-intensive cutting processes.
Hot shortness – It is a tendency for some alloys to separate along grain boundaries when stressed or deformed at temperatures near the melting point. Hot shortness is caused by a low-melting constituent, which is frequently present only in minute quantities, that is segregated at grain boundaries.
Hot spot – It is dark gray or black surface patches appearing after anodizing. These areas are normally associated with lower hardness and coarse magnesium silicide precipitate caused by non-uniform cooling after extrusion.
Hotspot area – It is a localized, specific region within a system, component, or geographic space which shows considerably higher values (e.g., temperature, stress, data density, or risk) compared to the surrounding area, frequently leading to performance degradation, failure, or needing intensive, targeted intervention.
Hot spraying – It is also called thermal spraying. It is a surface engineering process which sprays molten or semi-molten materials (metals, ceramics, or polymers) onto a substrate to form a protective or functional coating. Feedstock materials are heated through combustion, electric arc, or plasma, then propelled onto the surface, creating high-density coatings with strong adhesion for improved wear and corrosion resistance.
Hot springs – These are geothermal points on the earth’s surface where water is heated by underlying magma and discharged through rock and soil crevices, frequently leading to the dissolution of minerals which form deposits around the spring. They are typically found in regions with volcanic activity and support diverse microbial life.
Hot stamping – It is also known as press hardening or die quenching. It is a thermo-mechanical manufacturing process which combines forming and heat treatment in one step to create ultra-high-strength steel (UHSS) parts. Steel is heated to austenitic temperatures (around 900 deg C to 950 deg C), formed in a water-cooled die, and rapidly quenched to produce a hardened martensitic structure.
Hot stamping process – It is a hybrid forming technique which involves heating a hardenable steel sheet, forming it in a die, and rapidly cooling it to achieve a hardened martensitic micro-structure, improving its tensile strength. This process is also referred to as press hardening, die quenching, or hot pressing.
Hot steel forging – It is a metallurgical manufacturing process where steel is heated above its recrystallization temperature (typically 1,000 deg C to 1,250 deg C or roughly 75 % of its melting point) and shaped using compressive forces. This high-temperature, malleable state eliminates internal stresses, refines grain structure, and improves ductility.
Hot stove – It is also called hot blast stove. It is a refractory-lined regenerative heat exchanger which preheats blast air to 1,100 deg C to 1,350 deg C for use in a blast furnace. These large, cylindrical towers operate in alternating cycles (on-gas for heating, on-blast for delivering hot air), utilizing waste gases to maximize energy efficiency and enable high-temperature iron smelting.
Hot straightening – It is frequently called heat straightening or flame straightening. It is a repair or rectification process used to correct distortions in metal components, particularly steel, by applying localized, controlled heat. It relies on the principles of thermal expansion and contraction to induce permanent, plastic deformation, allowing a bent or warped member to return to its original shape.
Hot strength – It is also called high-temperature strength. It is the ability of a material to resist deformation, softening, and mechanical failure while operating under high temperatures. It is a critical design factor for ensuring structural integrity, creep resistance, and durability in thermally stressed environments. In foundry, hot strength is the ability of a moulding sand mixture to maintain its shape, structural integrity, and strength at high temperatures, resisting deformation, cracks, or erosion after moisture has evaporated upon contact with molten metal. It ensures the mould remains stable during metal pouring and solidification.
Hot strength, sand – It is the tenacity (compressive, shear or transverse) of a sand mixture determined at any temperature above room temperature.
Hot strip mill – It is a flat rolling mill which rolls hot steel strips from slabs. Hot strips are produced in the form of coils. Hot strip mills in these days are either conventional hot strip mills or strip mills for rolling thin slabs. The primary function of the conventional hot strip mill is to reheat the semi-finished steel slabs (rolled or continuously cast) to the rolling temperatures and then to roll them thinner and longer through a series of rolling mill stands driven by large motors and finally coiling up the lengthened steel sheet for its easy handling and transport. Coils are produced with an inside diameter of 750 millimeters on the coilers, with an outside diameter of up to 2,400 millimeters and with the limitations of coil weight up to 220 kilograms per centimeter of width. The hot strip mill supplies coils for cold rolling mill, strip shearing and slitting units as well as a finished product for shipment directly to the customers. Most material is transported out of the mill area by an automated coil handling system to the storage aisle.
Hot surface – It is a component, equipment, or machinery surface which can heat a combustible mixture to temperatures exceeding its autoignition temperature, enabling localized ignition and sustained flame propagation. The ignition characteristics can be influenced by the surface’s shape, material, and the gas flow parameters. Hot surface represents a substantial thermal hazard for potential fire and explosion in industrial settings.
Hot swaging – It is a hot working, chipless metal forging process used to reduce the diameter, create tapers, or shape the ends of metal work-pieces, specifically tubes, rods, or wires, by heating the material above its recrystallization temperature and applying rapid, radial hammer-like blows using specialized dies. It is distinguished from cold swaging by the application of heat, which makes the metal more ductile and reduces the force needed for deformation.
Hot tack – It is the immediate strength of a heat-sealed plastic film or packaging material, measured while the seal is still hot and molten, before complete cooling or crystallization. Important for high-speed ‘vertical form-fill-seal’ (VFFS) machinery, it ensures the seal holds under the weight of contents before fully solidifying.
Hot tapping – It is the process by which a pipeline under pressure is cut into to provide a side outlet. A flanged fitting is saddle welded to the pipeline and a full port valve bolted to the flange. The hot tapping machine bolted to the outboard valve flange operates through the open valve. After cutting out a circular piece coupon from the pipe wall, the coupon is removed from the pipe by retracting it through the valve and into the chamber of the tapping machine. The valve is then closed and the tapping machine and coupon are then removed from the valve.
Hot tear – It is a fracture formed in a metal during solidification because of hindered contraction. It occurs when low melting point materials segregate during the solidification and hence when they try to shrink during solidification cracks then tears develop since the surrounding material has already solidified. Also, hot tears occur at the joining of thin sections with larger sections because of the difference of the cooling rate and thus solidification. In foundry, hot tear is the irregularly shaped fracture in a casting formed prior to completion of metal solidification resulting from stresses set up by steep thermal gradients within the casting during solidification and too much rigidity of the core or mould material.
Hot tearing – It is a casting defect which occurs during the solidification of a metal when it is still in a semi-solid state. It manifests as cracks or tears in the metal because of the tensile stresses arising from uneven cooling and contraction, particularly when the solid fraction is between 85 % to 95 %. These tears are irreversible and can considerably weaken the final cast product.
Hot tears – Thes are cracks in metal castings formed at high temperatures by contraction stresses.
Hot tensile tests – These are destructive mechanical tests performed at high temperatures to determine a metal’s strength, ductility, and deformation behaviour, such as tensile strength, yield point, and reduction of area, under service-like heat conditions. These tests, frequently guided by ISO (International Organization for Standardization) standard ISO 6892-2, and are important for designing components for high-temperature environments.
Hot tension and compression testing – The testing consists of short-term tests at high temperatures for the determination of high temperature mechanical properties of the metals. The basic methods and Samples are similar to room-temperature testing, although the sample heating, test set-up, and material behaviour at higher temperatures do introduce some additional complexities and special issues for the high temperature testing.
Hot tension behaviour – It refers to the plastic deformation characteristics and mechanical response of a metal or alloy when subjected to tensile stress at temperatures above its recrystallization temperature. It is an important aspect of high-temperature processing (e.g., hot rolling, forging) where materials are to show high ductility and low flow stress to be formed without cracking.
Hot top – It is a reservoir, thermally insulated or heated, which holds molten metal on top of a mould for feeding of the ingot or casting as it contracts on solidifying, hence preventing formation of pipe or voids. It is also a refractory-lined steel or iron casting which is inserted into the tip of the mould and is supported at different heights to feed the ingot as it solidifies.
Hot torsion tests – These involve twisting a heated, cylindrical metal samples at high temperatures (typically higher than 0.6 x melting temperature) to simulate industrial deformation processes like hot rolling, forging, or extrusion. This test measures the material’s flow stress, ductility, and microstructural changes under high-strain, pure shear conditions.
Hot trepanning – it is done to produce a hole through the centre of a large cross section, large mass work-piece. A circular cutter having an outside diameter of the same size as the desired hole and measuring around 25 millimeters in wall thickness and around 203 millimeters in height is initially positioned and pushed into the hot work-piece by the top die while the work-piece is sitting on a lower die with a hole in it. The hot trepanning operation is continued by pushing the followers through the work-piece. These followers have the same inside diameter as the cutter, but a slightly smaller outside diameter (around 13 millimeters, smaller). The followers are locked into position prior to being pushed into the hot work-piece. The length of the followers varies and is based on the length of hot trepanning desired. This hot-trepanning length can be made up by using one or more multiple followers.
Hot trimming –It is a process used to remove excess material, known as flash, from a metal part while the material is still at a high temperature (above its recrystallization temperature) immediately after a forming operation, such as hot forging or hot stamping. It is carried out in a trimming press.
Hot-twist test – It is a method used to assess the forgeability and deformation behavior of metals at high temperatures. It involves twisting a metal specimen at elevated temperatures, simulating conditions encountered during hot working processes like forging. This test helps determine how well a material can be shaped under these conditions and provides valuable data for optimizing manufacturing processes.
Hot upset forging – It is a bulk forming process for enlarging and reshaping some of the cross-sectional area of a bar, tube, or other product form of uniform (normally round) section. It is accomplished holding the heated forging stock between grooved dies and applying pressure to the end of the stock, in the direction of its axis, by the use of a heading tool, which spreads (upsets) the end by metal displacement. It is also called hot heading or hot upsetting.
Hot upsetting – It is a metal forming process which uses high heat and axial pressure to increase the cross-sectional area of a bar or tube end while reducing its length. It is used to produce high-strength, durable components like fasteners, rivets, bolts, and valves by shaping heated metal, frequently in specialized machinery.
Hot utility – It consists of a utility system, such as steam, hot oil, or flue gas, used to supply heat to a process stream, raising its temperature or providing necessary energy for reactions. These systems are necessary for maintaining, operating, and controlling process equipment, frequently selected based on temperature requirements, cost, and efficiency.
Hot vapour – It is a gaseous phase substance, frequently superheated or at high pressure, generated by transferring heat to a liquid (vaporization). It carries substantial latent heat, utilized in systems like steam engines, turbines, and heat exchangers for energy transfer, or produced by reducing pressure.
Hot water – It is the potable or process water heated from ambient temperatures (typically 10 deg C to 25 deg C) to a higher functional temperature, normally ranging between 55 deg C to 60 deg C for domestic use, or up to 200 deg C for industrial heat transfer processes. It is characterized by its high specific heat, stability, and usage in heating, cleaning, and sanitization.
Hot water demand – It refers to the energy requirement for generating sanitary hot water over a specified time period, which is determined by the volumetric consumption of hot water and the temperature difference between the supplied cold water and the desired hot water. It can vary considerably based on user habits, weather conditions, and socio-economic factors.
Hot water distribution systems – These are networks of pipes, valves, and pumps designed to transport heated water efficiently from a source (boiler, heater) to fixtures or HVAC (heating, ventilation, and air conditioning) components. Key factors include selecting circulation methods (one-pipe, two-pipe), ensuring proper insulation to minimize energy losses, and maintaining consistent pressure and temperature throughout the network.
Hot water load – It refers to the calculated energy or volume needed to supply sanitary hot water for domestic or industrial use. It is defined by the required flow rate, temperature rise from cold-water inlet to hot-water outlet, and peak demand duration, typically measured in litres per day or kilo-watts.
Hot water storage tank – It is an insulated pressure vessel used to store heated water (up to 95 deg C) for domestic, commercial, or industrial use. It acts as a thermal buffer, bridging the gap between energy production and consumption to optimize efficiency, manage peak loads, and store heat from solar or boiler systems.
Hot water store – It is an insulated vessel, frequently a tank or cylinder (500 litres to 5,000 plus litres), designed to store heated water (up to 95 deg C) for domestic use, space heating, or industrial processes. It acts as a thermal energy storage (TES) system, managing peak demand, improving efficiency in solar / cogeneration, and bridging supply-demand time gaps.
Hot water system – It is a, centralized or decentralized, infrastructure designed to heat water using a source (gas, electric, solar, heat pump) and distribute it through piping for domestic, commercial, or industrial use. It comprises heat generators, storage tanks, control systems, and frequently recirculation pumps to ensure immediate availability at fixtures.
Hot water tank – It is an insulated vessel designed to store, heat, and supply potable or process water for domestic, industrial, or thermal energy storage applications. Operating on principles of stratification (hot water at top, cold at bottom), these tanks use internal electric elements or external heat exchangers to provide reliable hot water. Hot water tank is a thermal energy storage technology which stores hot water to bridge sunless periods in solar heating systems, improve efficiency in cogeneration systems, and manage peak electricity demand. It is characterized by its reliability, simplicity, and cost-effectiveness in storing sensible heat.
Hot-wire analyzer – It is an electrical atmosphere analysis device which is based on the fact that the electrical resistivity of steel is a linear function of carbon content over a range from 0.05 % carbon to saturation. The device measures the carbon potential of furnace atmospheres (typically). This term is not to be confused with the hot-wire test which measures heat extraction rates.
Hot-wire anemometer – It is an electro-thermal instrument used to measure instantaneous fluid velocity and direction, particularly in gases. It works by measuring the convective heat loss from a fine, electrically heated wire (typically platinum or tungsten) to the surrounding flow, as the cooling effect is proportional to velocity.
Hot wire anemometry – It is a high-resolution, fast-response technique used to measure instantaneous fluid velocity, turbulence, and flow rates. It utilizes a thin electrically heated wire (normally tungsten or platinum) which loses heat through convection to the fluid, with cooling proportional to velocity.
Hot wire barretter – It is a current dependent resistor formed of a fine wire in an envelope. It is useful for regulating current.
Hot-wire probe – It is a precision sensor, typically a micrometer-scale platinum or tungsten wire heated electrically, used to measure instantaneous fluid velocity (gas or liquid) and turbulence by sensing changes in convective heat transfer. As fluid flows past, the wire cools, and its electrical resistance changes. This correlation is used in ‘hot-wire anemometry’ to measure flow rate.
Hot-wire test – It is the method used to test heat extraction rates of various quenchants. Faster heat-extracting quenchants permit more electric current to pass through a standard wire because it is cooled more quickly.
Hot workability – It is the ability of a metal or alloy to undergo substantial shape changes (deformation) at high temperatures, typically higher than 0.6 Tm (melting temperature), without developing cracks, fractures, or structural defects. It is mainly governed by low flow stress, high ductility, and the balance between strain hardening and restoration mechanisms (dynamic recrystallization / recovery).
Hot work die-steels – These steels are high quality steels made to close compositional and physical tolerances. These steels are alloyed tool steels for use in applications in which surface temperature is normally above 200 deg C. During the application the die comes into contact with hot material, the temperatures of which are well above 200 deg C. Besides long -erm thermal load, there is the additional stress due to the periodic change of temperature. Hot work die-steels for such applications have to be able to withstand not only up to the universal mechanical and abrasive stresses normally occurring in die steels, but also, these steels have to withstand thermal load as well. These steels are used to make dies for forming or shaping a material into a part or component adapted for a definite use.
Hot-worked structure – It is the structure of a material which has been worked at a temperature higher than the recrystallization temperature.
Hot working – It is the plastic deformation of metal at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, hence avoiding any strain hardening. It is also referred to as hot forging and hot forming. Hot working is also controlled mechanical operations for shaping a product at temperatures above the recrystallization temperature.
Hot working conditions – These refer to the specific temperature range and strain rate at which deformation occurs while simultaneously allowing recrystallization, thus avoiding strain hardening in materials during processes such as rolling, forging, and extrusion.
Hot working range – It is the temperature interval, typically above a metal’s recrystallization temperature (roughly 0.5 to 0.75 of its melting point, Tm), where material can be plastically deformed without cracking or strain hardening. It allows for extensive, low-force shaping by promoting constant recrystallization to maintain ductility.
Hot-working steels – These steels consist of a specialized type of tool steel designed for applications where they are exposed to high temperatures during use. These steels are characterized by their ability to maintain strength, hardness, and wear resistance at elevated temperatures, making them suitable for hot forming processes like forging, extrusion, and die casting.
Hot working temperature – It is the temperatures above its recrystallization temperature, typically 0.5 to 0.75 times the melting point (Tm in Kelvin). It is the temperature when simultaneous recrystallization takes place, hence preventing strain hardening, reducing yield strength, increasing ductility, and allowing for large deformations.
Hot-work temperature – It is the temperature of the metal at which the plastic deformation of metal conducted. It is above the recrystallization temperature of the metal, typically between 0.5 to 0.7 times the melting point (in Kelvin). This process keeps the metal soft, preventing strain hardening and reducing the required deformation pressure while improving ductility and refining grain structure.
Hot work tool steels – These are specialized, high-alloyed steels designed to withstand extreme temperatures (higher than 200 deg C to 700 deg C), high thermal fatigue, and mechanical wear during hot forming processes. They are classified as Group H steels (H11-H19, H21-H26, H42) and are important for applications involving heat-affected manufacturing, such as die casting, forging, and extrusion.
Hourglass control – It is a numerical technique used in ‘finite element analysis’ (FEA) to stabilize ‘hourglassing’, a non-physical, zero-energy deformation mode that occurs in under-integrated (single-point) elements. It prevents distorted mesh shapes, like ‘hourglassing’, which generate no stress or strain, by introducing artificial stiffness or viscous damping to resist these modes. Hourglass control also refers to techniques used to stabilize spurious modes of deformation associated with zero-energy modes in computational models, ensuring that the nonphysical hourglass energy remains relatively small compared to the peak internal energy.
Hourly basis control – It refers to a, methodology where systems are monitored, modeled, or controlled based on average data values calculated over one-hour intervals. This approach is typically used for long-term planning, load forecasting, and optimizing energy consumption rather than instantaneous (real-time) feedback control.
Hourly energy prices – These refer to the fluctuating costs of electricity which vary throughout the day based on supply and demand dynamics in the market. These prices are categorized into peak prices, which occur during high demand periods, and off-peak prices, which occur during lower demand periods.
Hour-rating – It normally defines the capacity or performance of a system or component over a specific, standardized period, very frequently used to measure energy storage in batteries (Ampere-hours, Ah) or, less frequently, output per hour in thermal systems. It indicates how much load, charge, or service can be sustained for a set duration, often under specific temperature and voltage constraints.
Housekeeping – It is a way of controlling hazards along the path between the source and the worker. Good housekeeping means having no unnecessary items in the work-place and keeping all necessary items in their proper places. Housekeeping at the work-place is closely linked to the industrial safety. The degree, to which this activity is effectively managed, is an indicator of the safety culture of the organization.
House test – It is also called in-house testing. It refers to evaluating products, components, or materials within a manufacturer’s own facilities rather than using external laboratories. This process ensures, through internal expertise and proprietary tools, which products meet specific performance, quality, or compliance standards (e.g., ISO) before market release.
Housing cylinder – It is also called cylinder barrel. It is the pressure-resistant, outer cylindrical shell of a hydraulic or pneumatic actuator. It encloses the piston and piston rod, providing the structural stability, guidance for linear motion, and sealing surface necessary to convert hydraulic or pneumatic energy into force.
Housing-less mill stand – It is also known as an open-type mill stand. It is a type of rolling mill stand which is used in the production of long steel products. It is distinguished by the absence of a housing or frame surrounding the roll stands. It offers higher flexibility and precision.
Housing, rolling mill – Housing creates a framework of the rolling mill stand and for absorbing the total metal pressure on rolls during the process of rolling. Hence, the housing is to be solid and its structure is to enable easy and fast roll changing. Also, there need to be easy access to all parts of the housing and other details of the roll stand. Each of the roll stands has two housings, in which rolls are placed with chocks (bearings). In the upper part of the housing, there are adjusting screws and the roll counter-balancing device along with their drives. From the structural viewpoint, the housings can be classified into three types. These are (i) enclosed housing where the whole housing is made of one piece and which is more beneficial from the strength point of view, (ii) open housing which has the separated cap, connected to the housing by screws for easier rolls changing, and (iii) housing-less roll stand which has rigid chocks connected by solid and pre-stressed joints. The housing-less roll stand has limited stress relaxation (spring-back) of rolls and has smaller and lighter structure.
House of quality – It is the quality function deployment (QFD) which is frequently called the house of quality because of the house shaped quality function deployment matrices. It is a product planning tool which uses a matrix to map the customer wants to the quantified specifications of the design (product). The house of quality approach is used at the first stage of product planning and can be deployed all the way down the stage of production planning on the shop floor.
Howmet process – It refers to advanced, proprietary techniques developed and utilized by Howmet Aerospace, specializing in the investment casting of complex nickel-based and titanium superalloys for high-temperature, aerospace-grade applications (such as jet engine airfoils). The process is renowned for its ability to produce intricate, high-density parts through techniques like ‘single crystal’ (SX), ‘directionally solidified’ (DS), and equiaxed investment casting, combined with hot isostatic pressing (HIP).
H-section – It is also known as H-beam. It is a structural steel profile characterized by its cross-section resembling the letter ‘H’.
H-sections with broad or very broad flanges – These are sections in which the flange width is higher than 0.66 × the nominal height, or 300 mm or over. Sections with flanges wider than 0.8 × the nominal height are sometimes called columns.
HSLA steel – HSLA is the abbreviation for high strength low alloy steel. It is the steel with relatively high strength and impact properties. The carbon level is low and the alloying additions are considerably less than 5 percent.
HTML – It is the abbreviation for HyperText Markup Language. It is the standard foundational markup language used in software engineering and web development to define the structure and content of web pages. It utilizes a system of tags and elements to annotate text, images, and other media for browser rendering.
HTTP – It is the abbreviation for Hypertext Transfer Protocol. It is a foundational, stateless, application-layer protocol, layer 7 of the OSI (open systems interconnection) model designed for distributed, collaborative, and hypermedia information systems. It is the standard language for transmitting data—such as HTML (HyperText Markup Language) documents, images, and videos—between a client (e.g., a web browser) and a web server.
HTTPS – It is the abbreviation for Hypertext Transfer Protocol Secure. It is the secure, encrypted version of HTTP (Hypertext Transfer Protocol), utilizing SSL (Secure Socket Layer) /TLS (Transport Layer Security) protocols to protect data integrity and confidentiality between a client (browser) and server. Operating over port 443, it prevents eavesdropping and tampering by encrypting transmitted data, ensuring authentication of the website through digital certificates.
Hub – It is a boss which is in the centre of a forging and forms a part of the body of the forging. It is also a protruding rim with an external angled shoulder and a sealing mechanism used to join pressure containing equipment.
Hubbing – It is the production of forging die cavities by pressing a male master plug, known as a hub, into a block of metal.
Huber loss – In statistics, it is a loss function used in robust regression, which is less sensitive to outliers in data than the squared error loss. A variant for classification is also sometimes used.
Hub load – It refers to the total force (radial, axial, or bending) acting upon the central hub, bearing, or pulley assembly of a rotating component, such as in belt-driven systems, couplings, or rotor heads. It is categorized into static loads (constant tension / weight) and dynamic loads (variable forces from torque / vibration).
Hubnerite – It is a manganese tungsten oxide mineral with the formula MnWO4.It is classified as the manganese-rich endmember of the wolframite solid solution series (bridging between iron-rich ferberite and manganese-rich hubnerite). It is a vital ore mineral for the extraction of tungsten.
Hue – In colour theory, hue is one of the main properties of a colour, defined technically as ‘the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, orange, yellow, green, blue, violet’, within certain theories of colour vision.
Hue circle – It is a technical, two-dimensional, or 3D colour-space (e.g., ‘hue, saturation, and brightness’, HSB / ‘hue, saturation, and lightness’, HSL) representation arranging spectral hues in a continuous, closed loop. It maps dominant light wavelengths (0-degree to 360-degree) to show colour relationships, complementary pairings, and perceptual transitions. It organizes colours like red, yellow, and green based on human visual perception (opponent signals) rather than linear spectra.
Huet-Sayegh model – It is a linear visco-elastic rheological model used in civil engineering to accurately simulate the complex, temperature-dependent behavior of asphalt materials and mixtures. It combines an elastic spring in parallel with two parabolic creep dashpots (k, h) to model frequency-dependent modulus and relaxation across a wide temperature range.
Huffman coding – It is a lossless data compression algorithm which assigns variable-length binary codes to input characters based on their frequency of occurrence. It is a technique which reduces file sizes by assigning shorter bit sequences to frequently used characters and longer codes to less frequent ones, effectively minimizing the average number of bits per symbol.
Huffman table – It is a data structure, typically a lookup table, which maps symbols (like characters or pixels) to variable-length binary codes based on their frequency of occurrence. It represents an optimal, prefix-free code where high-frequency symbols get shorter codes and low-frequency symbols get longer codes, minimizing total data size.
Huff-n-puff – It is also called cyclic injection. It is an enhanced oil recovery (EOR) technique where a single well undergoes a three-stage cycle namely (i) injection of a fluid (e.g., carbon-di-oxide, steam, or nitrogen) to reduce viscosity, (ii) a soaking period to allow the fluid to interact with the oil, and (iii) production of the oil.
Huge surface area – It refers to an exceptionally high ratio of exposed solid surface to its volume or mass, typically achieved through porous, powdered, or nano-material structures. This enables intensified interfacial interactions, improving properties like adsorption, catalysis, heat transfer, and chemical reactivity.
Huggins interaction parameter – It is frequently denoted as Chi, or the Flory-Huggins parameter. It is a dimensionless quantity in polymer engineering and thermodynamics used to quantify the interaction energy between two components, typically a polymer and a solvent, or two different polymers. It represents the enthalpy of mixing, specifically measuring the difference in interaction energy between a solvent molecule immersed in a pure polymer compared with one in a pure solvent.
Hugoniot pressure – It is the pressure attained by a material under shock compression, representing the locus of thermodynamic states (pressure P, volume V, energy E) reachable behind a shock wave. It is calculated using the Rankine-Hugoniot relations derived from conservation laws, frequently expressed as ‘E2 – E1 = 1/2(P1 + P2) x (V1 – V2)’, where ‘E’ is internal energy, ‘P’ is pressure, and ‘V’ is specific volume.
Hugoniot relation – It is also called Hugoniot equation. It is a fundamental formula defining the thermodynamic states, pressure, volume, and internal energy, across a shock wave. It represents the locus of possible shocked states based on conservation of mass, momentum, and energy (adiabatic process), normally expressed as ‘E2 – E1 = 1/2(P1 + P2) x (V1 – V2)’, where ‘E’ is internal energy, ‘P’ is pressure, and ‘V’ is specific volume.
Hull cell – It is a special electro-deposition cell which is giving a range of known current densities for test work. Hull cell is a trapezoidal box of non-conducting material with electrodes arranged to permit observation of cathodic or anodic effects over a wide range of current densities.
Hull plate steel – It is a specialized type of structural carbon or alloy steel designed specifically for the construction of ship hulls, offshore platforms, and marine infrastructure. It is characterized by high tensile strength, excellent toughness, and superior weldability to withstand harsh maritime environments, impact, and fatigue. These plates are normally produced through hot rolling and, for higher grades, thermo-mechanical control processing (TMCP).
Hull steel – It is the structural steel used in the construction of a ship’s hull, which includes components such as shell plating, framing, bulkheads, and super-structures. It is characterized by its controlled chemical composition, offering good yield strength, ductility, and impact strength, making it suitable for recycling and steelmaking.
Hull structure – It is the main, watertight, 3D framework of a vessel that provides structural integrity, buoyancy, and protection for internal spaces (cargo, machinery, accommodation) against environmental loads like waves and wind. It comprises the outer shell plating and internal stiffening members (frames, longitudinals) designed to withstand bending stresses and buckling.
Human bias – It refers to the systematic, frequently unconscious, errors in judgment, data selection, or interpretation made by engineers and designers which lead to non-neutral, skewed, or discriminatory technical outcomes. These cognitive biases, such as confirmation bias or anchoring, influence design choices, data labeling, and algorithm training, resulting in unfair, unsafe, or inaccurate technological systems.
Human capital – It is also known as human asset. It is a concept to designate personal attributes considered useful in the production process. It encompasses employee knowledge, skills, know-how, good health, and education. Human capital has a substantial impact on individual earnings. Studies have indicated that human capital investments have high economic returns. Organizations invest in human capital, e.g., through education and training, for improving levels of quality and production.
Human-computer interaction – It refers to the design, evaluation, and implementation of computer systems and interfaces which enable researchers, engineers, and technicians to interact with complex computational tools and data-driven systems. It focuses on creating intuitive interfaces which make digital, computational, or robotic technologies in metallurgy more usable, efficient, and safe for analyzing material properties, simulating structures, and automating manufacturing processes.
Human error – It is the term used today to include not just worker’s error, but also engineering deficiency and lack of adequate organizational control which together account for an accident.
Human error probability – It is the term which is used in safety engineering. It is the probability which is assigned to represent the likelihood that a human, normally the operator, fails to complete a particular action correctly.
Human factors – They are those biomedical, psycho-social, work-place environment, and engineering considerations pertaining to people in a human-machine system. Some of these considerations are allocation of functions, task analysis, human reliability, training requirements, job performance aiding, personnel qualification and selection, staffing requirements, procedures, organizational effectiveness, and workplace environmental conditions.
Human interface device (HID) – It is a type of computer device designed for direct interaction between a human and a computer system. It allows users to input data or control functions on a computer. Essentially, it is a device which facilitates communication between humans and computers, typically through input or control mechanisms.
Humanitarian logistics – It is a branch of logistics which addresses the logistical aspects of disaster management, encompassing activities such as procuring, storing, and transporting essential supplies and resources before and after disasters occur.
Human-machine interaction – It refers to the communication and collaboration between humans and machines, encompassing different interfaces and technologies, such as touch interfaces and augmented-reality systems. It is considered a crucial element of Industry, facilitating efficient information management and influencing social dynamics in the work-place.
Human machine interfaces – These are used as an operator control panel to programmable logic controllers (PLCs), remote terminal units (RTUs), and in some cases directly to intelligent electronic devices (IEDs). Human machine interfaces replace manually activated switches, dials, and other controls with graphical representations of the control process and digital controls to influence that process.
Human performance – It is the study of how people interact with systems, combining human capabilities, environmental factors, and tool design to achieve optimal productivity, safety, and accuracy. It models human actions as part of a technical system to predict, prevent, and manage error, balancing speed and accuracy.
Human resources (HR) – It is the set of people who make up the workforce of an organization.
Human resource development (HRD) – it is a process for developing and unleashing human expertise through organization development and personnel training and development for the purpose of improving performance. It is concerned with an organized series of learning activities, within a specified time limit, designed to produce behavioural change in the learner.
Human resource management (HRM) – It is defined as composed of policies, practices and systems which influence employees’ behaviour, attitude and performance. Human resource management practices can play three major roles, namely (i) building of critical organizational capabilities, (ii) enhancing employees’ satisfaction, and (iii) improving customer and stakeholder satisfaction. Proper human resource management practices do make a difference in the working efficiency of the organization. They improve internal capabilities of the organization to deal with current challenges being faced or future challenges to be faced by the organization.
Human systems integration – It is an inter-disciplinary engineering and management process which embeds human capabilities, limitations, and needs into system design, development, and acquisition to maximize total system performance while reducing lifecycle costs. It ensures human-machine compatibility regarding safety, training, and usability, treating personnel as integral to the system.
Hume-Rothery rules – These are named after William Hume-Rothery. These are a set of basic rules which describe the conditions under which an element can dissolve in a metal, forming a solid solution. There are two sets of rules, one refers to substitutional solid solutions, and the other refers to interstitial solid solutions. For substitutional solid solutions, the Hume-Rothery rules are (i) the atomic radius of the solute and solvent atoms differ by no more than 15 %, (ii) the crystal structures of solute and solvent are to be similar, (iii) the complete solubility occurs when the solvent and solute have the same valency (a metal is more likely to dissolve a metal of higher valency, than vice versa), and (iv) the solute and solvent need to have similar electro-negativity. If the electro-negativity difference is too large, the metals tend to form intermetallic compounds instead of solid solutions.
Humic acids – These are complex, high-molecular-weight organic compounds formed from decaying biomass, acting as potent natural chelators and ion-exchange agents. They bind with heavy metals (e.g., iron, nickel, mercury, copper, and cadmium) to form stable, insoluble metal-organic complexes. They are utilized for heavy metal removal in water, ore processing, and radioactive metal transport remediation.
Humic substances – These are coloured relatively recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The colour of humic substances varies from bright yellow to light or dark brown leading to black. Humic substances represent the major part of organic matter in soil, peat, coal, and sediments, and are important components of dissolved natural organic matter in lakes, rivers, and sea water. Humic substances account for 50 % to 90 % of cation exchange capacity in soils.
Humid air – It is also called moist air. It is a binary mixture of dry air and water vapour. It is treated as a mixture of ideal gases where the total pressure is the sum of the partial pressures of dry air and water vapour (Ptotal = Pdry + Pvapour), necessary for calculating heat and mass transfer.
Humid environment – It is an atmosphere with a high concentration of water vapour relative to its temperature and pressure, typically characterized by high ‘relative humidity’ (RH) or dew points. It indicates a condition where air is near saturation, causing accelerated moisture absorption, material degradation (corrosion, mould), and reduced cooling efficiency.
Humidification – It is the unit operation of increasing the water vapour content in a gas stream, typically air, by bringing it into contact with a liquid (normally water). It involves simultaneous mass and heat transfer, where water evaporates into the gas, raising its specific humidity and reducing the air temperature if adiabatic.
Humidifier – It is a device, frequently part of an HVAC (heating, ventilation, and air conditioning) system, designed to increase the moisture content (absolute humidity) of air by releasing water vapour or steam into an enclosed space. It acts as a mass transfer process which adds water vapour to atmospheric air to control humidity levels, normally regulated by a humidistat.
Humidistat – It is a switch which operates automatically on detecting a change in moisture content of the air.
Humidity – It is the concentration of water vapour present in the air. Water vapour, the gaseous state of water, is normally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depends on the temperature and pressure of the system of interest.
Humidity, absolute – It is expressed as either mass of water vapour per volume of moist air (in grams per cubic meter) or as mass of water vapour per mass of dry air (normally in grams per kilogram).
Humidity change – It refers to variations in the quantity of moisture (water vapour) present in a gas, normally air, typically driven by fluctuations in temperature or pressure. As temperature rises, air’s capacity to hold moisture increases, reducing ‘relative humidity’ (RH), while cooling increases relative humidity, which can lead to condensation.
Humidity control – It is the process of managing, regulating, and maintaining the moisture content (water vapour) in the air within a defined space or system, typically measuring ‘relative humidity’ (RH) or absolute moisture levels. It involves adding (humidification) or removing (dehumidification) moisture to ensure thermal comfort, prevent mould, or maintain specific environmental conditions.
Humidity range – It defines the acceptable limits of water vapour in the air for specific applications, processes, or materials, normally expressed as a percentage of ‘relative humidity’ (RH), which ranges from 0 % (completely dry) to 100 % (saturated). Common standards recommend a 30 % to 60 % relative humidity range for human comfort and a 40 % to 70 % range to avoid condensation.
Humidity ratio – It is also known as specific humidity or moisture content. It is the mass of water vapour per unit mass of dry air in a mixture, typically expressed in kilo-gams of water / kilo-grams of dry air. It is a fundamental psychrometric property used in HVAC (heating, ventilation, and air conditioning) systems to calculate latent heat and analyze moisture content independently of temperature changes.
Humidity, relative – It is frequently expressed as a percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature.
Humidity sensing materials – These materials are specialized hygroscopic substances which alter their physical, electrical, or optical properties in response to changes in ambient water vapour levels. Engineered for high sensitivity and rapid response, these materials (e.g., ceramics, polymers, metal oxides, or graphene) interact with moisture, converting humidity levels into measurable electrical (resistance / capacitance) or optical signals.
Humidity sensing property – It refers to the ability of specialized materials (e.g., ceramics, polymers, metal oxides) to alter their physical or electrical characteristics, mainly electrical resistance or dielectric capacitance, in direct response to variations in ambient water vapour (relative or absolute humidity). Engineered sensors detect these moisture-induced changes through adsorption / desorption processes on the surface, offering properties like sensitivity, rapid response, and high stability.
Humidity sensitivity – It refers to the responsiveness of specialized sensors, specifically resistive or capacitive types, to changes in environmental water vapour. It is characterized by measurable electrical variations, such as resistance or capacitance shifts in hygroscopic materials, when exposed to different ‘relative humidity’ (RH) levels, frequently expressed as dRH.
Humidity sensors – These are also called hygrometers. These are electronic devices which detect and measure the concentration of water vapour (moisture) in the air or gases. They are important components which measure ‘relative humidity’ (RH), absolute humidity, or dew point, utilizing changes in electrical capacitance or resistance within a hygroscopic material to provide data for industrial automation, HVAC (heating, ventilation, and air conditioning), and IoT (Internet of Things) applications.
Humidity, specific – It is the ratio of water vapour mass to total moist air parcel mass.
Humidity test – It is an environmental simulation which evaluates a product’s durability, performance, and material stability when exposed to controlled levels of moisture. By placing products in specialized chambers, this testing identifies potential failures like corrosion, delamination, or electrical short circuits, ensuring long-term reliability and adherence to industry standards.
Humidity test and Kesternich-test (sulphur di-oxide) – It is a test for corrosion. In the humidity test, samples are exposed to an atmosphere with 100 % relative humidity. This test can be combined with the addition of a certain amount of sulphur di-oxide gas. This causes a highly corrosive and acidic environment for simulating the effect of heavy pollution normally associated with industry.
Hunter moulding – It is a sand moulding process used to make sand moulds. It refers to the technology developed by Hunter Foundry Machinery Corporation. It also refers to automated, flaskless match-plate moulding machines and related mould handling systems used in the metal casting industry. Hunter moulding machines are horizontally parted match-plate molding machines, as opposed to the Disamatic vertically parted machines. These machines are engineered to rapidly create green sand moulds for high-volume production of castings, such as iron and aluminum.
Hunter process – It is a historic method for producing high-purity titanium metal by reducing titanium tetra-chloride (TiCl4) with sodium (Na) at high temperatures, normally around 1,000 deg C. It has been the first industrial process for titanium, typically yielding fine, high-purity sponge titanium, although it has been was largely superseded by the Kroll process.
Hurst coefficient – It is a measure which relates to the fractal dimension of a surface, where a lower Hurst coefficient indicates a higher fractal dimension and influences the power density spectrum around the specular direction in scattering behaviour.
Hurwitz matrix – It is a structured, real square matrix formed from the coefficients of a characteristic polynomial of a linear time-invariant system. It is used to determine stability, where a system is stable if all eigenvalues of the matrix have strictly negative real parts, meaning all leading principal minors of the matrix are positive.
Hurwitz stability criterion – It refers to a mathematical test used to determine the stability of a linear time-invariant (LTI) control system, stating that a polynomial is Hurwitz if all the principal minors of its associated Hurwitz matrix are strictly positive.
Husk fibre – It is a biodegradable material derived from agricultural waste, such as corn husks, which exhibits significant mechanical, thermal, and chemical properties, making it suitable for applications in composite materials, insulation, and several eco-friendly products.
Huygens’ principle – It is a method for understanding wave propagation, stating that each point on a wave front acts as a source of secondary wavelets, which collectively form the new wave front at a subsequent moment. This principle can be applied to describe how light behaves as it travels through different media, leading to phenomena such as refraction.
HVAC – It is the abbreviation for ‘heating, ventilation, and air conditioning. It refers to the technology and sub-discipline of mechanical engineering focused on environmental comfort and indoor air quality (IAQ). It involves designing systems based on thermodynamics, fluid mechanics, and heat transfer to regulate temperature, humidity, and air purity in residential, commercial, and industrial spaces.
HVAC drawing – HVAC (heating, ventilation, and air conditioning) drawing provides information about the heating and ventilation systems. It also includes the air conditioning patterns and layout which are to be constructed inside the building. The HVAC drawing provides an insight into these complex systems and helps in planning the construction process accordingly. The HVAC plan is a schematic diagram which visually represents the structure and components of mechanical systems installed for thermal comfort, air-conditioning, and better air quality. HVAC symbols are used to depict the layout of devices, ventilation network, and other components of a HVAC system. The purpose of using HVAC symbols is to design an accurate HVAC plan which satisfies the environmental requirements of comfort by adjusting the outdoor air conditions. There are two common types of HVAC plans. The central HVAC plan is used when the need is to locate the system away from the building. It uses delivery ductwork to deliver the conditioned air. The local HVAC systems are normally positioned near or inside the conditioned zone with ductwork requirements.
HVDC power transmission – Full form f HVDC is high voltage direct current. HVDC power transmission is the method of transmitting electricity generated from power plants over high-voltage direct current lines to end users, which allows for efficient long-distance power transfer and the connection of networks operating at different frequencies. It utilizes switching valves, traditionally made from thyristors, and more recently from insulated-gate bipolar transistors (IGBTs), to control the flow of unidirectional direct current.
Hybrid – It is a composite laminate consisting of at least two distinct types of matrices or reinforcement. Each matrix or reinforcement type can be distinct because of its (i) physical and / or mechanical properties, (ii) material form, and (iii) chemical composition.
Hybrid actuator – It is a system combining two or more distinct actuation technologies (e.g., hydraulic, electric, pneumatic, or smart materials) to leverage their respective strengths, such as high force density, energy efficiency, and precise controllability, while overcoming individual limitations. They frequently eliminate external plumbing by integrating motors, pumps, and reservoirs into a single, compact, self-contained unit.
Hybrid amplifier – It is a design combining two distinct amplification technologies, typically vacuum tubes for preamplification (warmth) and solid-state transistors such as metal–oxide–semiconductor field-effect transistors (MOSFETs) for the power output stage. This approach optimizes for both audio fidelity / tone and high efficiency / reliability, utilizing each technology’s strengths.
Hybrid automaton – It is a formal modeling framework combining discrete state-transition systems with continuous, time-dependent, real-valued variables to describe systems containing both digital control and analog physical components. They define behaviours using states, differential equations for continuous flows, and guards for discrete mode transitions.
Hybrid belts – These belts combine merits of the flexibility of nylon belt and low elongation of polyester belt. Satisfactory improvement is confirmed on those lines where belts are lengthened since sufficient take-up stroke is not secured.
Hybrid coder – It is a system which combines two or more distinct, traditional coding or coding-related methods to achieve better performance, such as higher compression ratios, lower computational complexity, or increased robustness, than any single technique could provide on its own. In the context of video, image, or signal compression, these systems frequently integrate predictive coding, transform coding (like discrete cosine transform, DCT), and vector quantization (VQ) to optimize data transmission and storage.
Hybrid coil – It is a kind of transformer which is used for bi-directional transmission of signals over one pair of wires.
Hybrid composite – It is a material consisting of a single matrix combined with two or more different types of reinforcing fibers or particles to achieve superior, tailored, or synergistic properties. By combining materials (e.g., carbon / glass, natural / synthetic), engineers can balance strength, stiffness, toughness, and cost, optimizing performance beyond what a single-reinforcement composite can offer.
Hybrid configuration – It refers to a system, device, or network which integrates two or more distinct, frequently contrasting, technologies or components to improve efficiency, performance, or flexibility. Key examples include power electronics combining alternating current / direct current (AC / DC), vehicles blending internal combustion engines with electric motors, and IT (information technology) systems merging on-premises infrastructure with cloud services.
Hybrid control – It refers to systems which integrate continuous-time (analog) dynamics with discrete-event (digital / logic) controllers to manage complex, multi-modal processes. It combines the smooth operation of physical plants (e.g., motors, chemical reactors) with the decision-making logic of digital computers, e.g., switches, programmable logic controller (PLCs) to optimize performance, safety, and efficiency.
Hybrid control strategy – It integrates multiple, distinct control methods, such as combining model-based algorithms with data-driven techniques, or continuous controllers with discrete logic, to optimize performance, stability, and efficiency. It adapts to changing system behaviours by switching between algorithms or using them simultaneously to mitigate non-linearities and disturbances.
Hybrid cycle – It refers to a system or machine which combines two or more distinct technologies, energy sources, or thermodynamic cycles to improve efficiency, performance, and operational flexibility while minimizing fuel consumption and emissions. It frequently merges continuous and discrete dynamic behaviours or integrates renewable sources.
Hybrid desalination system – It is the combination of two or more, normally distinct, desalination technologies, typically blending thermal distillation (e.g., multi-stage flash / multi-effect distillation, MSF / MED) and membrane processes (e.g., reverse osmosis, RO), into one integrated unit. These systems optimize water recovery, reduce specific energy consumption, and manage brine waste, enhancing overall efficiency and operational flexibility compared to standalone plants.
Hybrid electric vehicle – It is a vehicle combining an internal combustion engine (ICE) with an electric motor and battery, engineered to improve fuel efficiency and reduce emissions. It uses two propulsion sources, fuel and electricity, without needing external charging, relying instead on regenerative braking and the engine to recharge the battery.
Hybrid energy – It the use of multiple energy sources, such as solar, wind, mechanical, thermal, or electromagnetic fields, to generate a more reliable and efficient electrical power supply.
Hybrid energy storage system – It is the combination of two or more, different, complementary energy storage technologies, such as batteries, supercapacitors, or flywheels, within a single operating system to optimize energy and power density. It overcomes limitations of single-source systems (e.g., poor lifespan or slow response) by leveraging the high energy density of one component (e.g., battery) with the high-power density of another (e.g., super-capacitor).
Hybrid energy system – It is the integration of two or more, normally renewable, power sources (e.g., solar photo-voltaic, wind, hydro) combined with storage technologies (batteries) or backup generators to create a more reliable, stable, and efficient power supply. It mitigates the intermittency of single sources by pairing them, such as solar-wind or photo-voltaic-diesel systems, optimizing energy output and reducing fossil fuel reliance.
Hybrid experiment – It is a testing methodology which combines physical, real-world testing of components with numerical computer simulations in real-time. This approach uses sensors, actuators, and controllers to create a closed-loop system, allowing researchers to evaluate complex, large-scale structures (like buildings under seismic loads) accurately while reducing cost and time.
Hybrid fillers – These are combinations of two or more distinct types, sizes, or morphologies of filler materials (e.g., carbon nano-tubes with carbon black, or nano-particles with micro-particles) incorporated into a polymer matrix. They are engineered to produce synergistic effects, improving mechanical (strength, hardness), thermal, or electrical properties beyond what a single filler can achieve.
Hybrid filter – It is a system combining two or more distinct filtration technologies, typically passive (inductors / capacitors) and active (power electronics) in power systems, or electrostatic precipitators (ESP) and fabric filters in emission control, to achieve higher efficiency, better performance, and lower operating costs than either method alone.
Hybrid fossil-energy systems – These are power generation or industrial configurations which combine conventional, non-renewable, hydrocarbon-based fuel sources (such as coal, oil, or natural gas) with renewable energy inputs (such as solar, geothermal, or biomass) within a single, integrated facility. The goal of this approach is to maximize overall thermodynamic efficiency, mitigate the intermittency of renewable sources, and reduce greenhouse gas (GHG) emissions compared to standalone fossil fuel plants.
Hybrid grid – It refers to a system combining multiple, distinct technologies to optimize efficiency, reliability, and power quality. It normally refers to two main concepts, namely (i) electrical power systems integrating alternating current and direct current sources / loads with storage, or (ii) computational fluid dynamics (CFD) using combined tetrahedral / hexahedral grids for complex geometries.
Hybrid image – It is a computer vision technique creating a static image with two interpretations, changing based on viewing distance. It combines high spatial frequencies (fine details) of one image with low spatial frequencies (blurred, coarse shapes) of another, relying on human visual system multi-scale processing. Up-close, the high-frequency image dominates; from afar, the low-frequency image becomes visible.
Hybrid integrated circuits – These are miniaturized electronic circuits fabricated by combining semi-conductor devices (transistors, diodes, or integrated circuit chips) and passive components (resistors, capacitors, inductors) on a single insulating substrate (ceramic or glass). They utilize thick or thin-film technology for interconnections, providing high density, high reliability, and design flexibility, frequently used in several applications.
Hybridization – It refers to the concept of combining different technologies, materials, or processes to create a new, improved system or product. This intermixing can result in enhanced performance, functionality, or efficiency compared to using any of the individual components alone. It is a strategy used to leverage the strengths of multiple elements to overcome limitations or achieve novel solutions.
Hybridized carbon – It refers to the process of mixing atomic ‘s’ and ‘p’ orbitals to form new, equivalent hybrid orbitals (‘sp’, ‘sp2’, ‘sp3’) with distinct energies and shapes. This process, necessary for tailoring molecular geometry and strengthening bonds, enables the creation of diverse carbon allotropes (graphite, diamond, graphene) with unique electronic, mechanical, and structural properties.
Hybridized system – It is an integration of two or more, frequently disparate, technologies, methods, or energy sources designed to work together to improve overall performance, efficiency, and reliability while mitigating the individual drawbacks of each component. This approach is increasingly used to optimize systems, such as combining renewable energy (solar, wind) with conventional power sources (diesel) or incorporating energy storage (batteries, hydrogen) to manage intermittency and reduce operating costs.
Hybrid joining – It is the combination of two or more distinct joining techniques (e.g., adhesive bonding with mechanical fastening or welding) to create superior joints. It merges techniques to improve strength, stiffness, fatigue resistance, and durability, often used to join dissimilar materials in different industries.
Hybrid laminar flow control – It is an aeronautical technique designed to reduce aerodynamic drag and fuel consumption by maintaining smooth (laminar) airflow over surfaces (wings, nacelles) for a longer distance. It combines shaping (natural laminar flow) with active suction through porous skins to suppress boundary layer turbulence.
Hybrid laser-arc welding – It is an advanced joining process which simultaneously combines laser beam welding (LBW) and arc welding (typically metal inert gas, MIG / metal active gas, MAG) within a single weld pool. It merges the deep penetration of lasers with the filler metal capability and gap bridging of arcs, resulting in high-speed, high-quality welds with low heat input.
Hybrid machining processes – These processes combine two or more traditional and / or non-traditional manufacturing methods simultaneously at the same zone of interaction to improve material removal rates, reduce tool wear, and improve surface integrity. These processes, such as laser-assisted turning or electro-chemical grinding, are specifically designed to handle hard-to-cut materials and create complex, high-precision components.
Hybrid market – It is a trading environment which simultaneously accommodates both physical and electronic trading methods for the same products, aiming to combine the advantages of each format.
Hybrid maximum power point tracking – It is a control strategy which combines two or more distinct techniques, typically a fast-tracking algorithm, e.g., ‘perturb and observe’ (P&O), incremental conductance (INC) and an intelligent / heuristic method, e.g., fuzzy logic, ‘particle swarm optimization’ (PSO), artificial neural network (ANN), to maximize power extraction from photo-voltaic. It overcomes limitations of single methods by providing rapid convergence, high accuracy, and minimal oscillations, particularly under partial shading conditions.
Hybrid membrane – It is a material combining organic (polymeric) and inorganic (metal oxides, carbon) components to improve properties like strength, permeability, and antifouling. These materials create a synergistic effect, overcoming limitations of single-material membranes to improve separation efficiency in water treatment, fuel cells, and chemical processes.
Hybrid method – It combines two or more algorithms, techniques, or processes to leverage their respective strengths and mitigate individual limitations. It improves performance, reduces processing time, and increases robustness by merging approaches like simulation, machine learning, or physical processes.
Hybrid modeling – It is the combination of mechanistic (first-principles) modeling and data-driven approaches (machine learning) to simulate complex systems. It uses known physical laws (mass balance / energy balance) for well-understood parts and data-driven methods for unknown kinetics or complex interactions. This approach enables accurate, reliable predictions, especially when data is scarce or systems are complex.
Hybrid model predictive control – It is an advanced control strategy which optimizes system performance over a future horizon by managing processes containing both continuous dynamics (e.g., temperature, velocity) and discrete logic (e.g., valves, switches, gears). It utilizes ‘mixed logical dynamical’ (MLD) frameworks or piecewise affine models to solve ‘mixed-integer quadratic programme’ (MIQP) in real-time.
Hybrid motor – It is an electric machine combining two or more distinct operating principles or technologies, typically permanent magnets and variable reluctance, to improve torque, efficiency, and speed control. These motors, frequently used as stepper motors, utilize an axially magnetized rotor and an electro-magnetically energized stator for high-precision, high-torque, and high-efficiency performance.
Hybrid multi-stage scheme – Within computational fluid dynamics (CFD) and numerical analysis, It is an advanced numerical time-stepping technique within combines two or more different numerical approaches (e.g., central and upwind schemes) across multiple stages. The main purpose of this hybrid approach is to leverage the advantages of individual methods, specifically high-order accuracy in smooth regions and robust stability in the presence of shocks or discontinuities, while optimizing computational efficiency.
Hybrid nano-fluids – These are advanced heat transfer fluids engineered by dispersing two or more distinct types of metallic, non-metallic, or polymeric nano-particles into a base fluid (e.g., water, oil) to create a composite mixture. They improve thermal conductivity, heat transfer rates, and lubrication better than mono-nano-fluids, important for high-heat-flux engineering.
Hybrid observer – It is a state estimation system designed for hybrid plants, systems featuring both continuous-time dynamics and discrete-event jumps (e.g., switches, impacts). It combines a location observer (identifying the discrete state) and a continuous observer (estimating continuous states) to provide accurate, frequently exponentially convergent, state estimation.
Hybrid perovskites – These are organic-inorganic crystalline compounds (ABX3) combining organic cations (e.g., methyl-ammonium) with inorganic metal halides (e.g., Lead-Iodide), engineered for high-performance opto-electronics like solar cells. They offer tunable bandgaps, high absorption, and low-cost solution processing. Engineering focuses on stability through compositional tuning (mixing A/X sites) and dimensional control (3D to 2D).
Hybrid photovoltaic-wind power plant – It is an engineered energy system combining solar photo-voltaic arrays and wind turbines to generate electricity, frequently integrated with battery storage to mitigate intermittency. It increases overall system efficiency and reliability by leveraging complementary generation patterns (e.g., wind at night / winter, sun during day / summer).
Hybrid plant – It is a facility which integrates two or more different energy sources, technologies, or operational methods (such as solar / wind or renewable / fossil fuel) at a single connection point to maximize efficiency, reliability, and sustainability. It combines technologies to optimize performance, manage intermittency, and improve land usage.
Hybrid position-force control – It is a robotics engineering technique which simultaneously manages a robot’s end-effector position (trajectory) and interaction force by splitting control into independent, complementary subspaces based on task geometry. It uses force / torque sensors to regulate contact forces in restricted directions while maintaining precise position control in free directions.
Hybrid powder – It is a composite material created by blending two or more distinct, typically inorganic and organic components (e.g., polymers with metallic / ceramic nano-particles) to achieve synergistic properties, such as improved mechanical strength, improved processing, or functional coatings. It is mainly used in advanced additive manufacturing and coatings.
Hybrid power system – It integrates two or more energy generation methods, typically combining renewables like solar (photo-voltaic) and wind with battery storage or conventional diesel generators. These systems optimize performance through shared infrastructure and smart controls to increase reliability, efficiency, and stability compared to single-source power supplies, especially in off-grid or micro-grid applications.
Hybrid power-train – It is an automotive propulsion system combining an internal combustion engine (ICE) with one or more electric motors and a battery, allowing for separate or combined operation. Engineered to maximize fuel efficiency and reduce emissions, these systems use power electronics to manage energy flow between fuel and electric sources.
Hybrid process – It combines two or more manufacturing or production processes simultaneously or sequentially to achieve superior, synergistic performance (the ‘1+1=3’ effect) which can neither achieve alone. These systems integrate different energy sources, tools, or mechanisms to increase productivity, improve accuracy, and enhance surface quality. It involves the simultaneous and controlled interaction of process mechanisms/tools within the same processing zone (e.g., laser-assisted turning) or a combination of sequential steps on one machine platform.’
Hybrid processing – It refers to the combination of two or more, normally distinct, manufacturing or processing technologies (e.g., thermal, chemical, mechanical) in a single, integrated setup to improve performance, increase material removal rates, improve surface finish, or achieve complex geometries which single processes cannot. It frequently follows a ‘1 + 1 = 3’ principle, where the synergy of techniques yields superior efficiency.
Hybrid pyro-hydrolysis acid regeneration processes – When the main purpose in the operation of a pyro-hydrolysis plant is the production of high-quality iron oxide powder, then a reactor design which combines the energy efficiency of a spray roasting furnace with the homogeneous and stable process conditions of a fluidized bed process is adopted. This needs higher investments in the de-dusting and gas quenching technologies.
Hybrid renewable energy system – It is an approach combining two or more renewable energy sources (e.g., solar photo-voltaic, wind, hydro, biomass) with energy storage or conventional back-ups. Engineered to improve reliability, efficiency, and sustainability, these systems compensate for intermittent, weather-dependent generation, providing a more stable power supply than single-source systems.
Hybrid resin – It is a composite material which combines two or more different resin types (e.g., organic and inorganic, or epoxy and silicone) or mixes distinct filler particles to achieve superior performance properties. They are designed to improve strength, reduce polymerization shrinkage, and improve durability, typically combining the best properties of their components.
Hybrid riser – It is a deep-water production system combining rigid steel vertical pipes (for structural strength) with flexible jumpers (for motion compliance) to connect subsea wells to floating platforms. It reduces top-tension loads and fatigue, designed to withstand harsh environments by decoupling the main riser from surface vessel motion.
Hybrid solar cells – These are next-generation photovoltaic devices which combine organic materials (polymers, dyes) with inorganic semi-conductors, e.g., titanium di-oxide (TiO2), cadmium selenide (CdSe), silicon (Si) in a single active layer. They combine the high absorption / electron mobility of inorganics with the low-cost, flexible processing of organics, aiming to optimize performance while reducing costs.
Hybrid state – It refers to a, often time-varying, combination of continuous dynamic behaviours (described by differential equations) and discrete, event-driven switching (described by automata or state machines) that characterizes a complex system. These systems allow for modeling phenomena that ‘flow’ and ‘jump’, such as a controller activating a pump based on a pressure threshold.
Hybrid strategy – It integrates two or more distinct, frequently opposing, approaches, such as cost leadership and differentiation, or agile and waterfall methodologies, to optimize performance, flexibility, and value. It leverages the strengths of combined methods to overcome limitations of single-approach strategies, frequently aiming to boost efficiency and adaptability in complex systems.
Hybrid structure processing – It involves the simultaneous, controlled application of multiple, distinct manufacturing mechanisms, energy sources, or tools within a single process zone to improve performance, efficiency, and material properties. These techniques (e.g., laser-assisted machining, adhesive-rivet joining) reduce process chains, lower energy consumption (frequently by around 20 %), and improve structural strength.
Hybrid sulphur cycle – It is also called Westinghouse cycle. It is a two-step thermo-chemical water-splitting process for large-scale hydrogen production. It combines high-temperature sulphuric acid decomposition (800 deg C and above) with low-temperature SO2-depolarized electrolysis (below 100 deg C), sulphur compounds to efficiently split water into hydrogen and oxygen. The cycle consists of two main reactions, designed for high-efficiency energy conversion, frequently coupled with nuclear or solar heat sources, namely (i) step 1 – electrochemical cell (anode) ‘SO2 + 2H2O = H2SO4 + H2’, (produces hydrogen and sulphuric acid), (ii) step 2 – thermo-chemical decomposition (reactor) ‘H2SO4 = SO2 + H2O + 1/2 O2’, (high-temperature decomposition to recover and produce oxygen).
Hybrid test – It merges physical, real-time experiments with numerical, computer-based simulations to evaluate complex systems efficiently. It couples physical components (e.g., structural parts) with computer models of the rest of the structure to save costs and enable realistic testing scenarios. This approach ensures comprehensive validation.
Hybrid time – It is a framework which combines continuous physical time (modeled by differential equations) with discrete, instantaneous time (modeled by difference equations or events) to model complex dynamic systems. It allows for the analysis of systems which switch between different modes of operation, such as mechanical components controlled by digital computers, where continuous evolution (flow) is interrupted by instantaneous discrete transitions (jumps).
Hybrid topology – It is a network engineering design which combines two or more different fundamental network topologies (e.g., star, bus, ring, or mesh) into a single, cohesive network structure. It is used to leverage the strengths of each topology, such as high reliability, scalability, and flexibility, while reducing the limitations of individual, simpler structures.
Hybrid traction mode – It refers to an operating state in hybrid electric vehicles (HEVs) where the internal combustion engine (ICE) and electric machine(s) work together simultaneously to deliver torque to the drivetrain. This mode optimizes power output, typically enabling high acceleration or assisting with heavy loads.
Hybrid wind system – It is an integrated power generation setup combining wind turbines with other energy sources, normally solar photo-voltaic (PV), diesel generators, or battery storage, to ensure a reliable, continuous power supply. These systems leverage complementary, energy production patterns (e.g., higher wind in winter / night, higher solar in summer / day) to improve efficiency and stability.
Hybrid yarns – These are multi-component textile strands combining two or more distinct fibre types (e.g., carbon / thermoplastic, aramid / cotton) in a single structure to achieve superior performance properties. Designed for specific engineering needs, these are used in high-performance composites, technical textiles, and protective apparel.
HYBRIT process – It replaces coal with hydrogen for the direct reduction of iron, combined with an electric arc furnace. The process is almost completely fossil-free, and result into substantial reduction in its greenhouse gas emissions. The product from the hydrogen-direct reduction process is direct reduced iron or sponge iron, which is fed into an electrical arc furnace, blended with suitable shares of scrap, and further processed into steel. The main characteristics of the process are (i) non fossil fuels are used in iron ore pellet production, (ii) hydrogen is produced with electrolysis using fossil-free electricity, (iii) storage of hydrogen in a specially designed unit is used as a buffer to the grid, (iv) a shaft furnace is used for iron ore reduction, (v) tailor-made pellets are used as iron ore feed, (vi) the reduction gas / gas mixture is preheated before injection into the shaft, (vii) the product can either be direct reduced iron or hot briquetted iron free of carbon or carburized, and (viii) the direct reduced iron / hot briquetted iron is melted together with recycled scrap in an electric arc furnace.
Hydra-film process – It is also known, also known as the thick-film process. It is a variation of hydro-static extrusion. In this process, the volume of the hydrostatic medium is kept so low that the stem can contact the billet during extrusion. The stem speed is then the same as the billet speed. This occurs, as per the equation ‘Ubillet = Ustem x (Astem/Abillet)’, where the ‘Ubillet’ is the speed the billet, ‘Ustem’ is the speed of the stem, ‘Astem’ is the cross-sectional area of the stem, and ‘Abillet’ is the cross-sectional area the billet, if the billet cross-sectional area is around the same as the container cross-sectional area. Hence, in the hydra-film process, there is merely a thin film of the hydrostatic medium between the billet and the container as well as between the billet and the stem. The stem speed is equal to the billet speed, since the billet cross-sectional area is around the same as the container cross-sectional area. This process offers several advantages over conventional hydrostatic extrusion.
Hydrant valve – It is also called landing valve. It provides the means to draw water for fire-fighting from the fire water piping network.
Hydra-pulper – It is a large mixing vessel equipped with one or more revolving agitators which provides circulation and energy to disperse pulp fibres in water during the papermaking process.
Hydrate – A hydrate is a substance which contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which have been so labeled before their chemical structure has been understood. An example of hydrate is aluminum oxide with three molecules of chemically combined water. Hydrates represent critical blockage risks in pipelines, demanding mitigation.
Hydrate blockage – It refers to the accumulation of crystalline solid compounds, formed by water and natural gas components under low temperature and high pressure, which restricts or completely plugs oil and gas pipelines, production equipment, or subsea flowlines. These, frequently called ‘methane hydrates’, deposit on pipe walls, agglomerate, and create substantial flow assurance risks, needing, for example, depressurization, heating, or chemical inhibitors to remove.
Hydrate control – It involves methods to prevent or manage the formation of solid, ice-like water / hydrocarbon crystals in oil and gas systems (pipelines, subsea) which cause blockages. It utilizes thermodynamic inhibitors, e.g., methanol, mono-ethylene glycol (MEG) to shift equilibrium, or kinetic inhibitors / anti-agglomerants to manage growth.
Hydrated cement – It is the product resulting from the reaction of non-hydrated cement with water, which involves both chemical and physico-mechanical changes, leading to processes such as setting and hardening. Hydrated cement is the solid, binding, and hardened material formed through the exothermic chemical reaction (hydration) between hydraulic cement particles (mainly silicates and aluminates) and water. It transforms paste from a plastic to a solid state, producing calcium silicate hydrate (C-S-H) gel and calcium hydroxide.
Hydrated cement paste – It is the solid, engineered binding matrix formed by the chemical reaction (hydration) between cement powder and water. It consists mainly of calcium silicate hydrate (C-S-H) gel (50 % to 60 %), calcium hydroxide [Ca(OH)2] crystals (20 % to -25 %), unhydrated cement, and pore spaces. This porous material bonds aggregates in concrete, gaining strength through curing.
Hydrated ion – It is an ion surrounded by a shell of water molecules, formed when ionic compounds dissolve in water, with water molecules orienting around ions due to electro-magnetic attraction. This process defines the ‘hydration shell’ or ‘solvation shell, influencing ion mobility, reaction rates, and solution properties.
Hydrate dissociation – It is the endothermic process where solid gas hydrates break down into water and gas because of the pressure reduction or temperature increase. This phase change, frequently in pipelines, absorbs substantial heat, causes high localized pressure, and needs careful monitoring to prevent flow blockage.
Hydrate dissociation temperature – It is the specific temperature, dependent on pressure and composition, at which solid gas hydrates become thermodynamically unstable and decompose into water and gas. It represents the upper thermal boundary of stability (frequently termed the dissociation curve), below which hydrates form and above which they break down.
Hydrated materials – These materials are substances which contain water molecules chemically combined within their crystal structure or physically absorbed, frequently with a definite ratio of water to the host compound (M.nH2O). They are used for structural hardening (concrete), thermal energy storage, and in specialized hydrogels.
Hydrated salt – It is an ionic compound (salt) with water molecules incorporated into its crystal lattice structure, represented as (M.nH2O). These compounds, frequently used as phase change materials (PCMs) for heat storage, contain a fixed quantity of ‘water of crystallization’ which can be removed through heating (dehydration) and reabsorbed.
Hydrated sample – It refers to a material (such as cement, soil, or polymers) containing chemically or physically bound water within its structure, or a substance which has undergone hydration (e.g., curing). These samples need specific handling because of their delicate, ‘wet’ nature, frequently demanding specialized techniques like cryo-SEM (scanning electron microscope) for analysis, as they are prone to structural changes when dried.
Hydrate formation – It is the crystallization process where water molecules form cage-like structures (clathrates) around light hydrocarbon gases (e.g., methane, ethane) or carbon di-oxide (CO2) under high-pressure, low-temperature, and turbulent conditions. These ice-like, non-stoichiometric solids (around 85 % water) plug pipelines and equipment, posing severe flow assurance risks in oil and gas operations.
Hydrate formation curve – It is a thermodynamic boundary on a pressure-temperature (P – T) plot defining the conditions where water and light hydrocarbons (methane, ethane, etc.) coexist as solid, ice-like crystals. It separates a safe operating region (low ‘P’, high ‘T’) from a hydrate formation region (high ‘P’, low ‘T’), identifying when pipelines risk blockage.
Hydrate formation temperature – It is the maximum temperature at which solid gas-water crystals (hydrates) begin to form from a gas mixture at a specific high pressure and in the presence of free water. It represents the phase boundary, typically well above 0 deg C, where gas hydrates, water, and gas coexist in equilibrium.
Hydrate inhibitors – These are chemicals used to prevent the formation of hydrates in hydro-carbon systems, with thermodynamic inhibitors such as alcohol, glycol, and ionic salts being the most common types. They include both traditional inhibitors like methanol and low dosage inhibitors such as kinetic inhibitors and anti-agglomerants.
Hydrates, natural gas – These hydrates are solid, ice-like crystalline compounds (clathrates) formed when water molecules cage gas molecules (mainly methane) under high-pressure and low-temperature conditions. They represent substantial flow assurance risks, creating solid plugs that block pipelines, yet are also considered unconventional energy resources.
Hydration energy – It is also known as hydration enthalpy. It is the energy released when one mole of gaseous ions dissolves in water to form hydrated ions, typically measured in kilo-joules per mol. It is an exothermic process (- delta H) representing the strength of ion-dipole interactions, where smaller ions with higher charge density generate higher heat, influencing solubility and material stability.
Hydration force – It is a strong, short-range (typically below 3 nano-meters) repulsive force acting between polar, hydrophilic surfaces separated by a thin water layer. It arises from the energy needed to dehydrate surfaces, frequently exceeding DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory predictions. These forces are important in colloidal stability, and swelling clays.
Hydrate inhibitors – These are chemicals used in oil and gas engineering to prevent the formation of solid gas hydrate plugs, which can block pipelines. They work by either altering the thermo-dynamic equilibrium (shifting the freezing curve to lower temperatures) or by delaying the nucleation and growth of hydrate crystals (kinetics).
Hydration kinetics – It is the study of the rate, mechanism, and speed at which a material (normally cement) absorbs water and reacts to form hydrated products. It defines the time-dependent progression of hydration, frequently measured by heat release or the degree of reaction (alpha), which controls material hardening, microstructural development, and mechanical strength over time.
Hydration number – It is the average number of water molecules intimately associated with or strongly bound to a single ion, solute molecule, or gas molecule in a solution or hydrate phase. It represents the coordination shell of water around a solute, affecting viscosity and ion transport. It is the number of water molecules which are bonded to a metal ion, or in clathrate hydrates, the number of water molecules per unit cell. It measures the degree of hydration, dictating properties like ion mobility, activity coefficients, and osmotic pressure. For ions, it represents the first coordination shell, where cations attract the oxygen in water, and anions attract the hydrogen. In the context of gas, it is the number of water molecules per unit cell. It is determined using spectroscopic techniques, scattering techniques, or through thermodynamic properties.
Hydration process – It is the exothermic chemical reaction between cement particles and water which transforms the cement paste from a plastic state into a hard, durable, and solid matrix. This process involves dissolution, hydration, and crystallization, releasing substantial heat while producing calcium silicate hydrates (CSH) which provide strength.
Hydration products – These are the new solid compounds, mainly calcium silicate hydrate (C-S-H gel) and calcium hydroxide (CH) formed when cement reacts with water. These products are the binding agents which fill gaps between aggregates, determining concrete’s strength, setting, hardness, and durability.
Hydration reaction – It is a chemical reaction in which a substance combines with water.
Hydration resistance – It is the degree to which a refractory material resists chemical combination with water. This resistance is measured by the test method as specified in the standards.
Hydration shell – It is a structured, dynamic layer of water molecules surrounding dissolved ions, polar molecules, or charged surfaces, formed by strong ion-dipole interactions. It acts as a stabilizing, protective, or repulsive barrier, dictating solubility, molecular mobility, protein function, and interfacial forces.
Hydration system – It is a portable and ergonomic mechanism designed to store and supply water, facilitating adequate hydration for individuals, particularly during physical exertion in extreme environments. This system aims to provide cooled drinking water to prevent heat-related injuries and improve water consumption.
Hydration tendency – It is the tendency of a refractory raw material or product to combine with water when exposed to moist air or steam under controlled test conditions.
Hydraulic – It means pertaining to or using water, oil or other liquids.
Hydraulic accumulator – It is a pressure vessel which stores incompressible hydraulic fluid under pressure, acting as a rechargeable energy source (similar to a battery) for hydraulic systems. It uses a compressed gas (usually nitrogen), weight, or spring to store potential energy, enabling it to compensate for leakage, dampen pressure pulsations, and supply rapid, supplementary fluid flow during high-demand periods.
Hydraulic actuators – These actuators work using essentially the same principal as pneumatic actuators, but the design is usually altered. Instead of a flexible chamber, there is a sealed sliding piston. Also, instead of using a spring as the opposing force, hydraulic fluid is contained on both sides of the piston. The differential pressure across the area of the piston head determines the net force. Hydraulic actuators on the other hand use an incompressible fluid, so the response time is essentially instantaneous. Hydraulic actuators offer the advantages of being small and yet still providing immense force. Draw-backs of hydraulic actuators are mainly the high capital cost and difficulty in maintaining them.
Hydraulic aperture – In rock mechanics and hydrogeology, it is an inferred measurement of a fracture’s void space which defines its fluid-carrying capacity. It is typically derived from fluid flow tests rather than direct physical measurement, representing the equivalent, ideal smooth-walled opening which produces the same flow rate as a real, rough-walled, and tortuous fracture.
Hydraulically bound mixture – It is a construction material composed of aggregate, water, and a hydraulic binder (like cement, lime, or slag) which sets through hydration. It is used for pavement base, sub-base, and capping layers, providing a stiff, durable, and low-strength solid matrix that resists heavy loading.
Hydraulic bond – It is the bond formed by the chemical reaction of specific solid particles with water to produce setting and hardening at ambient temperature.
Hydraulic bulge test – It is a materials testing method used to determine the forming properties of sheet metal. It involves clamping a sheet metal specimen and subjecting it to increasing hydraulic pressure, causing it to bulge until it ruptures. This test provides valuable data on the material’s flow curve, which is essential for understanding its behavior during forming processes.
Hydraulic cement – This cement has the ability to set in the presence of water. Hydraulic cements set and become adhesive through a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates which are not very water-soluble. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack.
Hydraulic-circuit diagrams – These diagrams are complete drawings of a hydraulic circuit. Included in the diagrams is a description, a sequence of operations, notes, and a components list. Accurate diagrams are essential to the designer, the people who build the machine, and the people who maintain the hydraulic system. There are four types of hydraulic-circuit diagrams. They are block, cutaway, pictorial, and graphical. These diagrams show (i) the components and how they will interact, (ii) how to connect the components and (iii) how the system works and what each component is doing.
Hydraulic components – These are engineered, interconnected parts within a fluid power system which generate, control, or transmit pressurized fluid to actuate mechanical movement. Key components, including pumps, actuators, valves, reservoirs, and piping, are designed to manage force and motion in heavy-duty applications, normally utilizing hydraulic oil.
Hydraulic construction – It refers to the projects designed to manage, control, and utilize water resources, involving the planning, design, and implementation of submerged or partially submerged structures. These constructions manage flow for purposes like energy generation, irrigation, and flood protection, incorporating geotechnical, structural, and hydrological factors.
Hydraulic control – It is the use of pressurized fluid (normally oil) to transmit, multiply, and regulate force and motion in machinery. It involves controlling flow, pressure, and direction through valves to operate actuators, enabling precise, high-power, and frequently automated movement in applications like construction equipment and industrial machinery.
Hydraulic conveying – Moving bulk materials along pipes or channels (troughs) in a stream of water is called ‘hydraulic conveying’. The mixture of materials and water is termed as pulp. Pump is used for conveying of pulp through pipe under pressure. In channels the conveying takes place down the inclination due to gravity. A hydraulic conveying system normally consists of a mixer where the material and water are mixed to form the requisite pulp. Depending on starting size of the bulk material, the materials can have to be crushed / ground in a crushing plant and screening facility. The prepared pulp is then pumped by a suitable pumping and piping system. In certain installation a suitable recovery system can be incorporated at the delivery end for dewatering the material. The most important consideration in a hydraulic conveying system is that the material is not to get settled and choke the pipeline. Hydraulic conveyors are used in several industries, mining operations and construction works. Some of the popular uses are to dispose ash and slag from boiler rooms, deliver materials from mines and sand and water to fill up used mines, to remove slag from concentration plants, to quench, granulate and convey furnace slag to disposal points, to move earth and sand in large construction projects and for land filling etc.
Hydraulic conveyor – It is a conveyor system utilizing hydraulic power for material movement, demanding inspections for fluid levels, leaks, and overall functionality to prevent system failure.
Hydraulic cylinder – It is a mechanical device which converts hydraulic energy into linear mechanical motion. It uses pressurized hydraulic fluid (typically oil) to move a piston, which in turn drives a rod and generates force in a straight line. Essentially, it is an actuator which transforms fluid pressure into a pushing or pulling force.
Hydraulic design – It is the application of fluid mechanics principles to calculate, analyze, and size systems which collect, control, and transport liquids, mainly water, or power machinery through pressurized oil. It focuses on optimizing flow efficiency, pressure management, and structural integrity for infrastructure like pipes, channels, and hydraulic machinery.
Hydraulic diameter (Dh) – It is a term used to calculate fluid flow and pressure drop in non-circular conduits by treating them as equivalent circular pipes. It is defined as four times the cross-sectional area (A) divided by the wetted perimeter (P), formulated as Dh = 4A/P.
Hydraulic disturbance – It refers to the transient, involuntary instability caused in running units when other units in the same shared waterway system rapidly change their load or trip. This creates fluctuating water levels, head, and discharge, leading to potential unit over-current, power oscillation, and reduced stability. Hydraulic disturbances can damage and / or fail any or all the pump components. Hydraulic disturbances are cavitation, low flow suction recirculation, low flow discharge recirculation and liquid vapourization. Hydraulic disturbances are eliminated by proper venting and purging of the pump, and operating in the stability range of the pump (the equipment reliability operating envelope, EROE).
Hydraulic drive – It is a system which converts mechanical energy (from an electric motor or engine) into pressurized fluid energy through a pump, which is then transferred through valves and pipes to actuators (cylinders or motors) to generate precise linear or rotary motion. These systems operate based on Pascal’s principle to deliver high force, torque, and power density.
Hydraulic drive press – It is an industrial machine which utilizes a pressurized fluid (typically oil) within a closed system to actuate a cylinder, generating substantial compressive force for forming, assembling, or shearing materials. Operating on Pascal’s law, it converts mechanical power from a pump into hydraulic energy to move a ram, offering high force, versatility, and precise control.
Hydraulic drive system – It is a system which transmits power by using pressurized hydraulic fluid to drive machinery. It utilizes Pascal’s principle to amplify force, enabling heavy machinery to perform tasks like lifting and tilting. These systems are composed of a pump (the generator), control valves and piping, and an actuator (motor or cylinder).
Hydraulic direct drive systems – These systems consist of a hydraulic pump, control valves, and a motor which converts pressurized fluid directly into rotary or linear motion, eliminating intermediate mechanical transmissions like gears or belts. They offer high power density, superior shock load resistance, and flexible mounting.
Hydraulic edger adjusting system – The width of the strip from its head to its tail is controlled by this system. The quick dynamic response of this system enables the fast corrective movements at the material head and tail for reducing cropping losses and in controlling the width over the length of the strip. Latest generation edgers are fully hydraulic facilities without any additional electro mechanical adjusting systems.
Hydraulic energy – It is the power derived from the potential and kinetic energy of water, typically harnessed by converting water’s flow or fall into mechanical energy through turbines, and then into electrical energy. It is a renewable, sustainable energy source frequently used in hydro-electric dams, run-of-river systems, and tidal flows.
Hydraulic engineering – It is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the movement of the fluids. Hydraulic engineering is the application of the principles of fluid mechanics to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water.
Hydraulic fill – It is a technique for land reclamation, dam construction, or mining backfill where soil (normally sand) is dredged from a water source, transported as a slurry through pipelines, and deposited at a site to raise land elevation or fill voids. It uses water to transport and place sediment, relying on gravity and controlled water flow to drain surplus water and settle the material.
Hydraulic filling – It is a process which uses a water-based slurry to transport and deposit materials (typically sand or tailings) through pipelines to raise land levels, create new land, or fill underground mining voids. The technique involves dredging material, pumping it as a mixture, and allowing it to settle, with surplus water drained away.
Hydraulic fluid – Hydraulics is a technology for transferring of potential or kinetic energy (pressure and movements) using a fluid as the energy carrier. The fluids which are used for this purpose are known as hydraulic fluids. Hydraulic fluid is the medium by which power is transferred in hydraulic machinery. The hydraulic fluid frequently being referred as ‘hydraulic oil’, creates volume flow between pump and hydrostatic motor, and is in contact with all the components in a hydraulic system. Hydraulic fluid is a complex liquid which has to serve several different purposes and possess several different characteristics. Fully formulated hydraulic fluids consist of a blend of a base fluid and an additive package. Hydraulic fluid plays a very important role in the operation of machines. Common hydraulic fluids are based on mineral oil or water. Hydraulic systems work very efficiently if the hydraulic fluid used has zero compressibility.
Hydraulic forming – It is also called Hydro-forming. It is a specialized cold metal-forming process which utilizes high-pressure hydraulic fluid (liquid) to force a metal workpiece, typically sheet metal or a tube, into a desired, complex shape inside a die. Unlike traditional stamping which uses a rigid male punch and female die, hydric-forming replaces one of these tools with a rubber bladder or direct, high-pressure fluid, resulting in more even pressure distribution, fewer wrinkles, reduced material thinning, and the ability to create complex geometries with higher strength-to-weight ratios.
Hydraulic fracture growth – It is the process of expanding fractures in subsurface rock formations by injecting high-pressure fluids, overcoming the in-situ stress to create, extend, and propagate conductive cracks. It aims to maximize stimulation, typically growing vertically perpendicular to the minimum stress, guided by rock mechanics and fluid viscosity.
Hydraulic fracturing – It is also called hydraulic fracking. It is a well-stimulation technique used to increase oil and natural gas flow from low-permeability reservoirs (e.g., shale, tight sand) by creating artificial fissures. It involves injecting pressurized fluid (water, sand, and additives) down a wellbore to crack rock and using proppants to keep them open.
Hydraulic fracturing design – It is a process which optimizes fluid injection, proppant selection, and pumping schedules to create, propagate, and maintain fractures in rock, maximizing hydrocarbon flow from low-permeability reservoirs. It involves modeling fracture geometry (height, length, width) and conductivity based on geo-mechanical data.
Hydraulic fracturing model – It is a mathematical, numerical, or computational representation used to simulate the initiation, growth, and propagation of fractures in subsurface rock formations caused by high-pressure fluid injection. It serves as a, ‘virtual laboratory’ which couples geo-mechanical, hydraulic, and thermal processes to predict fracture geometry (length, height, width), conductivity, and proppant placement, allowing for the optimization of well stimulation and production.
Hydraulic gap control – It is done by a controller which receives a gap reference and measures the gap coming from position encoders placed in the hydraulic cylinder and produces the servo-valve command which indeed controls the oil mass flow generating the movement of the cylinder. Obviously, the measured gap can be significantly different from the physical gap of the stand because of the stand elastic stretch. The hydraulic gap control is the second module in the gap control, controlling the gap between the two work rolls. The hydraulic gap control uses the higher-level set points as roll gap reference values. Measurements from position transducers on the cylinders and the current compensation are used to calculate the true roll gap. The hydraulic gap control is position controlled and uses the reference and the true gap to control the strip thickness. To close or widen the gap, the hydraulic gap control steers the servo valves for the hydraulic cylinders. The opening or closing of the valves increase or decrease the rolling force. The signal from the load cells gives a good approximation of the size of the rolling force and is used in the hydraulic gap control to calculate the gap compensation. There are two position transducers on each of the hydraulic cylinders which are measuring the cylinder stroke. The hydraulic gap control is implemented as a proportional integral (PI) controller. Both the reference and the control signal are ramped and have an upper limit. This means that the signal has a maximum value and that the rate of increase is limited. This is done to avoid heavy strains on the mechanical parts.
Hydraulic gates – These are movable structures, typically steel or timber plates, designed to control, regulate, or stop the flow of water in dams, canals, spillways, and locks. They function as important flow-regulation devices, utilizing vertical lifting, sliding, or radial (hinged) motion to manage water levels and pressure, frequently powered by hydraulic cylinders, pumps, or hoists.
Hydraulic grade line – It is a graphical representation of the sum of pressure head [P/(d x g)] and elevation head (z) along a fluid flow system. It represents the potential energy available, specifically the height water would rise in a series of piezometer tubes. It sits one velocity head (V-square/2g) below the energy grade line.
Hydraulic gradient (i) – It is the dimensionless ratio representing the loss of total hydraulic head (h) over a specific flow length (L) in porous media or pipes, expressed as ‘I = L/dh’. It defines the driving force for fluid movement, indicating the direction and velocity of groundwater flow or seepage through soil and rock.
Hydraulic hammer – It is a gravity-drop forging hammer which uses hydraulic pressure to lift the hammer between strokes.
Hydraulic hoists – Hydraulic hoists are powered by hydraulic motors. When equipped with a chain as the lifting mechanism, they are called hydraulic chain hoists. Likewise, when equipped with a wire rope as the lifting medium, they are called hydraulic wire rope hoists.
Hydraulic horsepower – It is the measure of power transferred through a fluid system, defined as the energy per unit of time (flow rate multiplied by pressure) delivered by a pump. It is the power needed to lift a volume of liquid through a height in a specified time, calculated based on the work done in raising the liquid, assuming 100 % pumping efficiency. It is expressed in horsepower (HP) and can be derived from the flow rate and head developed by the pump.
Hydraulic hybrid vehicle – It is a vehicle drive-train which combines a main engine (normally diesel or gasoline) with a hydraulic propulsion system, high-pressure accumulators, pump / motors, and fluid reservoirs, to improve efficiency. It converts mechanical engine power into pressurized fluid, storing braking energy in accumulators (up to 70 % to 80 % efficiency) to aid acceleration.
Hydraulic installation – It is a designed, closed network of components, including pipes, hoses, pumps, valves, and actuators, which uses incompressible, pressurized fluid (typically oil) to transmit power, generate force, and control motion in machinery or structures. It is a practical application of Pascal’s Law, allowing for high power density and precise control in construction, manufacturing, and automotive applications.
Hydraulic jack – It is a mechanical device, operating on Pascal’s principle, which uses incompressible fluid (normally oil) within a cylinder to lift heavy loads by converting low-input force into high-output lifting power. It consists of a pump plunger, reservoir, and cylinder, allowing for controlled, vertical, or horizontal movement.
Hydraulic jump – It is an abrupt, turbulent transition in open-channel flow where water rapidly changes from supercritical (high-velocity, low-depth) to subcritical (low-velocity, high-depth) flow. It acts as a primary energy dissipator, reducing kinetic energy by over 85 %, preventing erosion downstream of spillways and dams.
Hydraulics laboratory procedures – These procedures involve operating water flow apparatus (benches, flumes, pipes) to measure parameters like pressure, discharge, and velocity. Key steps include checking equipment calibration, purging air, starting the pump to stabilize flow, recording manometer / sensor readings, and collecting volumetric data to calculate flow rates, ensuring safety precautions are followed.
Hydraulic loss – It involves calculating or measuring energy dissipation in fluid systems, mainly caused by friction (viscous dissipation) and turbulence. It is calculated by determining pressure drops, using methods like the Darcy-Weisbach equation for pipes or analyzing local losses (bends, valves) through energy, pressure, and velocity parameters.
Hydraulic machinery – It constitutes systems which utilize pressurized, incompressible fluids (typically oil or water) to transmit, control, and amplify force to perform mechanical work. Operating mainly on Pascal’s Law, these systems use pumps to pressurize fluid, transmitting it through pipes to actuators, motors, and cylinders for applications like construction, lifting, and braking.
Hydraulic machines – These are engineering systems which utilize pressurized, incompressible liquid (typically oil) to transmit power, generate motion, and perform work, based on Pascal’s law. They consist of components like pumps, cylinders, and motors to convert fluid energy into high-force, precise mechanical movement.
Hydraulic-mechanical press brake – It is a mechanical press brake which uses hydraulic cylinders attached to mechanical linkages to power the ram through its working stroke.
Hydraulic mining – It is a method which uses high-pressure water jets, delivered through nozzles called ‘monitors’ or ‘giants,’, to dislodge rock, sediment, or ore from banks, cliffs, or underground seams. It breaks up, transports, and processes material, such as gold-bearing gravel or coal, by turning it into a slurry, which is frequently processed in sluice boxes.
Hydraulic model – It is a physical or, very frequently, a mathematical / numerical simulation used to analyze and predict the behaviour of liquid (normally water) flowing through pipes, channels, or across terrain. These models use physical attributes, hydraulic principles, and topographical data to simulate real-world scenarios for design, analysis, and management.
Hydraulic motor – It is a mechanical actuator which converts hydraulic energy, pressurized fluid (flow and pressure, into continuous rotary mechanical motion (torque and speed). Functioning as the reverse of a hydraulic pump, it is normally used in heavy-duty machinery for high torque, variable speed, and robust motion control, such as gear, vane, and piston types.
Hydraulic motor actuator (operator) – It is a device by which rotation of an hydraulically powered motor is converted into mechanical motion.
Hydraulic oil – It is a specialized, normally non-compressible, low-viscosity fluid used as the working medium to transmit power in hydraulic machinery and industrial systems. Composed of mineral or synthetic base oils, it acts as a lubricant, coolant, and sealant, protecting components from corrosion and wear.
Hydraulic parameters – These are quantitative measures, including flow rate, pressure, viscosity, velocity, and fluid density, which define, analyze, and control the behaviour of fluids (typically water or oil) within systems like pipes, channels, or porous media. These parameters, such as hydraulic conductivity and head, are important for assessing structural stability, pump performance, and flow capacity.
Hydraulic permeability – It is a material property defining the ease with which a porous medium (soil, rock, or membrane) allows fluids to flow through its interconnected pores under a pressure gradient. It is an important, non-linear parameter for Darcy’s law, representing flow rate per unit area.
Hydraulic power – It is the technology of generating, controlling, and transmitting energy using pressurized, incompressible liquids (typically oil or water) within a closed system. It converts mechanical energy from a prime mover (motor / engine) into fluid power through a pump, which is then delivered to actuators (cylinders or motors) to perform work.
Hydraulic power unit – It is a device to create kinetic energy within a hydraulic system. It normally comprises a motor (electric / air/ engine powered), a storage tank, filters, regulators, directional valves, and gauges etc. to power one or multiple valve actuators.
Hydraulic press – It is a press in which fluid pressure is used to actuate and control the ram. It utilizes Pascal’s principle to generate high compressive force by using a pressurized, confined fluid (normally oil) within a hydraulic cylinder. It acts as a force multiplier, allowing small input forces on a small piston to produce massive output forces on a larger piston for shaping, moulding, or compacting materials. Hydraulic presses are used for both open- and closed-die forging.
Hydraulic press brake – It is a machine tool used for bending sheet metal and plate material. It features a hydraulic system which applies force to a punch, which in turn pushes the material against a die to form the desired bend. Hydraulic press brakes are normally used in metalworking and fabrication industries for tasks such as forming metal brackets, casings, enclosures, and more. They offer precise control over the bending process and are capable of creating accurate and repeatable bends in various materials.
hydraulic press drives – These drives are based on the motion of a hydraulic piston guided in a cylinder. Two types of drive systems are used on hydraulic presses namely direct drive and accumulator drive. Direct drive presses for closed-die forging normally have hydraulic oil as the working medium. At the start of the downstroke, the return cylinders are vented, allowing the ram / slide assembly to fall by gravity. The reservoir used to fill the cylinder as the ram is withdrawn can be pressurized to improve hydraulic flow characteristics, but this is not mandatory. When the ram contacts the work-piece, the pilot-operated check valve between the ram cylinder and the reservoir closes, and the pump builds up pressure in the ram cylinder. Modern control systems are capable of very smooth transitions from the advance mode to the forging mode. Accumulator-drive presses can operate at faster speeds than direct-drive presses. The faster press speed permits rapid working of materials, reduces the contact time between the tool and work-piece, and maximizes the quantity of work performed between reheats. Pressure buildup is related to workpiece resistance. Modern pumps can fully load in 100 milli-seconds, not much different from the opening time for large valves. In both direct and accumulator drives, as the pressure builds up and the working medium is compressed, a certain slowdown in penetration rate occurs. This slowdown is larger in direct oil driven presses, mainly because oil is more compressible than a water emulsion. The approach and initial deformation speeds are higher in accumulator-driven presses.
Hydraulic pressure – It is the force per unit area (P = F/A) exerted by a confined liquid (oil or water) to transmit energy, lift heavy loads, or drive machinery. Based on Pascal’s law, this pressure acts equally in all directions, allowing small input forces to generate much larger output forces.
Hydraulic pump – It is a mechanical source of power which converts mechanical power into hydraulic energy (hydrostatic energy i.e., flow, pressure). Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. They generate flow with enough power to overcome pressure induced by a load at the pump outlet. When a hydraulic pump operates, it creates a vacuum at the pump inlet, which forces liquid from the reservoir into the inlet line to the pump and by mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system. Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement (flow through the pump per rotation of the pump) cannot be adjusted, or variable displacement pumps, which have a more complicated construction that allows the displacement to be adjusted. Hydrodynamic pumps are more frequent in day-to-day life. Hydrostatic pumps of various types all work on the principle of Pascal’s law.
Hydraulic pump unit – It is a system which converts mechanical power (normally from an electric motor or engine) into hydraulic fluid power. It acts as the heart of a hydraulic system, generating flow and pressure to move actuators like cylinders or motors.
Hydraulic radius (Rh) – It is an important parameter in fluid mechanics defined as the ratio of the cross-sectional area of flow (A) to the wetted perimeter (Pw), expressed as ‘Rh = A/Pw’. It measures channel efficiency, where a higher value indicates less frictional energy loss and higher flow capacity.
Hydraulic ram – It is a self-acting, cyclic water pump which uses the kinetic energy of falling water (water hammer effect) to lift a small portion of that water to a higher elevation, needing no external power. It operates through a cycle of high-velocity flow, pressure buildup, and valve manipulation.
Hydraulic ram pump – It is a water pump powered by hydropower. It takes in water at relatively low pressure and high flow-rate and outputs water at a higher hydraulic-head and lower flow-rate. The device uses the water hammer effect to develop pressure that lifts a portion of the input water that powers the pump to a point higher than where the water started. The hydraulic ram is sometimes used in remote areas, where there is both a source of low-head hydropower, and a need for pumping water to a destination higher in elevation than the source. In this situation, the ram is frequently useful, since it requires no outside source of power other than the kinetic energy of flowing water.
Hydraulic reservoir – It is a container for holding the fluid required to supply the system, including a reserve to cover any losses from minor leakage and evaporation. The reservoir is normally designed to provide space for fluid expansion, permit air entrained in the fluid to escape, and to help cool the fluid. Hydraulic reservoirs are either vented to the atmosphere or closed to the atmosphere and pressurized. Fluid flows from the reservoir to the pump, where it is forced through the system and eventually returned to the reservoir. The reservoir not only supplies the operating needs of the system, but it also replenishes fluid lost through leakage. Furthermore, the reservoir serves as an overflow basin for excess fluid forced out of the system by thermal expansion (the increase of fluid volume caused by temperature changes), the accumulators, and by piston and rod displacement.
Hydraulic residence time (HRT) – It is also called hydraulic retention time. It is the average duration a fluid (water or wastewater) stays within a reactor, tank, or treatment system. It is calculated by dividing the tank volume (V) by the flow rate (Q) i.e., ‘HRT = V/Q’, and it is important for ensuring sufficient time for physical, chemical, or biological treatment processes.
Hydraulic retention time – It is the average time in the aeration basin equivalent to the volume of the basin divided by the average flow and expressed as hours. The hydraulic retention time is required to be sufficiently long to remove the prerequisite biological oxygen demand (BOD) and is dependent on the type of the biological treatment system. It can range from 0.5 hours to 120 hours. The lower the hydraulic retention time the quicker the wastewater reaches the outlet.
Hydraulics – It is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids.
Hydraulic seats – It consists that the movement of the seats in a valve is controlled by using water, oil or other liquids under pressure.
Hydraulic shear -It is a shear in which the cross-head is actuated by hydraulic cylinders.
Hydraulic simulation – It is a computer-based, computational process which models the behaviour of fluids (water, oil, etc.) within systems like pipe networks, machinery, or natural water bodies. By creating a ‘digital twin’ of a physical system, engineers can test, predict, and optimize performance parameters like pressure, flow, and velocity to improve safety and design efficiency.
Hydraulics optimization – It is the systematic process of adjusting system variables, such as flow rate, pressure, nozzle sizes (total flow area, TFA), or fluid rheology, to achieve maximum performance efficiency, such as maximum cleaning power in drilling or improved energy conversion in machinery. It minimizes energy losses to improve safety, reduce costs, and maximize efficiency within operational constraints.
Hydraulic structures – These are specialized constructions, either fully or partially submerged, designed to control, manage, and utilize water resources. They alter natural water flow for purposes like storage (dams, reservoirs), conveyance (canals, pipes), flood control (spillways, floodwalls), or energy generation (hydro-electric turbines).
Hydraulic system – It is one of the drive systems which are being used for the control of machinery and equipment. Typically, the fluid used in a hydraulic system is an incompressible liquid such as mineral based hydraulic oil. Pressure is applied by a piston to fluid in a cylinder, causing the fluid to press on another piston which delivers energy to a load. If the areas of the two pistons are different, then the force applied to the first piston is different from the force exerted by the second piston. This creates a mechanical advantage. The hydraulic system works on the principle of Pascal’s law which says that the pressure in an enclosed fluid is uniform in all the directions. The force given by fluid is given by the multiplication of pressure and area of cross section. As the pressure is same in all the direction, the smaller piston feels a smaller force and a large piston feels a large force. Hence, a large force can be generated with smaller force input by using hydraulic systems.
Hydraulic take-up – It is a tensioning device in a conveyor system which uses hydraulic pressure to maintain belt tension, requiring regular checks for fluid levels and system integrity to ensure proper tension control.
Hydraulic torque controller – In the hot strip mill, the hydraulic torque controller is in charge of controlling the torque generated by the looper.
Hydraulic torque converter – It is a hydrodynamic fluid coupling used in automatic transmissions to transmit rotational power from an engine to the drivetrain, acting as a ‘fluid clutch’. It multiplies engine torque during acceleration using three main components, impeller, turbine, and stator, allowing smooth, variable power transfer.
Hydraulic transportation – It is the method of moving solid materials, such as coal, ore, or waste, over long distances through pipelines by suspending them in a liquid medium, normally water. This two-phase, slurry-based system relies on optimized flow velocities to maintain suspension, prevent settling, and manage pipe wear.
Hydraulic turbine – It is also called hydro turbine. It is a rotary mechanical device which converts the potential energy (head) and kinetic energy of moving water into mechanical energy, which is typically used to drive a generator for electricity production. They are the ‘heart’ of hydroelectric power plants. Hydro turbines operate by using water flow to spin a rotor, called a runner, which has blades, vanes, or buckets.
Hydride – It is formally the anion of hydrogen (H-), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and more frequently in the past) been applied to all compounds containing covalently bound H-atoms. In this broad and potentially archaic sense, water (H2O) is a hydride of oxygen, and ammonia (NH3) is a hydride of nitrogen etc. In covalent compounds, it implies hydrogen is attached to a less electro-negative element.
Hydride decomposition – It is the process of breaking down metal hydrides (MHx) into metal and hydrogen gas (H) to release stored hydrogen or produce fine metal powders, typically achieved through thermal decomposition (heating) or electro-chemical methods. It is a critical, frequently energy-intensive, endothermic reaction used for energy storage, powder metallurgy, and reducing hydrogen embrittlement.
Hydride formation – It is the chemical reaction of hydrogen with metals, alloys, or less electro-negative elements to form compounds (MHx), frequently a reversible gas-solid reaction used for hydrogen storage. This process involves hydrogen absorption into a metal lattice (normally forming alpha-solid solution and beta-hydride phases), causing volumetric expansion, brittleness, and potential hydrogen-induced cracking.
Hydride phase – It is a distinct, high-hydrogen-concentration, solid-solution phase (beta-phase) which forms within a metal matrix (alpha-phase) once the hydrogen solubility limit is exceeded. Characterized by a different crystal structure and larger unit cell volume, it forms through diffusion and typically causes embrittlement, frequently found as precipitates like gamma or delta in zirconium (Zr) or titanium (Ti) alloys. This phase is normally locally because of some special circumstance.
Hydride powder – It is a powder produced by the removal of hydrogen from a metal hydride.
Hydride process – It consists of the hydrogenation of such reactive metals as titanium and zirconium, followed by comminution of the brittle compound and vacuum treatment to remove the hydrogen from the powder.
Hydride tank – It is a specialized engineering pressure vessel designed for solid-state hydrogen storage, holding metal hydride alloys which absorb and desorb hydrogen through chemical reactions rather than high-pressure compression. These tanks incorporate thermal management systems to manage the heat produced during absorption (charging) and needed for desorption (discharging), frequently utilizing cylindrical or planar structures for efficient packing.
Hydride transfer mechanism – It is a fundamental chemical process, where a hydrogen atom, along with two electrons (a H- ion), is transferred from a donor molecule to an acceptor. It is important in reducing carbonyl compounds to alcohols, catalyzing redox reactions, and in metal-hydride systems for energy storage and hydrogenation.
Hydriding kinetics – It refers to the study of the time-dependent rate and mechanisms associated with the absorption of hydrogen by metals or alloys to form metal hydrides. It describes how quickly a material can uptake hydrogen, focusing on the speed, controlling mechanisms (like diffusion or surface reaction), and factors influencing the rate such as temperature, pressure, and particle morphology.
Hydroamination – It is the direct, atom-economical addition of an amine (nitrogen-hydrogen, N-H) bond across a carbon-carbon multiple bond (alkene or alkyne) to form amines or enamines, typically using a metal or acid catalyst. It is a key green process for producing substituted amines and heterocyclic compounds for industrial applications.
Hydro-blast process – It is a process for descaling of steel. In this process sand is mixed with water and propelled by the water pressure.
Hydro-carbon – It is a chemical compound of hydrogen and carbon.
Hydro-carbon backbone – It is the fundamental, continuous chain or ring of carbon atoms bonded to hydrogen atoms which forms the structural framework of organic molecules, polymers, and fossil fuels. It defines the molecule’s core shape (linear, branched, or cyclic) and determines its physical properties like boiling point and reactivity.
Hydrocarbon-based grease – It is a solid-to-semifluid lubricant engineered by dispersing a thickener (typically metal soap) within a petroleum-derived or synthetic hydrocarbon base oil. These greases provide necessary lubrication for machinery, bearings, and vacuum systems, offering high surface tension which resists migration compared to silicones.
Hydrocarbon-bearing zone – It is a specific interval of sub-surface porous rock, such as sandstone, limestone, or shale, which contains substantial, measurable volumes of oil, natural gas, or both. Identification of these zones focuses on quantifying whether the hydrocarbon content is present in sufficient quantities, is economically recoverable, and has sufficient flow capability (permeability) to be produced.
Hydrocarbon chain – It is an organic molecular backbone composed of carbon atoms covalently bonded in sequence (linear, branched, or cyclic) with hydrogen atoms attached, acting as the foundation for fuels, plastics, and lubricants. Engineered to be either saturated (single bonds) or unsaturated (double / triple bonds), they are classified by chain structure, alkanes, alkenes, or alkynes, determining their reactivity and physical properties like viscosity and boiling point.
Hydrocarbon generation – It is the geological process where organic matter (kerogen) in sedimentary source rocks is transformed into oil and natural gas through thermal degradation (maturation) driven by burial, pressure, and heat (diagenesis, catagenesis, metagenesis) over geological time. This process is necessary for oil and gas reservoir formation. Hydrocarbon liquids – Thess are organic compounds composed solely of carbon and hydrogen which exist in a liquid state under processing, storage, or transport conditions. Mainly derived from crude oil or processed natural gas, these high-energy-density substances include crude oil, condensate, naphtha, and liquid fractions like propane / butane.
Hydrocarbon liquid phase – It is a physically distinct, condensed state of matter composed of organic compounds (crude oil, condensate, or petroleum fractions) which coexists with vapour or aqueous phases. Iit is defined by specific pressure-temperature (P-T) conditions, such as being below the bubble point, and is identified by parameters like API (American Petroleum Institute) gravity, gas-liquid ratio (GLR), and C7+ content.
Hydrocarbon loss – It refers to the reduction in volume or mass of desirable hydrocarbon products (oil, gas, condensate) during exploration, production, processing, or transportation. It is frequently analyzed through the lens of phase behaviour, which describes how liquids flash into gases or gases condense into liquids because of the changes in pressure and temperature (P/T).
Hydrocarbon medium – It refers to a fluid, liquid or gas, composed mainly of organic compounds containing only carbon (C) and hydrogen (H) atoms. These media are necessary in process engineering for their ability to serve as solvents, reaction environments, or fuels.
Hydrocarbon mixture – It is a complex blend of different hydrogen-carbon compounds (alkanes, alkenes, cycloalkanes, aromatics) derived mainly from crude oil or natural gas. These mixtures are defined by their composition, physical properties (like boiling points), and thermodynamic behaviour, such as phase transformations (vapour-liquid coexistence) under varying pressure and temperature conditions.
Hydrocarbon pore volume (HCPV) – It is the volume of oil or gas contained within the pore spaces of a reservoir rock at in-situ conditions. It is determined using geological and petrophysical parameters such as reservoir area, average thickness, porosity, and water saturation. It is calculated as the product of bulk rock volume, porosity, and net-to-gross ratio, adjusted for water saturation [HCPV = A x h x phi x (1-Sw)]. It represents the total hydrocarbon volume in place before recovery factors.
Hydrocarbon processing plants – These are industrial facilities which refine and convert raw crude oil and natural gas into fuels, lubricants, and petrochemical feedstocks (naphtha, diesel, gasoline). They utilize complex, continuous processes like distillation, cracking, and treating to improve efficiency and safety.
Hydrocarbon refining – It is the engineering process of transforming raw crude oil into usable, higher-value products (gasoline, diesel, jet fuel) through physical separation, chemical conversion, and treatment. It involves manipulating hydrocarbon molecules using heat, pressure, and catalysts to meet quality standards and remove impurities like sulphur.
Hydrocarbon release – It is the unintended escape of gaseous, liquid, or mist hydrocarbons (compounds of hydrogen and carbon, such as oil or natural gas) from pressurized systems, pipelines, or processing equipment. Occurring because of the corrosion, equipment failure, or human error, these releases pose substantial risks of fire, explosion, or environmental damage.
Hydrocarbon resins – These are low molecular weight (MW), thermoplastic polymers (typically below 2,000 MW) produced through cationic polymerization of coal-tar, petroleum, or terpene feedstock (C5 aliphatic, C9 aromatic, or C5 / C9 copolymers). Engineered for adhesive, paint, rubber, and coating applications, they act as tackifiers, modifiers, and binders to improve performance, processability, and tackiness.
Hydrocarbon separation – It is the process of isolating specific hydrocarbon types (e.g., olefins from paraffins, methane from natural gas) or fractions from complex mixtures like crude oil or raw gas. It utilizes techniques such as distillation, adsorption, and membrane filtration to purify, refine, or divide components based on physical / chemical properties.
Hydrocarbon solvents – These are liquid organic compounds derived from petroleum or natural gas, consisting exclusively of carbon and hydrogen atoms. Engineered for industrial applications, they typically contain C5 – C20 molecules, with boiling points ranging from 35 deg C to 370 deg C. These are widely used for cleaning, degreasing, and dissolving waxes, resins, and oils.
Hydrocarbon stream – It is a flowing mixture of hydrogen and carbon compounds (alkanes, aromatics) combined with impurities like water, salts, or acid gases, derived from oil / gas extraction or processing. These streams are characterized by their, phase (gas, liquid, or multi-phase), composition, and pressure-temperature behaviour.
Hydrochar – It is a carbon-rich, solid material produced by the hydrothermal carbonization (HTC) of wet biomass (sewage sludge, agricultural waste) in a pressurized, subcritical water environment (180 deg C to 350 deg C). Engineered for waste-to-energy conversion, it boasts higher energy density, lower ash content, and superior surface functionality (carboxyl / hydroxyl groups) compared to raw feedstock, making it ideal for fuel, soil amendment, and contaminant adsorption.
Hydrochloric acid – It is also known as muriatic acid or spirits of salt. It is an aqueous solution of hydrogen chloride (HCl). It is a colourless solution with a distinctive pungent smell. It is classified as a strong acid. It is used for pickling of steel. It is an important laboratory reagent and industrial chemical.
Hydrochloric acid corrosion – It is the severe, frequently rapid deterioration of metals (especially carbon steel) caused by exposure to aqueous hydrochloric acid, creating low-pH (below 4.5) conditions. It acts as a reducing acid which breaks down protective passivation layers, resulting in uniform thinning or localized pitting and grooves.
Hydrochlorination – It is the chemical process of adding hydrogen chloride (HCl) to unsaturated organic compounds (alkenes / alkynes) or inorganic materials, normally used to produce vinyl chloride monomer (VCM) for PVC (poly vinyl chloride), or in the manufacturing of silanes. It frequently utilizes catalysts in fluidized bed reactors (FBR) to manage exothermic reactions and improve selectivity.
Hydro-chloro-fluoro-carbons – These are chemical compounds which contain carbon, hydrogen, chlorine, and fluorine. are chemical compounds containing hydrogen, chlorine, fluorine, and carbon, developed as temporary, transitional refrigerants to replace ozone-depleting chloro-fluoro-carbons (CFCs). Engineered for HVAC/R (heating, ventilation, air conditioning and refrigeration) systems, they have lower ozone depletion potential (ODP) than chloro-fluoro-carbons but are still phased out because of the remaining chlorine and high global warming potential (GWP).
Hydro-chloro-fluoro-carbon refrigerants – These are chemical compounds developed as safer, nontoxic, and nonflammable alternatives to earlier refrigerants, but they are being phased down because of their contribution to ozone depletion and high global warming potential.
Hydrocracker – It is a high-pressure refinery unit which uses hydrogen and a dual-functional catalyst (metallic and acidic) to crack heavy, low-value feedstocks (e.g., vacuum gas oil, coker gas oil) into high-value lighter products like gasoline, jet fuel, and diesel. It operates at high temperatures (370 deg C to 540 deg C) and pressures (10 mega-pascals to 20 mega-pascals), simultaneously removing impurities like sulphur and nitrogen.
Hydrocracking – It is a versatile, high-pressure catalytic petroleum refining process that converts heavy, high-molecular-weight feedstocks (like vacuum gas oil) into lighter, high-value products (naphtha, jet fuel, diesel). It combines catalytic cracking and hydrogenation over a dual-functional catalyst (acidic sites for cracking, metal sites for hydrogenation) to break molecular bonds and saturate products, while removing contaminants like sulphur and nitrogen.
Hydrocracking reactions – These are the main sources of C4- hydrocarbons (C1, C2, C3 and C4). The reactions are highly exothermic and consume high amounts of hydrogen. Cracking results in the loss of the reformate yield.
Hydrocyclone – It is a type of cyclonic separator which separates product phases mainly on basis of differences in gravity with aqueous solutions as the primary feed fluid. It is a device which uses centrifugal force generated by a swirling fluid flow to separate particles or droplets from a liquid medium, based on differences in density. It is essentially a conical vessel where a slurry enters tangentially, creating a vortex which separates denser particles (which are forced outward) from lighter ones. As opposed to dry or dust cyclones, which separate solids from gasses, hydrocyclones separate solids or different phase fluids from the bulk fluid. A hydrocyclone comprises a cylindrical shaped feed part with tangential feed, an overflow part with vortex finder, and a conical part with an apex. A cyclone has no moving parts.
Hydro-denitrification – It is also called hydro-denitrogenation. It is a catalytic process used in oil refining to remove nitrogen compounds from hydrocarbon feedstocks. It utilizes hydrogen at high temperatures and pressures to convert organic nitrogen into ammonia (NH3), improving fuel quality, reducing NOx (nitrogen ox-des) emissions, and preventing catalyst poisoning in downstream units. It is a hydrotreating process which involves the removal of nitrogen compounds from crude oil fractions, improving the product’s properties and reducing harmful emissions during combustion.
Hydro-denitrogenation – It is a catalytic hydrotreating process in petroleum refining which removes nitrogen atoms from hydrocarbon feedstocks, converting organic nitrogen compounds into hydrocarbons and ammonia (NH3). It operates under high temperatures (350 deg C to 500 deg C) and high hydrogen pressures, important for reducing NOx (nitrogen oxides) emissions and preventing nitrogen-induced catalyst poisoning downstream. It is necessary for upgrading fuel quality, reducing emissions, and preventing catalyst poisoning in downstream units.
Hydro-deoxygenation – It is a catalytic process which removes oxygen from organic compounds, mainly biomass-derived oils (pyrolysis oil) or lignin, by reacting them with hydrogen to form water. It upgrades low-quality oxygenates into stable, high-energy, hydrocarbon-rich fuels or chemicals, typically operating under high pressure and temperature.
Hydro-desulphurization – It is a catalytic chemical process which removes sulphur from refined petroleum products (gasoline, diesel, jet fuel) by reacting sulphur compounds with hydrogen at high temperatures (300 deg C to 400 deg C) and pressures (3 mega-pascals to 13 mega-pascal). It reduces sulphur to hydrogen sulphide (H2S), lowering toxic SOx emissions, normally using cobalt-molybdenum / aluminum oxide (Co-Mo / Al2O3) or nickel-molybdenum catalysts.
Hydrodynamically developed flow – It occurs when a fluid’s velocity profile becomes invariant with respect to the axial direction (pipe length) after an initial developing entrance region. In this region, the boundary layers merge, the shape of the velocity profile (parabolic for laminar, flatter for turbulent) remains constant, and the shear stress at the wall remains constant.
Hydrodynamic coefficients – These are dimensionless numerical parameters, such as drag (Cd), lift (Cl), and inertia (Ci), used to model, calculate, and predict the fluid-induced forces and moments acting on submerged objects, such as ships, underwater vehicles, or offshore structures. They quantify the interaction between a body and surrounding fluid based on flow conditions, including the Reynolds number and wave action.
hydrodynamic condition – It defines the specific, time-varying environment of a moving fluid (normally liquid) defined by parameters like velocity, pressure, viscosity, and density. It describes how these forces interact with submerged objects or structures, important for designing, e.g., pipes, turbines, and vessels.
Hydrodynamic device – It is a system which utilizes the kinetic energy, pressure, or flow velocity of liquids (normally water) to perform mechanical work or process fluids. These devices, such as turbines, pumps, or stormwater separators, leverage fluid dynamics principles to manage flow, generate power, or remove pollutants through gravitational, inertial, or viscous forces.
Hydrodynamic entrance length (Lh) – It is the initial pipe or duct length needed for a fluid’s velocity profile to change from a uniform inlet distribution to a stable, fully developed profile (99 % of maximum velocity) because of the viscous boundary layer growth. It is important for determining where pressure drops and convective heat transfer become stable.
Hydrodynamic entrance region – It is the initial length of a pipe or duct where fluid enters, and the velocity profile develops from a uniform shape into a stable, fully developed shape (e.g., parabolic for laminar). It begins at the inlet and ends when boundary layers from the walls merge at the centre-line.
Hydrodynamic entry length (Lh) – It is the initial pipe or duct length needed for a viscous fluid’s velocity profile to transition from uniform to a fully developed (parabolic) profile. It represents the distance where boundary layers merge, with typical approximations being 0.05 X Re x D (laminar) and 10 x D (turbulent).
Hydrodynamic entry length problem – It refers to the analysis of flow development in ducts, where it describes the distance over which the flow transitions from an initial state to a fully developed state, frequently influenced by the geometry of the duct. It involves determining parameters such as pressure drop and velocity profiles in different duct shapes, including equilateral and isosceles triangular ducts.
Hydrodynamic equations – These are mathematical formulations, mainly based on conservation of mass (continuity), momentum (Navier-Stokes), and energy, which describe the motion of fluids and the forces acting upon them. They calculate pressure, velocity, and density changes in liquids and gases to design pipelines, turbines, and marine structures.
Hydrodynamic forces – These are the mechanical pressures and shearing forces exerted by a moving liquid (normally water) on a submerged or partially submerged solid structure. Caused by velocity, density, and viscosity, these forces include positive frontal pressure, downstream suction (negative pressure), and drag / friction, important for designing stable marine structures, bridges, and hydraulic machinery.
Hydrodynamic friction – It is the resistance to motion caused by the viscous shearing of a relatively thick, continuous fluid film which completely separates two moving surfaces. It occurs when surfaces are separated by a lubricant, where friction depends on the fluid’s viscosity, sliding speed, and load, rather than solid contact.
Hydrodynamic interaction – It refers to the fluid-mediated coupling between multiple moving bodies, particles, or surfaces within a flow, where the movement of one body disturbs the surrounding fluid, altering the forces (drag / lift) acting on others. These long-range interactions are important in analyzing collective behaviour in particle suspensions, ship-to-ship wake interference, and emulsion stability.
Hydrodynamic loading – It refers to the time-varying, transient forces exerted by moving fluid (normally water) on submerged or partially submerged structures. These loads, driven by currents, waves, or turbulence, are important in marine, coastal, and offshore engineering, resulting from viscous drag and inertia forces which that cause structural stress, fatigue, or movement.
Hydrodynamic lubrication – It is also known as full film or fluid film lubrication. It is a system of lubrication in which the shape and relative motion of the sliding surfaces causes the formation of a fluid film which has sufficient pressure to separate the surfaces The high lubricant viscosity creates enough fluid pressure to build a supporting film and eliminates all solid-surface contact. The film thickness is quite high in this type of lubrication system compared to others.
Hydrodynamic machining – It is the removal of material by the impingement of a high-velocity fluid against a work-piece.
Hydrodynamic measurements – These measurements involve quantifying fluid motion parameters, mainly velocity fields, pressure distribution, and flow rates, around structures or through systems. These measurements, frequently utilizing tools like ‘particle image velocimetry’ (PIV), are important for optimizing design, analyzing loads, and minimizing drag in applications like pipelines, and offshore structures
Hydrodynamic mass – It is the inertia added to a submerged or partially submerged vibrating / accelerating structure because of the surrounding fluid which is to be moved with it. It acts as an equivalent mass, considerably affecting structural natural frequencies, especially in offshore engineering.
Hydrodynamic model – It is a computational, numerical framework used to simulate and predict the behaviour of water (or fluids) in motion, utilizing governing equations like Navier-Stokes to analyze flow velocity, pressure, and, importantly, depth. These models are necessaryfor mapping floods, designing coastal infrastructure, managing water quality, and predicting ship performance, utilizing inputs such as bathymetry, topography, and tidal forces.
Hydrodynamic performance – It refers to the efficiency, resistance, and stability characteristics of a structure or vessel (like ships, turbines, or subsea pipelines) as it moves through or interacts with water. It measures how effectively a design manages fluid forces, such as drag, lift, and pressure, to optimize motion, energy consumption, and structural stability.
Hydrodynamic pitch angle – It is the angle of a blade’s chord line relative to a plane perpendicular to its axis of rotation, determining the angle of attack and regulating hydrodynamic loads. It is critical for controlling fluid forces, such as maximizing lift in turbines or optimizing propeller efficiency.
Hydrodynamics – It is a sub-discipline of fluid dynamics that studies the motion of liquids. It has a wide range of applications in engineering, including determination of the mass flow rate of petroleum through pipelines, optimization of populsion efficiency, prediction of wave dynamics, and measurement of liquid metal flows. In miniaturization, hydrodynamics becomes increasingly important with the application of hydromechanical system in microforming process and the development of micro fluidics system. Knowledge on hydrodynamic characterization of the fluids helps to optimize the fluids flow and mitigate unwanted effects in the hydromechanical system and micro fluidics system.
Hydrodynamic seal – It is a seal which has special geometric features on one of the mating faces. These features are designed to produce interfacial lift, which arises solely from the relative motion between the stationary and rotating portions of the seal.
Hydrodynamic shear – It is the stress exerted by moving fluid layers on surfaces, particles, or micro-organisms, caused by velocity differences (velocity gradients) within the fluid. It is defined in engineering as the tangential force per unit area responsible for viscous behaviour, particle breakage, and biofilm formation.
Hydrodynamic stability – It is a branch of fluid mechanics analyzing whether a fluid flow remains in its original, orderly state (laminar) or breaks down into chaos (turbulence) when subjected to small perturbations. It determines if applied disturbances to velocity, temperature, or pressure fields die down or grow, leading to flow transition.
Hydrodynamic theory – it is the study of the motion of fluids (liquids and gases) and the forces acting on them, grounded in conservation laws of mass, momentum, and energy. It focuses on fluid-structure interactions, such as drag on ships, pipe flow, and turbine efficiency, often assuming ideal, incompressible flow for initial modeling.
Hydrodynamic trapping – It is a technique using laminar fluid flow within micro-fluidic devices to confine micro-scale/nano-scale particles or cells at a specific, frequently stagnation, point without physical contact or external force fields (optical / electric). It enables high-precision, non-perturbative, long-term observation of particles in free solution.
Hydrodynamic volume – It is the effective, dynamic volume a molecule or particle occupies in a solution, which includes the particle itself and the solvent shell closely associated with it. It represents the volume of a hypothetical hard sphere that diffuses at the same rate as the actual molecule, accounting for its shape, conformation, and solvation.
Hydrodynamic waves – These are time-dependent oscillations and perturbations in a fluid, typically water, influenced by gravity, inertia, boundary conditions (like seabed topography), wind, and currents. They represent the movement of water surface elevations, which are important for calculating loading, wave energy, and structural responses in offshore, coastal, and ocean engineering.
Hydroelasticity – It is the study of the interaction between hydrodynamic, inertial, and elastic forces on deformable structures in water. It analyzes how fluid-induced loads cause structural distortions, which in turn alter the hydrodynamic forces, specifically for marine structures like ships, platforms, and ice.
Hydroelectric energy – It is the renewable generation of electricity by harnessing the gravitational potential and kinetic energy of moving or falling water. Engineering systems, typically dams, turbines, and generators, convert this hydraulic energy into electrical power, frequently achieving 90 % to 95 % efficiency. It serves as a reliable, dispatchable power source.
Hydro-electricity – It is the generation of electric power from the kinetic energy of falling water.
Hydroelectric power generation – It is the process of converting the potential and kinetic energy of flowing or falling water into electrical energy. It utilizes turbines connected to generators, typically harnessed via dams (impoundment) or river diversion, to produce sustainable electricity, frequently achieving 90 % to 95 % efficiency.
Hydroelectric power plant – It is a facility which generates electricity by harnessing the gravitational potential energy of falling or fast-flowing water. It converts this hydraulic energy into mechanical energy using turbines, which then drive generators to produce electrical power, typically providing a renewable, low-carbon, and highly flexible energy source.
Hydro energy – It is a renewable engineering process that converts the potential and kinetic energy of moving or falling water into electrical energy. Using dams, turbines, and generators, engineers harness water flow to drive rotors, converting mechanical energy into electricity. This reliable power source is utilized via reservoirs, run-of-river, or tidal systems
Hydroesterification – It is a two-step, high-yield process used mainly for biodiesel production from low-cost, high-moisture, and high-free fatty acid (FFA) waste oils. It involves the hydrolysis of triglycerides into fatty acids, followed by chemical or enzymatic esterification to convert them into ‘fatty acid methyl esters’ (FAME).
Hydrofining – It is a catalytic process used in oil refining to improve the quality of petroleum products by removing impurities, mainly sulphur, nitrogen, and metals, using hydrogen. It is a form of hydrotreating which operates at high temperatures and pressures to saturate olefins, improve colour, and reduce contaminants, ensuring cleaner-burning fuels.
Hydrofluoric acid – It is a solution of hydrogen fluoride (HF) in water. Solutions of hydrogen fluoride are colourless, acidic and highly corrosive. A common concentration is 49 % (48 % to 52 %) but there are also stronger solutions (e.g., 70 %) and pure hydrogen fluoride has a boiling point near room temperature. It is used to make most fluorine-containing compounds and poly-tetra-fluoro-ethylene material. Elemental fluorine is produced from it. It is commonly used to etch glass and silicon wafers.
Hydrofluoric acid corrosion – It causes severe, aggressive corrosion by destroying protective oxide layers on metals, particularly attacking glass, ceramics, and carbon steel. Common in hydrofluoric acid alkylation units and industrial etching, it causes high-temperature corrosion and wet acid attack. It is a specialized, highly destructive damage mechanism by which hydrofluoric acid reacts with metals, especially carbon steel, causing severe general thinning, localized pitting, and cracking. It is characterized by high, rapid corrosion rates influenced by water content, temperature (above 65 deg C), and acid strength. Alloy 400 (Monel) is frequently used for resistance.
Hydrofluoric acid solution – It refers to a highly acidic solution used in wet etching processes, particularly for glass, where it can react with the glass composition and is often diluted with compounds like ammonium fluoride (NH4F) to stabilize the etching rate.
Hydrofluorocarbons – These are synthetic organic compounds which contain fluorine and hydrogen atoms, and are the most common type of organo-fluorine compounds. Majority are gases at room temperature and pressure.
Hydrofoil – It is a lifting surface or strut which operates in water, generating hydrodynamic lift based on its relative speed and distance below the free surface. Its performance is influenced by factors such as wave drag and pressure conditions near the surface.
Hydroforming – It is a forming process in which a tube is placed into a forming die. The tube is then formed to the shape of the die through the application of internal water pressure. The hydroforming process allows for severe shape deformation, making it ideal for automotive structural parts such as engine cradles, radiator supports, and body rails. Different shaped and sized holes can be punched in the tube almost anywhere during the process.
Hydroform process – In this process, after a hydraulic pump delivers fluid under pressure into the pressure-dome cavity, the punch containing the die is driven upward into the cavity against the resistance provided by the fluid, and the work-piece is formed.
Hydroformylation – It is also called Oxo process. It is an industrial process which converts alkenes into aldehydes by adding a formyl group (-CHO) and a hydrogen atom across a carbon-carbon double bond using synthesis gas (hydrogen and carbon mono-oxide) and a transition metal catalyst (typically cobalt or rhodium). This exothermic, high-pressure reaction produces valuable raw materials for plastics and chemicals.
Hydrogel – It is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. A three-dimensional solid results from the hydrophilic polymer chains being held together by cross-links.] Because of the inherent cross-links, the structural integrity of the hydrogel network does not dissolve from the high concentration of water. Hydrogels are highly absorbent (they can contain over 90 % water) natural or synthetic polymeric networks. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their considerable water content. As responsive ‘smart materials’, hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in majority of the cases by a gel-sol transition to the liquid state. Chemo-mechanical polymers are mostly also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors.
Hydrogel composite – It is a material comprising a 3D, cross-linked polymer network (natural or synthetic) integrated with fillers like nano-particles, fibres, or other polymers to improve properties like mechanical strength, responsiveness, and conductivity. These materials retain high water content while overcoming the low strength of pure hydrogels.
Hydrogen – It is the simplest of all elements. One can visualize a hydrogen atom as a dense central nucleus with a single orbiting electron. In most hydrogen atoms, the nucleus consists of a single proton, although a rare form (or ‘isotope’) of hydrogen contains both a proton and a neutron. This form of hydrogen is called deuterium or heavy hydrogen. Other isotopes of hydrogen also exist, such as tritium with two neutrons and one proton, but these isotopes are unstable and decay radioactively. Hydrogen is the first element in the periodic table with the atomic number 1. It is the lightest and most abundant element in the universe representing 75 % by mass or 90 % by volume of all matter. On earth, it is mostly found in compounds with almost every other element. It also exists as a free element in the atmosphere, but only to the extent of less than 1 parts per million by volume. Free ionic hydrogen is more reactive than molecular hydrogen, the non-polar covalent compound of two hydrogen atoms. Hydrogen can be considered an ideal gas over a wide temperature range and even at high pressures. At standard temperature and pressure conditions, it is a colourless, odourless, tasteless, non-toxic, non-corrosive, non-metallic di-atomic gas, which is in principle physiologically not dangerous. One of its most important characteristics is its low density, which makes it necessary for any practical applications to either compress the hydrogen or liquefy it. It is positively buoyant above a temperature of -251 deg C, i.e., over (almost) the whole temperature range of its gaseous state. The molecules of hydrogen gas are smaller than all other gases, and it can diffuse through many materials considered air-tight or impermeable to other gases. This property makes hydrogen more difficult to contain than other gases. Gaseous hydrogen, with a density of 0.08345 kilogram per cubic metre, has a specific gravity of 0.0696 and is hence around 7 % the density of air. Liquid hydrogen, with a density of 70.78 kilogram per cubic metre, has a specific gravity of 0.0708 and is hence around (and coincidentally) 7 % the density of water.
Hydrogen absorption – It is the process where hydrogen atoms (dissociated from hydrogen gas) penetrate and dissolve into the bulk of a solid material, typically metals or alloys, forming solid solutions or metal hydrides. It is a multi-step phenomenon involving surface physisorption, chemical dissociation, and diffusion into the host lattice.
Hydrogen abstraction – It is a chemical process where a radical species removes a hydrogen atom from a substrate (molecule), resulting in a new radical and a new chemical bond. It is an important reaction in polymerization, combustion, and catalytic hydrocarbon oxidation. It differs from deprotonation since it removes an atom, not a proton.
Hydrogen activity – It is the effective concentration or chemical potential of hydrogen (H+ ions in liquids or H atoms in solids) which actively participates in reactions like corrosion, embrittlement, or catalysis. It represents the ‘available’ or ‘free’ hydrogen, frequently differing from total concentration because of the interatomic forces, and is important for evaluating material damage.
Hydrogen-assisted cracking – It is characterized by the brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. It causes a reduction in the ductility of a metal because of the absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress needed for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen-assisted cracking occurs in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminum, and stainless steels are less susceptible to hydrogen embrittlement.
Hydrogen-assisted stress-corrosion cracking (HSCC) – It is a series of small cracks which present themselves in material after exposure to a corrosive environment containing hydrogen, high temperatures, high tensile or shear stress, or a combination of these factors.
Hydrogenated amorphous silicon (alpha-Si:H) – It is a non-crystalline, disordered semi-conductor alloy containing 4 % to 12 % atomic hydrogen, which passivates silicon dangling bonds to reduce defects. Engineering alpha-Si:H involves using ‘plasma-enhanced chemical vapour deposition’ (PECVD) at 250 deg C to 300 deg C to create low-cost, flexible, large-area thin-film transistors and photo-voltaic devices.
Hydrogenated polyalphaolefins (PAOs) – These are synthetic hydrocarbon fluids, specifically Group IV base oils, produced by the catalytic polymerization and subsequent hydrogenation of alpha olefins. They are known for their excellent thermal and oxidative stability, high viscosity index, and good low-temperature properties. These are a type of synthetic lubricant base oil made by linking together short chains of alpha olefins, which are then hydrogenated (saturated with hydrogen atoms).
Hydrogenation – It is a chemical reaction in which hydrogen atoms are added to an unsaturated compound, converting double or triple carbon–carbon bonds into single (saturated) bonds, typically facilitated by a catalyst. It also refers to the interaction of hydrogen with metals, frequently as an undesirable process leading to embrittlement, or, increasingly, as a clean manufacturing technique, such as using hydrogen to reduce iron ore instead of carbon. It typically involves hydrogen dissolution or chemical interaction with the metal. It is a process which saturates the double bonds in the alpha olefin molecules, resulting in a more stable and thermally robust molecule.
Hydrogenation process – It is an exothermic industrial process which adds molecular hydrogen (H2) to unsaturated organic compounds (alkenes, alkynes, oils) to form saturated compounds (alkanes, fats). Engineered as a catalytic reaction using metals like Nickel, Palladium, or Platinum, it breaks double / triple bonds, frequently improving product stability and texture.
Hydrogen based steelmaking route – It has been studied in ULCOS (ultra-low CO2 steelmaking) project, Hydrogen is considered to be produced by water electrolysis using hydraulic or nuclear electricity. Iron ore is considered to be reduced to direct reduced iron by hydrogen in a shaft furnace, and carbon-free direct reduced iron is considered to be treated in an electric arc furnace to produce steel. This route shows promising performance regarding carbon di-oxide emissions which is less than 300 kilograms of carbon di-oxide per ton of steel, including the carbon di-oxide-cost of electricity with the emissions from the direct reduction furnace itself being almost zero. This represents 85 % cut in carbon di-oxide emissions as compared to the present around 1,850 kilograms of carbon di-oxide per ton of steel of the blasé furnace-basic oxygen furnace route. This new route hence is a more sustainable way for making steel. However, its future development is largely dependent on the emergence of a so-called hydrogen economy, when this gas becomes available in large quantities, at competitive cost, and with low carbon di-oxide emissions for its production.
Hydrogen behaviour – It refers to the study and analysis of how hydrogen gas and atoms act, move, and interact with materials, particularly metals, under different environmental conditions (temperature, pressure, chemical environment) and mechanical stresses. This field is important for the safe design and operation of energy infrastructure, such as pipelines, storage tanks, and fuel cells, where hydrogen can cause degradation of material integrity.
Hydrogen blistering – It consists of the formation of blisters on or below a metal surface from excessive internal hydrogen pressure. Hydrogen may be formed during cleaning, plating, or corrosion.
Hydrogen bond length – It is the distance between the donor atom (X) and the acceptor atom (Y) in an X – H — Y system, normally measuring between 160 pico-meters to 200 pico-meters (1.6 angstrom to 2 angstrom). This distance is shorter than the sum of the van der Waals radii of the ‘H’ and ‘Y’ atoms, indicating a partly covalent, electrostatic interaction which considerably affects material properties.
Hydrogen brazing – It is a term which is sometimes used to denote brazing in a hydrogen-containing atmosphere, normally in a furnace. Use of the appropriate process name is preferred.
Hydrogen bubbles – These are gas-filled pockets, typically hydrogen (H2), generated through water electrolysis at a cathode. They are used for flow visualization because of their ability to trace streamlines, but they also represent a critical failure mechanism (hydrogen blistering /embrittlement) where accumulated atomic hydrogen creates pressure voids, weakening metal structures.
Hydrogen burning – It refers to the exothermic chemical oxidation of hydrogen (H2) with oxygen (O2) to generate heat, mainly producing water vapour (H2O) and minimal nitrogen oxides (NOx). It is a high-speed, wide-flammability range combustion process used in modified turbines and engines for power generation or propulsion, frequently aimed at reducing carbon di-oxide (CO2) emissions.
Hydrogen capture – It involves the technological processes of extracting, separating, and isolating pure hydrogen (H2) from compounds (like methane or water) or industrial waste streams. It focuses on maximizing purity and efficiency, frequently integrating with carbon capture for low-carbon (blue) hydrogen production through steam-methane reforming.
Hydrogen-carbon (H/C) ratio – It refers to the ratio of hydrogen to carbon atoms in a substance, which is a key characteristic of heavy oil and bitumen, indicating the extent of upgrading processes which improve the ratio through thermal cracking and hydrogenation. An increase in the hydrogen /carbon ratio is associated with the production of lighter components and reduced viscosity in heavy feedstock.
Hydrogen charge – It refers to the process of introducing hydrogen into a material, typically through electro-chemical methods or gaseous hydrogen charging, to analyze its content and behaviour within the material using techniques such as thermal desorption analysis (TDA).
Hydrogen charged sample – It is a material sample subjected to electro-chemical or gaseous hydrogen charging to introduce hydrogen into its micro-structure. It is used to study hydrogen embrittlement, fatigue behaviour, and mechanical property changes, such as reduced ductility or increased strength, resulting from hydrogen diffusion, frequently analyzed using thermal desorption spectroscopy.
Hydrogen charging – It is a process which introduces hydrogen into materials, typically metals or alloys, using electro-chemical (cathodic) or gaseous methods to study its effects, such as embrittlement, degradation, or diffusion, frequently analyzed through thermal desorption spectroscopy. It is used to simulate industrial failures, like hydrogen flaking, by assessing a material’s sensitivity to hydrogen concentration under controlled conditions.
Hydrogen complex – It typically refers to a localized microscopic structure formed when hydrogen atoms interact with, bond to, or become trapped by defect sites (impurities, vacancies) within a host material’s crystal lattice. These complexes, such as donor-hydrogen or acceptor-hydrogen pairings in semi-conductors, considerably alter the electronic and physical properties of the material.
Hydrogen compression – It is the process of reducing the volume of hydrogen gas to increase its pressure, enabling efficient storage (typically 20 mega-pascals to 95 mega-pascals) and transportation. Since hydrogen has low density and high energy potential, specialized compressors (reciprocating, diaphragm, or ionic) are needed to increase its volumetric density for applications like fuel cell vehicles and industrial use.
Hydrogen corrosion – It is the degradation of metals, (mainly steels) caused by atomic hydrogen absorption, leading to embrittlement, cracking, or loss of ductility. It frequently occurs via cathodic hydrogen evolution in acidic, high-temperature, or high-pressure environments, where atomic hydrogen enters the metal lattice, causing internal stresses, blisters, or premature failure under tensile load.
Hydrogen cracks – Hydrogen cracking results from the presence of hydrogen medium and normally occurs in conjunction with the presence of applied tensile stress or residual stress. Hydrogen can be already present in the metal due to previous processes such as electroplating, pickling, and welding in moist atmosphere or the melting process itself. Also, hydrogen can come from the presence of hydrogen sulphides, water, methane or ammonia in the work environment of a material. Hydrogen can diffuse in the metal and initiate very small cracks at subsurface cites (normally at the grain boundaries) subjected to high values of stress. The presence of such cracks at several locations causes ductile materials to show brittle fracture behaviour.
Hydrogen damage – It is the degradation of metallic materials, mainly steel, caused by the diffusion of atomic hydrogen into the lattice, leading to loss of ductility, cracking, or failure. It occurs through environmental exposure, corrosion, or processing, manifesting as embrittlement, blistering, internal cracking under stress, and hydride formation. These can occur when hydrogen is present in some metals.
Hydrogen desorption – It is the process by which hydrogen atoms or molecules are released from a substrate, typically a solid adsorbent or metal hydride, back into the surrounding gas phase or vacuum. It is the reverse of the hydrogen adsorption / absorption process. This process is important in hydrogen energy storage, metallurgy (preventing hydrogen embrittlement), and catalysis, as it involves overcoming the bonding or trapping energy holding the hydrogen within or on the material.
Hydrogen desorption temperature – It is the specific temperature at which a stored hydrogen material (e.g., metal hydride) releases hydrogen by overcoming its binding energy, typically identified as the peak temperature in ‘thermal desorption spectroscopy’ (TDS). It is an important metric for hydrogen storage efficiency, dictated by the enthalpy of desorption.
Hydrogen diffusion – It refers to the process by which atomic hydrogen moves through the crystal lattice of a metal or alloy, typically from regions of high concentration to low concentration. Because of the small size of hydrogen atoms, they are highly mobile, allowing them to penetrate solid metals more easily than other elements.
Hydrogen dilution – it is a process which involves reducing the concentration of hydrogen in a mixture by adding a non-reactive gas (like nitrogen or argon) or using it as a carrier gas in chemical vapour deposition. It is used to control reaction rates, improve film quality, improve material structure, or improve safety by lowering flammability.
Hydrogen distribution – It refers to the infrastructure and processes used to transport hydrogen from production plants or storage facilities to end-users (fueling stations, industrial consumers). It involves managing complex networks, high-pressure pipelines, tube trailers, or liquid tankers, to handle varying pressures, purities, and flow rates while addressing safety challenges like leakage and material embrittlement.
Hydrogen di-sulphide (H2S2) – It is a pale yellow, volatile inorganic compound and chemical intermediate which readily decomposes into hydrogen sulphide (H2S) and sulphur. It is frequently associated with the breakdown of poly-sulphides or as a specialized chemical species, distinct from the common industrial pollutant, hydrogen sulphide (H2S).
Hydrogen efficiency – It measures the ratio of useful hydrogen energy output to total energy input (electricity or thermal) during production, storage, or conversion. It indicates how effectively energy is converted into chemical energy, with typical electrolysis efficiency at 70 % to 80 % and fuel cell efficiency between 40 % to 60 %.
Hydrogen electrode – It is an electro-chemical reference electrode that allows for variations in proton activity within the electrolyte, with the ‘reversible hydrogen electrode’ (RHE) being a practical form which is sensitive to pH changes. It is used in studies of catalyst activity and in applications like low temperature fuel cells and electrolyzers.
Hydrogen embrittlement – It is a process resulting in a decrease of the toughness or ductility of a metal because of the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes super-saturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during high-temperature thermal treatments and in service during electro-plating, contact with maintenance chemicals, corrosion reactions, cathodic protection, and operating in high-pressure hydrogen. In the absence of residual stress or external loading, environmental hydrogen embrittlement is manifested in various forms, such as blistering, internal cracking, hydride formation, and reduced ductility. With a tensile stress or stress-intensity factor exceeding a specific threshold, the atomic hydrogen interacts with the metal to induce sub-critical crack growth leading to fracture. In the absence of a corrosion reaction (polarized cathodically), the normal term used is hydrogen-assisted cracking (HAC) or hydrogen stress cracking (HSC). In the presence of active corrosion, normally as pits or crevices (polarized anodically), the cracking is normally called stress corrosion cracking (SCC), but it is more properly be called hydrogen assisted stress-corrosion cracking (HSCC). Hence, hydrogen stress cracking and electro-chemically anodic stress corrosion cracking can operate separately or in combination (hydrogen assisted stress-corrosion cracking). In some metals, such as high-strength steels, the mechanism is believed to be all, or nearly all, hydrogen stress cracking. The participating mechanism of hydrogen stress cracking is not always recognized and can be evaluated under the generic heading of stress corrosion cracking.
Hydrogen emission – It refers to the release of molecular hydrogen (H2) into the atmosphere, frequently occurring during production, transport, or storage, and acts as an indirect greenhouse gas. It also refers to the light spectrum emitted by excited hydrogen atoms in spectroscopic analysis.
Hydrogen energy – It is a versatile, clean energy carrier produced by extracting hydrogen from compounds like water or natural gas, mainly for use in fuel cells or combustion to generate electricity and heat. Engineered systems focus on low-carbon production (electrolysis, reforming), high-density storage, and efficient transportation to enable decarbonization.
Hydrogen energy storage – It is the process of converting excess electricity (frequently from renewable sources) into hydrogen gas through electrolysis, storing it under high pressure, liquification, or in solid-state materials, and converting it back into electricity or fuel for industrial, transportation, or grid applications. This system acts as a long-duration energy buffer.
Hydrogen energy system – It is an integrated infrastructure designed to produce, store, transport, and convert hydrogen as a clean, secondary energy carrier (vector). It links renewable or main energy sources to end-uses like electricity generation, transportation (fuel cells), and industrial heating, with water and heat as main by-products.
Hydrogen engine – It is a modified internal combustion engine (reciprocating Otto cycle) which burns hydrogen gas, or sometimes liquid hydrogen, instead of conventional fossil fuels. It acts as a zero-carbon power source by injecting hydrogen into the combustion chamber to produce mechanical work and water vapour, with minimal nitrogen oxides (NOx).
Hydrogen evolution reaction – It is a fundamental electro-chemical process occurring at the cathode during water electrolysis, where protons (H+) or water molecules (H2O) are reduced by electrons (e-) to produce hydrogen gas (H2). It is an important, multi-step reaction necessary for green hydrogen production.
Hydrogen explosion – It is a rapid, highly energetic oxidation reaction occurring when hydrogen gas (H2) mixes with oxygen (O2), typically 4 % to 75 % concentration in air, and is ignited. As an important industrial hazard, it releases substantial energy through deflagration (subsonic) or detonation (supersonic) waves, frequently causing severe damage because of high-pressure shock-waves.
Hydrogen fire – It is a hazard defined as the combustion of hydrogen gas (H2) with an oxidizer, typically air, characterized by a nearly invisible flame, low radiant heat, and a wide flammability range (4 % to 75 % in air). It produces mainly water and heat, making detection difficult without specialized ultra-violet / infra-red (UV / IR) sensors.
Hydrogen flakes – Hydrogen is available during the different process operations (from decomposition of water vapour, hydrocarbons, or atmosphere etc.) and it dissolves in material at temperatures above 200 deg C. Hydrogen flakes are thin subsurface discontinuities which develop during cooling of large size sections produced by rolling or forging because of the entrapment of hydrogen resulting from rapid cooling.
Hydrogen fluoride (HF) – It is a colourless, highly corrosive, and volatile inorganic compound used as a critical reagent for refining, surface treatment, and processing, particularly for aluminum, steel, and uranium. It serves as a main source for creating fluorine compounds, and its aqueous solution is known as hydrofluoric acid.
Hydrogen fluoride cleaning – It refers to the use of hydrogen fluoride gas or aqueous hydrofluoric acid to remove stubborn contaminants, specifically, silicon-based oxides, scales, and rust, from metal surfaces. It is a highly aggressive, specialized surface treatment frequently used on high-performance materials like titanium, stainless steel, and nickel-based superalloys.
Hydrogen flux – It defines the rate at which hydrogen atoms move, penetrate, or diffuse through a material (normally metal) per unit area and time, typically expressed in units like mol per square centimeter second or kilograms per square centimeter second. It indicates the intensity of hydrogen permeation, frequently driven by concentration gradients in corrosion processes or high-temperature, high-pressure environments, acting as an important indicator for hydrogen embrittlement risk.
Hydrogen fuel – Hydrogen is able to react chemically with most other elements. In connection with oxygen, hydrogen is highly flammable over a wide range of concentrations. As a fuel, it represents a clean, environmentally friendly energy source. The mass-related energy density of hydrogen is very high. 1 kilogram of hydrogen contains 132.5 MJ (mega joule), which is around 2.5 times more energy than is contained in 1 kilogram of natural gas. The energy content of hydrogen is given either as lower heating value (LHV) of 242 kJ/mol or as higher heating value (HHV) of 286 kJ/mol. The difference is 15.4 %, which is large compared to other gases. It is because of the heat liberated upon condensation of the water vapour (which can be captured in a turbine, but not in a fuel cell). A stoichiometric hydrogen-air mixture, where all fuel is consumed upon reaction, i.e., where maximum combustion energy is released, contains 29.5 % by volume of hydrogen. The combustion product of hydrogen is water vapour. It burns in a non-luminous, almost invisible pale blue, hot flame to water vapour liberating the chemically bound energy as heat (gross heat of combustion). The flame temperature of a burning (pre-mixed stoichiometric) hydrogen-air mixture is 2,130 deg C maximum. There is a wide flammability range of hydrogen (at room temperature) between 4 % and 75 % by volume of concentration in air and up to 95 % by volume in oxygen. The lower flammability limit (LFL) as the minimum amount of fuel which supports combustion, is normally the ‘more important’ limit, since it is reached first in a continuous leakage. The flammability range widens with higher temperatures.
Hydrogen fuel cell – It is an electro-chemical energy conversion device which directly converts the chemical energy of hydrogen (H2) and oxygen (O2) into electricity, heat, and water. Operating continuously when fuel is supplied, it consists of an anode, cathode, and electrolyte, typically producing zero carbon di-oxide (CO2) emissions.
Hydrogen fuel cell system – It is an electro-chemical power generation unit which directly converts chemical energy from hydrogen (H2) and oxygen (O2) into electricity, with heat and water vapour as the only byproducts. Engineered as a sustainable, high-efficiency energy source, it typically consists of a fuel cell stack, fuel storage / supply, and thermal management / water management components, frequently operating at around 60 % efficiency for stationary or transportation applications.
Hydrogen fuel cell technology – It is an electro-chemical energy conversion device which directly transforms the chemical energy of hydrogen (H2) and oxygen (O2) into electricity, producing only water (H2O) and heat as by-products. Engineered for high efficiency without combustion, it enables clean power generation for transportation and industrial applications.
Hydrogen fuel cell vehicle – It is an electric vehicle which generates its own electricity onboard using a fuel cell stack, combining hydrogen gas with oxygen to power electric motors. Unlike battery electric vehicles, they refuel in 3 minutes to 5 minutes, emit only water vapour, and use high-pressure storage tanks, offering long-range, zero-emission transportation.
Hydrogen-fueled vehicles – These are motor vehicles which utilize hydrogen as a fuel source, frequently using fuel cells to power electric motors, or using hydrogen directly for combustion. These vehicles are noted for their potential higher efficiencies and the ability to be produced domestically, though their adoption is limited by the availability and cost of hydrogen fueling infrastructure.
Hydrogen furnace atmosphere – It is a controlled, highly reducing environment containing pure hydrogen (H2) or hydrogen mixed with inert gases (like Nitrogen, N2) or other gases (like ammonia, NH3), used in thermal processing to prevent oxidation, reduce existing metal oxides, and clean metal surfaces at high temperatures. It is normally used for bright annealing, sintering, and brazing of materials like stainless steel, copper, and specialty alloys, frequently leaving the work-piece with a clean, unoxidized surface.
Hydrogen gas (H2) – It is a colourless, odourless, tasteless, and highly flammable diatomic gas, utilized as a high-efficiency, clean energy carrier and industrial feedstock. It is characterized by its extremely low density, high diffusion capacity, and potential to produce only water vapour during combustion, making it important for fuel cells, chemical processing, and metallurgical applications.
Hydrogen generation – It is also called hydrogen production. It is the engineered process of extracting hydrogen (H2) from hydrogen-containing compounds, such as water, natural gas, biomass, or coal, using chemical, electrical, or thermal techniques. It is necessary for creating clean energy carriers for fuel cells, transportation, and industrial applications.
Hydrogen generator – It is a system which produces hydrogen gas on-site, typically through electrolysis, by using electricity to split water (H2O) into hydrogen and oxygen. Mainly utilizing proton exchange membranes (PEM) or alkaline technology, these systems provide a safe, continuous, and high-purity supply for industrial or laboratory applications, eliminating the need for bottled gas.
Hydrogen hazards – These are the specific physical, chemical, and mechanical risks associated with using hydrogen, mainly stemming from its extreme flammability (4 % to 75 % in air), low ignition energy, small molecular size leading to leaks, and material degradation like hydrogen embrittlement. These risks necessitate specialized safety design, including ventilation, leak detection, and material selection.
Hydrogen-induced cracking – It is the cracking in low-to medium-strength steels in the absence of applied stress where the driving force for crack propagation is molecular hydrogen pressure build-up within the crack.
Hydrogen-induced delayed cracking – It is a term sometimes used to identify a form of hydrogen embrittlement in which a metal appears to fracture spontaneously under a steady stress less than the yield stress. There is normally a delay between the application of stress (or exposure of the stressed metal to hydrogen) and the onset of cracking.
Hydrogen-induced stress cracking – It is also called hydrogen stress cracking .it is a form of hydrogen embrittlement where high-strength alloys fracture under tensile stress and environmental hydrogen exposure. It occurs when atomic hydrogen diffuses into the metal, reducing ductility and causing brittle failure, frequently below the yield strength, typically seen in pipelines and fasteners.
Hydrogen infrastructure – It is the comprehensive network of facilities and systems needed for the production, storage, transportation, and dispensing of hydrogen fuel, forming a complete supply chain from source to end-user. It includes production plants (electrolysis / reforming), pipelines, tube trailers, liquefication plants, and refueling stations.
Hydrogen ion concentration – It is the molar amount of hydrogen ions (H+) present in a solution, normally expressed in moles per litre or ‘M’, which determines its acidity or alkalinity. It is frequently represented by pH, calculated as the negative logarithm of the hydrogen ion concentration ‘pH = -log (H+)’.
Hydrogen isotopes – These are atomic variants of hydrogen containing one proton but differing neutron counts, resulting in distinct atomic masses namely protium (1H, 0 neutrons), deuterium (2H or D, 1 neutron), and tritium (3H or T, 2 neutrons). Applications focus on using deuterium and tritium as nuclear fusion fuels, tracers, because of their unique mass-based physical properties.
Hydrogen levels – These normally refer to the quantity of diffusible hydrogen present in deposited weld metal, important for preventing hydrogen-induced cracking (HIC) or cold cracking in steel. It is measured in milli-litre per 100 grams of deposited metal using methods like mercury or glycerin extraction.
Hydrogen liquefaction – It is an energy-intensive industrial engineering process which converts hydrogen gas into a liquid state (LH2) by cooling it to cryogenic temperatures below -250 deg C (20 K) at atmospheric pressure. It considerably increases storage density, necessary for transportation, utilizing compression, precooling, and expansion cycles (e.g., Claude cycle).
Hydrogen loading – It refers to the process of introducing hydrogen atoms into a material (normally metals) or onto a surface, frequently through high-pressure gas exposure or electrolysis. It is used for surface modification, studying material properties, or storing hydrogen in hydrides, but it can also cause structural damage like embrittlement.
Hydrogen loss – It is the loss in weight of metal powder or a compact caused by heating a representative sample as per a specified procedure in a purified hydrogen atmosphere. Broadly, it is a measure of the oxygen content of the sample when applied to materials containing only such oxides as are reducible with hydrogen and no hydride-forming element.
Hydrogen molecule (H2) – It is the simplest diatomic molecule, consisting of two hydrogen atoms held together by a single covalent bond (sigma bond). As the smallest molecule in nature, it is a colourless, odourless, highly flammable gas normally known as di-hydrogen. Each molecule contains two protons and two electrons.
Hydrogenolysis – It is a catalytic, reductive decomposition process where hydrogen (H2) breaks, or cleaves, chemical bonds (mainly C-C, C-O, C-N, or C-S) in organic molecules. Frequently used in biomass conversion, petroleum processing, and polymer recycling, this method breaks large, complex, or low-value molecules into smaller fragments or monomers. It is typically catalyzed by metal particles in acidic or basic media. It is a key process in the conversion of biomass-derived substrates into valuable industrial chemicals by facilitating partial or complete deoxygenation.
Hydrogen over-voltage – In electro-plating, it is the over-voltage associated with the liberation of hydrogen gas.
Hydrogen oxidation reaction – It is an electro-chemical process where molecular hydrogen (H2) is oxidized on a catalyst surface (typically platinum), losing electrons to form hydrogen ions (H+) or water. It is an important anode reaction in fuel cells, generating electricity by breaking H2 into protons and electron (H2 = 2H+ + 2e-).
Hydrogen-oxygen reaction – It is a highly exothermic combustion process where hydrogen (H2) and oxygen (O2) gases react to form water (H2O) and release substantial heat / light. Represented by the equation 2H2(g) + O2(g) = H2O (l), this combination reaction needs an initiation source (e.g., a spark) and is frequently explosive.
Hydrogen partial pressure, P(H2) – It is the, pressure which hydrogen gas exerts if it alone occupied the entire volume of a mixture at the same temperature. It represents the concentration of hydrogen in a gaseous mixture, determined by multiplying the total pressure by the hydrogen mole fraction.
Hydrogen permeability – It is the measure of how easily hydrogen gas (or atoms) can pass through a material, defined as the product of the hydrogen solubility (how much dissolves) and diffusivity (how fast it moves). It represents the rate of hydrogen transport, often calculated using Fick’s laws and Sieverts’ law for metals.
Hydrogen permeating flux – It refers to the rate at which hydrogen atoms diffuse through a metal from one side to the other, driven by a concentration gradient, and is quantitatively measured by the oxidative current density during electrochemical tests.
Hydrogen permeation flux – It is the rate at which hydrogen atoms (or molecules) pass through a unit area of a material (typically metal) per unit time, driven by a concentration or pressure gradient. It is defined as the volume or molar rate of hydrogen transport, frequently quantified by oxidative current density in electro-chemical tests.
Hydrogen per-oxide – Its chemical formula is H2O2. It is a powerful, eco-friendly oxidizing agent and etchant, normally used in aqueous solutions. It is important for surface treatment, cleaning, and chemical milling of metals. particularly in printed circuit board (PCB) production, because of its ability to dissolve contaminants and etch copper, yielding water and oxygen as byproducts.
Hydrogen pickup – It refers to the process by which atomic hydrogen, generated by environmental interactions (such as corrosion or chemical processing), is absorbed into the bulk of a metal or alloy. This phenomenon is important since the ingested hydrogen can diffuse through the metal lattice, causing embrittlement, cracking, and premature structural failure.
Hydro-pneumatic die cushion – It is an advanced blank-holding system for metal-forming presses which combines the high force capabilities of hydraulic systems with the compressibility (cushioning) of pneumatic systems. It is used to provide precise, adjustable blank-holder force (BHF) during deep drawing, reducing defects like tearing or wrinkling. Unlike simple pneumatic systems, these use oil to transfer force and gas (nitrogen) to act as a spring, reducing high impact surge pressures (shock loads) during the press slide stroke.
Hydrogen probe – It is a specialized sensor designed to detect and measure hydrogen concentration, mainly used in industrial settings for monitoring corrosion, hydrogen embrittlement, or for measuring hydrogen levels in molten steel. It works by detecting atomic hydrogen which diffuses through steel or, in molten metal, by using a carrier gas to analyze the melt.
Hydrogen production – It is the process of extracting and isolating hydrogen molecules (H2) from hydrogen-containing compounds, such as water, natural gas, or biomass, using chemical, electrical, or thermal energy. It involves methods like steam methane reforming (SMR), electrolysis, or gasification to achieve specific purity levels for industrial applications.
Hydrogen production cost – It is the total financial expenditure required to produce hydrogen, calculated as the sum of annualized capital expenses (CAPEX) and operating expenses (OPEX), normally expressed per kilogram. It covers infrastructure, energy, feedstock, labour, and maintenance, heavily influenced by production technology (e.g., electrolysis, steam reforming).
Hydrogen production for fuel cells – It is the process of extracting and isolating high-purity hydrogen (H2) from different sources, mainly natural gas, water, or biomass, using methods like steam reforming, electrolysis, or thermochemical processes. This produced hydrogen acts as a clean energy carrier, fueling fuel cells to generate electricity, water, and heat.
Hydrogen production process – It refers to different industrial or technological processes of extracting and isolating hydrogen gas (H2) from hydrogen-containing compounds, such as water, hydrocarbons (natural gas, coal), or biomass, using thermal, electro-chemical, or biological methods to serve as an energy carrier. There are nine main processes identified, including steam reformation, electrolysis, and bacterial fermentation.
Hydrogen-reduced powder – It is the powder produced by the hydrogen reduction of a metal oxide.
Hydrogen reduction – It is a process which occurs at 800 deg C to 1,000 deg C, where solid regolith is reacted with hydrogen to produce water, which is then to be separated, purified, and electrolyzed to yield hydrogen and oxygen for storage and reuse. The process mainly reduces the iron oxide fraction of regolith, resulting in a yield that depends on its iron content.
Hydrogen reduction process – It is a process which uses hydrogen gas (H2) to remove oxygen from metal oxides at high temperatures (typically 800 deg C to 1,000 deg C). It converts ore into pure metals or metal powders, producing water vapour (H2O) as the only byproduct. It is a key sustainable method for producing direct reduced iron (DRI) without carbon di-oxide emissions.
Hydrogen safety – It encompasses the practices, engineering controls, and standards used to safely produce, handle, store, and utilize hydrogen, addressing its unique risks like high flammability, wide ignition range, and metal embrittlement. It focuses on preventing leaks, ensuring proper ventilation, and managing ignition sources to protect people and property.
Hydrogen-selective membranes – These refer to membranes designed for hydrogen purification, which can be classified into polymeric, inorganic, and metal-organic framework (MOF) types. These membranes utilize materials such as polyimides, ceramics, palladium, zeolites, and graphene to facilitate selective gas permeability and separation of hydrogen from other gases.
Hydrogen selenide – It is a chemical compound with the formula H2Se, characterized as a toxic and flammable gas which can form explosive mixtures with air. It is mainly known for its applications as a dopant in semiconductors and poses health risks such as irritation to the eyes, skin, and respiratory system.
Hydrogen separation membrane – It is a selectively permeable material designed to isolate high-purity hydrogen from gas mixtures (like syngas or natural gas) by allowing only hydrogen to pass through while blocking other gases. These membranes operate based on solution-diffusion or molecular sieving, utilizing dense metals (e.g., palladium), ceramics, or polymers to improve efficiency in purification.
Hydrogen solubility – It is the maximum concentration of hydrogen which can dissolve into a liquid or solid metal lattice while in thermodynamic equilibrium with the surrounding atmosphere at a specific temperature and partial pressure. This concentration, frequently governed by Sieverts’ law, increases with temperature and is proportional to the square root of the hydrogen partial pressure.
Hydrogen source – It is a material or energy process used to produce hydrogen gas (H2), which is a clean, non-toxic energy carrier which is to be extracted from other substances like water (H2O) or fossil fuels. Common sources include natural gas (through steam reforming), biomass, and renewable electricity (through electrolysis).
Hydrogen storage – It is the technology used to contain hydrogen in gaseous, liquid, or solid forms for future energy applications. It acts as an important enabler for fuel cells, transportation, and stationary power by managing hydrogen’s low density and high energy-per-mass ratio. Common methods include high-pressure tanks (compressed gas), cryogenic tanks (liquid), and solid-state materials.
Hydrogen storage for fuel cells – It is the critical technology of containing hydrogen, typically as a high-pressure gas, cryogenic liquid, or within solid materials, to enable its use as an energy carrier for electricity generation in mobile or stationary applications. It overcomes hydrogen’s low density to provide compact, high-mass-energy storage, which is necssary for fuel cell systems.
Hydrogen stress cracking – It is characterized by the brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. It is a form of cracking occurring when corrosion from certain acids causes atomic hydrogen to penetrate higher strength steels.
Hydrogen sulphide (H2S) – It is a colourless, highly toxic, flammable, and corrosive gas with a distinct ‘rotten egg’ odour. It is frequently referred to as sour gas, sewer gas, or swamp gas. Iit is recognized as a hazardous byproduct of anaerobic bacterial decomposition of organic matter, common in wastewater treatment, oil and gas extraction, mining, and chemical manufacturing.
Hydrogen sulphide corrosion – It is also called sour corrosion. It is the deterioration of metals (mainly steel) caused by exposure to hydrogen sulphide (H2S) in the presence of water. It is a destructive electro-chemical process forming black iron sulphide scale, leading to severe pitting, pipeline failures, and hydrogen-induced cracking (HIC) or sulphide stress cracking (SSC)
Hydrogen sulphide stress cracking – It is a form of hydrogen embrittlement occurring when high-strength steels or alloys undergo brittle failure because of the combined action of tensile stress, localized corrosion, and atomic hydrogen penetration in wet hydrogen sulphide (H2S) environments. It is mainly caused by hydrogen atoms diffusing into the metal matrix, reducing ductility and causing cracking at relatively low temperatures (near ambient).
Hydrogen technologies – These refer to the several methods and processes used for the production, conversion, storage, and utilization of hydrogen as an energy vector. These technologies encompass electrocatalytic and catalytic methods, including hydrogen production from renewable sources and diverse applications in industries such as ammonia synthesis and fuel cells.
Hydrogen termination – It is the chemical process of saturating dangling bonds on a solid surface (normally silicon or diamond) with hydrogen atoms to create a stable, hydrophobic, and electronically passivated layer. It is mainly used to prevent oxidation, remove impurities, and control surface conductivity in semi-conductor manufacturing and nano-technology, frequently achieved through hydrofluoric acid etching.
Hydrogen transfer – It is a chemical process involving the migration of hydrogen atoms, protons (H+), or hydride ions (H-) from a donor molecule to an acceptor molecule, normally facilitated by a catalyst. It is a key mechanism in reduction reactions, specifically transfer hydrogenation, used to saturate compounds without using hydrogen gas, relying instead on sources like alcohols or formic acid.
Hydrogen transportation – It refers to the methods, technologies, and infrastructure used to move hydrogen from its production site to end-users (such as fuel stations or industrial plants). Since hydrogen has low volumetric energy density, it is transported in compressed, liquid, or chemical carrier forms through pipelines, trucks, or ships.
Hydrogen traps – These are microscopic lattice defects, boundaries, or precipitates (e.g., carbides, dislocations, grain boundaries) which capture and immobilize hydrogen atoms within a metal’s structure, preventing their movement. These sites are categorized as either reversible traps (lower binding energy, e.g., dislocations) or irreversible traps (higher binding energy, e.g., stable precipitates). Hydrogen traps manage hydrogen mobility to mitigate hydrogen embrittlement by trapping diffusible hydrogen, reducing the amount available to move to high-stress areas.
Hydrogen underground storage – It is the large-scale, long-term storage of compressed hydrogen gas within geological formations, specifically salt caverns, depleted oil / gas reservoirs, and deep aquifers, to balance intermittent supply with fluctuating demand. It serves as a cost-effective, high-capacity solution for seasonal energy storage, important for net-zero energy grids.
Hydrogen utilization – It refers to the technologies, methods, and applications which consume hydrogen as a fuel, energy carrier, or chemical feedstock to generate power, heat, or materials. It is an important component of decarbonization strategies across industries, including refining, transportation, and power generation, aimed at reducing greenhouse gases by producing only water as a by-product when combusted or used in fuel cells.
Hydrological cycle (water cycle) – It is the process by which water evaporates from oceans and other bodies of water, accumulates as water vapour in clouds, and returns to oceans and other bodies of water as rain and snow or as runoff from this precipitation or groundwater.
Hydrogeological modeling – It is the process of creating a simplified, three-dimensional mathematical representation of a groundwater system (aquifer) to simulate, analyze, and predict the behaviour of sub-surface water flow and contaminant transport. It uses computational tools to aid in water resource management, remediation strategies, and impact assessment.
Hydrogeology – It is the part of hydrology which deals with the distribution and movement of groundwater in the soil and rocks of the earth’s crust, most commonly in aquifers.
Hydro-isomerization – It is a catalytic industrial process which converts linear (normal) paraffins / alkanes into branched isomers in the presence of hydrogen. It is used in oil refining to improve fuel quality by increasing the octane number of gasoline or improving the cold-flow properties (lowering the pour point) of diesel and lubricants.
Hydro-isomerization reactions – These reactions refer to processes which improve the composition and properties of hydrocarbons by inducing alkyl branching, which is necessary for reducing pour point and maintaining viscosity. These reactions typically occur in fixed-bed reactors using noble metal catalysts at high temperatures and pressures.
Hydrokinetic energy – It is a renewable form of energy harnessed from the natural motion of water, specifically ocean waves, tides, and river currents, without needing large dams or reservoirs. It converts the movement of water into electricity using specialized turbines submerged directly into the flow.
Hydrokinetic power – It is a form of renewable energy derived from the natural movement (kinetic energy) of water in rivers, tidal currents, and ocean waves, converted into electricity using turbines without the need for large dams or water impoundment. It utilizes water velocity, not gravity head, to drive generators.
Hydrokinetics – It is the study or utilization of the motion of fluids (liquids and gases), focusing on dynamic, flowing situations rather than static, resting ones. In energy contexts, it specifically refers to harnessing the kinetic energy from moving water, such as ocean currents, tides, and rivers, using turbines to generate electricity without needing dams.
Hydrokinetic turbine – It is a renewable energy device which converts the kinetic energy of naturally flowing water, such as rivers, tidal streams, or canals, directly into electricity without needing dams, barrages, or large reservoirs. Similar to wind turbines, they utilize rotor blades placed directly in the current to harness energy.
Hydrological variability – It refers to the natural, temporal, and spatial fluctuations in water quantity, distribution, and timing, including precipitation, streamflow, and groundwater levels. It spans short-term (hourly / daily) to long-term (seasonal / annual) variations, considerably impacting water availability, ecosystem dynamics, and infrastructure design.
Hydrology – It is the science dealing with the properties, distribution, and flow of water on or in the earth.
Hydrolysis – It consists of decomposition or alteration of a chemical substance by water. In aqueous solutions of electrolytes, it is the reactions of cations with water to produce a weak base or of anions to produce a weak acid.
Hydrolysis process – It is a process which breaks down complex molecules into simpler ones by adding water (H2O) to break chemical bonds. The process typically splits the substrate into two parts, with one part gaining a hydrogen ion (H+) and the other gaining a hydroxyl group (OH-) from the water molecule.
Hydrolysis reaction – It is a chemical process where water (H2O) is used to break down chemical bonds in a compound, splitting it into two or more smaller molecules. It is the reverse of condensation synthesis, normally used to break down polymers into monomers.
Hydrolytic precipitation – The regeneration of hydrochloric spent pickling liquors using hydrolytic precipitation technology involves the process of vapour distillation under evaporative hydrolysis conditions at temperatures as high as 250 deg C. When there are no other chloride salts present, hydrolytic distillation process proceeds to completion at around 175 deg C. However, when magnesium chloride is present, a higher temperature is needed for the hydrolytic distillation process be completed.
Hydrolytic resistance – It is the ability of a material to withstand degradation when exposed to water or aqueous solutions, particularly in acidic and alkaline media.
Hydrolytic stability – It is a hydraulic fluid’s capacity to withstand and resist chemical decomposition when exposed to water. Since water is one of the most common contaminants which a hydraulic fluid regularly comes into contact with, hydrolytic stability is an important characteristic.
Hydro-mechanical coupling – It is the interaction between fluid pressure (hydraulic) and stress / deformation (mechanical) in porous or fractured materials. It describes how changes in fluid pressure affect rock strength and deformation, and conversely, how rock deformation changes pore space and flow permeability. It is critical in geology for modeling geothermal energy, oil extraction, and landslides.
Hydro-mechanical machines – These devices which combine hydraulic components (utilizing pressurized fluid) and mechanical components (gears, linkages, levers) to transmit power and perform work. They function by converting hydraulic energy into mechanical energy or vice versa, frequently leveraging Pascal’s Law to generate high force multiplication from a relatively small input.
Hydro-mechanical press – It is a press in which the moulding forces are created partly by a mechanical system and partly by a hydraulic system.
Hydro-metallurgical process – It is a method of extracting and purifying metals from ores, concentrates, and waste materials using aqueous solutions (water-based) rather than high-temperature heat. It involves chemical dissolution (leaching), purification / concentration, and metal recovery to produce high-purity metals efficiently, typically at lower emissions than smelting.
Hydro-metallurgical processing – It is a method used to extract and purify metals from crushed ore or concentrated minerals through steps such as extraction, concentration, purification, and recovery. This processing technique is normally applied to metals like copper, gold, and zinc.
Hydro-metallurgy – It is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. It is the industrial winning or refining of metals using water or an aqueous solution. Hydro-metallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques which complement hydro-metallurgy are pyro-metallurgy, vapour metallurgy, and molten salt electro-metallurgy. Hydro-metallurgy is typically divided into three general areas namely leaching, solution concentration and purification, and metal or metal compound recovery.
Hydrometeor – It is any liquid or solid water particle formed by condensation or sublimation in the atmosphere (clouds, rain, snow, hail, fog) or deposited / blown at the earth’s surface. They are analyzed for their impact on remote sensing, radar attenuation, communication systems, and structural loads (e.g., roof snow, icing).
Hydrometer – It is an instrument used to measure the specific gravity (relative density) of liquids, operating on Archimedes’ principle of buoyancy. It consists of a weighted, sealed glass tube which sinks deeper in lighter liquids and shallower in denser liquids, with a calibrated scale indicating density.
Hydrometry – It is the monitoring of the components of the hydrological cycle including rainfall, ground-water characteristics, as well as water quality and flow characteristics of surface waters. It essentially involves the measurement and analysis of water in natural water bodies and hydraulic systems.
Hydronic heating system – It is a method which uses heated water or a glycol-water solution as the heat-transfer medium, circulating it through a closed piping network to transfer thermal energy from a source (boiler, heat pump) to radiators, convectors, or underfloor piping for space heating.
Hydrophilic – It means tending to absorb water. It also means tending to concentrate in the aqueous phase.
Hydrophilic coating – It is a surface treatment designed to attract water, forming a lubricious, gel-like layer upon contact with moisture. It is used mainly to improve lubricity and reduce friction.
Hydrophilic glass – It is a material with high water affinity, defined by a water contact angle approaching 0-degree to 90-degree (typically below 5-degree for super-hydrophilic). It causes water to spread into a thin, uniform sheet rather than droplets. It is used for self-cleaning, anti-fogging, and anti-static applications.
Hydrophilic groups – These are polar or ionic functional groups (e.g.-OH-COOH-NH2) which possess a high affinity for water, promoting solubility, swelling, or wetting in materials. They are important al for designing polymers surfactants, and membranes which interact with moisture, enable drug delivery, or manage surface energy.
Hydrophilic interaction chromatography – It is a liquid chromatography technique for separating polar, ionic, and hydrophilic analytes using a polar stationary phase (e.g., silica, diol) and a water-miscible organic mobile phase (e.g., acetonitrile). It operates similarly to normal-phase chromatography but with reversed-phase-type eluent, where retention increases with analyte polarity.
Hydrophilicity – It refers to a material surface’s high affinity for water, characterized by a static water contact angle of less than 90-degree (typically below 10-degree for super-hydrophilic). It indicates a strong interaction, such as hydrogen bonding, allowing water to spread rapidly across surfaces, which is critical for anti-fogging, self-cleaning, and membrane applications.
Hydrophilic membrane – It is a water-attracting porous material designed to readily wet, absorb, or pass water while resisting oily / organic foulants. Defined by low water contact angles (typically below 90-degree, frequently below 60-degree), these materials are used in reverse osmosis, and water filtration, to maximize water flux and minimize fouling.
Hydrophilic nature – It defines a substance’s affinity for water, characterized by its ability to dissolve in, mix with, or be wetted by water. These ‘water-loving’ materials are typically polar or ionic, forming hydrogen bonds with water molecules, and are frequently identified by a low water contact angle (less than 90-degree).
Hydrophilic pervaporation – It is a membrane-based, liquid-separation process which preferentially removes water from organic mixtures (such as alcohol dehydration) by sorbing it into a dense hydrophilic membrane, diffusing it through, and evaporating it on the permeate side under low pressure. It is highly energy-efficient compared to distillation.
Hydrophilic silica – It is a high-purity, synthetic, amorphous silicon di-oxide (SiO2) powder characterized by a water-loving surface covered in silanol (Si–OH) groups. It is produced through high-temperature hydrolysis of chlorosilanes, creating a fine, white powder that readily wets, disperses in water, and acts as a thickening or anti-caking agent.
Hydrophilic surface – It is a ‘water-loving’ material surface which has a high affinity for water, causing water droplets to spread out and wet the surface rather than bead up. These surfaces typically have a water contact angle of less than 90-degree, and frequently feature high surface energy, polar functional groups (such as hydroxyl or carboxyl), or hydrophilic coatings.
Hydrophobic – It means tending to repel water. It also means lacking an affinity for water. It refers to surfaces which tend not to adsorb water or be wetted by water, frequently characterized by large contact angles higher than 90-degree, indicating low wettability.
Hydrophobic catalyst – It is a material with a water-repelling surface (typically a contact angle above 90-degree) designed to operate in wet environments by preventing water from blocking its active sites. These catalysts improve efficiency and longevity in organic synthesis and syngas conversion by resisting water-induced deactivation and facilitating organic substrate access.
Hydrophobic cement – This cement is produced by mixing certain materials (stearic acid, oleic acid etc. by 0.1 % to 0.4 %) with ordinary Portland cement before grinding, to form water repellent layer around the cement particles. The water repellent film formed around each grain of the cement reduces the deterioration of the cement during the long storage, transportation and unfavourable environment. Water repellent film formed also improves the workability. The water repellent film is removed during the mixing process with water.
Hydrophobic contaminants – These are water-repelling, non-polar substances which do not dissolve easily in water, tending instead to accumulate in sediments, and soil organic matter. These persistent organic pollutants (POPs), such as poly-chlorinated biphenyls (PCBs), and poly-cyclic aromatic hydro-carbons (PAHs), pose substantial environmental risks.
Hydrophobic effect – It is the thermodynamic tendency of nonpolar substances to aggregate in aqueous solutions to minimize their surface area contact with water, driven largely by the increase in entropy of the surrounding water molecules. This principle is important for self-assembly, surface modification (e.g., creating super-hydrophobic coatings).
Hydrophobic force – It is the attractive interaction which drives nonpolar molecules and surfaces to aggregate in aqueous solutions, minimizing their contact with water. It is a fundamental, entropy-driven process. Hydrophobic forces are important in the formation of nano-structures through the cooperation of hydrophobic interactions and hydrogen bonding.
Hydrophobic fraction – It refers to the portion of organic matter, molecules, or materials which possess little to no affinity for water, causing them to repel water or remain insoluble in aqueous environments. It is normally composed of nonpolar, nonionic, or aromatic substances, such as humic substances in water, which tend to adsorb onto materials.
Hydrophobic group – it is a non-polar, water-repelling region of a molecule which does not readily interact with or dissolve in water. Typically composed of hydrocarbon chains or aromatic rings, these ’water-fearing’ groups aggregate together in aqueous environments to avoid water.
Hydrophobic interactions – These are the tendency of nonpolar substances to aggregate in aqueous solutions to minimize contact with water, driven by an increase in entropy. These interactions are fundamentally, an entropy-driven process where water molecules exclude nonpolar molecules.
Hydrophobic particle – It is a nonpolar substance which repels water (‘water-fearing’) and does not easily mix, dissolve, or interact with water molecules. These particles tend to aggregate together in water to minimize contact, frequently forming droplets.
Hydrophobic pervaporation – It is a membrane-based separation process which selectively removes small quantities of organic compounds, such as volatile organic compounds (VOCs), solvents, from aqueous solutions using a water-repelling (hydrophobic) membrane. It operates by preferentially sorbing organic molecules and allowing them to evaporate through the membrane, driven by a vacuum on the permeate side.
Hydrophobic properties – These properties define materials which actively repel water, characterized by surfaces with low wettability and a water contact angle higher than 90-degree. These materials are frequently non-polar or textured at the nanoscale, prevent water adhesion. These properties describe the tendency of nonpolar substances to repel water, minimize contact with it, and aggregate in aqueous environments. These properties are necessary for creating water-resistant, self-cleaning, or specialized functional surfaces, and facilitate corrosion resistance.
Hydrophobic recovery – It is the time-dependent process where a previously treated hydrophilic (water-loving) surface, typically a polymer, reverts to its original hydrophobic (water-repelling) state. It involves the inward diffusion of polar groups and the reorientation of polymer chains, frequently reducing surface energy after treatments like plasma activation.
Hydrophobic silica – It is a type of silicon di-oxide (SiO2) nano-particle which has been surface-treated with silane coupling agents (e.g., alkyl or poly-dimethyl-siloxane chains) to become water-repellent. It changes from hydrophilic to hydrophobic, providing excellent water repellency, thickening, and anti-caking properties in coatings, paints, cosmetics, and plastics.
Hydrophytic – In relation to vegetation, these are the plants which grow in water or in saturated soils that are periodically deficient in oxygen as a result of high-water content.
Hydropower – It is a renewable energy source which generates electricity by using the force of moving or falling water to turn turbines. It converts the kinetic energy of rivers or water released from reservoirs (dams) into electricity. It is a sustainable, reliable, and low-cost energy source. It is considered a sustainable, mature technology.
Hydropower construction – It refers to the planning, engineering, and building of infrastructure—such as dams, reservoirs, and powerhouses—designed to harness the energy of moving water to generate electricity. It involves creating systems which transform kinetic energy into power through turbines and generators, normally involving long-term, large-scale civil engineering projects.
Hydropower development – It is the planning, design, construction, and operation of facilities which convert the kinetic or potential energy of flowing or falling water into renewable electrical energy. It involves utilizing rivers, streams, or reservoirs, frequently through dams, to drive turbines and generators, providing a sustainable, reliable, and low-emission energy source.
Hydropower engineering – It is a specialized field focused on designing, constructing, and managing systems which convert the kinetic and potential energy of flowing or falling water into electrical energy. It integrates disciplines like hydrology, geology, and mechanical engineering to build sustainable power plants, dams, and turbines while addressing environmental and economic impacts.
Hydropower flexibility – It is the ability of hydropower systems to rapidly adjust electricity generation—by starting, stopping, or ramping production up / down, to match fluctuating demand and variable renewable energy supply. It ensures grid stability through storage capabilities (reservoirs / pumped storage) and quick, high-power output.
Hydropower infrastructure – It refers to the engineered, physical systems designed to harness the kinetic energy of moving water to generate renewable electricity. It includes large-scale civil structures like dams and reservoirs for water storage, as well as penstocks, turbines, and generators that convert hydraulic potential energy into power.
Hydropower plant – It is a renewable energy facility which converts the potential and kinetic energy of flowing or falling water into electrical energy. Using turbines and generators, these plants typically utilize dams to store water in a reservoir, allowing it to flow through a penstock to turn turbine blades.
Hydropower reservoir – It is a large, artificial lake created behind a dam to store, manage, and regulate water flow for electricity generation. It acts as a battery, holding water at a high elevation (hydraulic head) to create potential energy, which is released on demand to turn turbines.
Hydropower tunnels – These are underground conduits, shafts, and galleries designed to transport water for electricity generation. They typically connect water intake structures, such as dams or reservoirs, to a power station. These tunnels are crucial for managing water flow, providing pressure control, and optimizing energy conversion in both conventional and pumped-storage hydropower projects.
Hydro-processing – It is a catalytic refinery process which uses hydrogen at high temperatures and pressures to upgrade, clean, and convert hydrocarbon feedstocks. It combines hydrotreating (removing contaminants like sulphur, nitrogen, and oxygen) and hydrocracking (breaking down heavy molecules) to produce cleaner, high-quality, stable fuels and lubricants.
Hydro-refining of crude benzol – Hydro-refining treatment method of crude benzol is based on the hydrogenation reactions of sulphur and unsaturated compounds admixtures. During the hydro-refining of crude benzol, treatment of crude benzol is carried out in the presence of hydrogen gas over a catalyst under pressure. Hydrogen gas is used as a hydrogenation agent. Hydrogen gas is separated from coke oven gas by pressure swing adsorption (PSA) method. The process parameters (temperature, pressure, hydrogen / raw materials molar ratio, contact time, catalyst type) are selected in such a way so to ensure almost hydrogenation of entire quantities sulphur, unsaturated, oxygen-containing and nitrogen-containing impurities but by avoiding the hydrogenation reactions of aromatic hydrocarbons. Hydrogen gas is mainly consumed for destructive hydrogenation of thiophene and carbon sulphide (CS2) and hydrogenation of cyclopentadiene and styrene. Initially, the crude benzol is purified from sulphur, non-aromatics and other compounds to produce BTXS (benzene, toluene, xylene, and solvent naphtha) raffinate for processing in the extractive distillation unit. This unit consists of three sections namely (i) de-fronting section, (ii) reaction section, and (iii) purification section.
Hydrosizer – It is also known as an upward flow classifier. It is a piece of equipment which is used to separate materials based on their size and density, mainly in mining and aggregate processing. It works by using a controlled upward current of water to create a fluidized bed, where particles of different sizes and densities settle at different rates, allowing for separation. Hydrosizers utilize the principle of hindered settling, where the upward flow of water opposes the downward settling of particles, making it easier to separate particles of similar size and density.
Hydrostatic axis – It is a line in principal stress space (s1 = s2 = s3) representing a state of purely hydrostatic stress (equal pressure in all directions). It is used in mechanics to define the location of zero shear stress, where the hydrostatic component of stress causes volume changes (volumetric strain) without changing shape.
Hydrostatic bearing – It is a bearing in which the solid bodies are separated and supported by a hydrostatic pressure, applied by an external source, to a compressible or incompressible fluid interposed between those bodies.
Hydrostatic behaviour – It refers to the study of fluids (liquids or gases) at rest and the pressure they exert on immersed bodies. It focuses on pressure distribution, which increases with depth (pressure = density x gravity x depth), and buoyancy, acting perpendicularly to surfaces. Key principles include equilibrium, where no relative motion exists between fluid layers.
Hydrostatic calculations – These calculations determine the pressure, forces, and stability of fluids at rest, mainly using the formula (pressure = density x gravity x depth). These computations are necessary for calculating pressure at depth in tanks and dams.
Hydrostatic coextrusion – It is an advanced metal-forming engineering process in which two or more distinct materials (e.g., a core and a shell) are simultaneously extruded through a die, with the entire assembly surrounded by a high-pressure, viscous fluid medium. It combines the principles of coextrusion (combining different materials for specialized properties) and hydrostatic extrusion (using fluid pressure to eliminate container-wall friction).
Hydrostatic compacting – It is a special case of isostatic pressing which uses a liquid such as water or oil as a pressure transducing medium and is hence limited to near room-temperature operation.
Hydrostatic extrusion – It is a method of extruding a billet through a die by pressurized fluid instead of the ram used in conventional extrusion. In the hydrostatic extrusion, the container is filled with a fluid. Extrusion pressure is transmitted through the fluid to the billet. Friction is eliminated in this process since there is no contact between billet and container wall. Brittle materials can be extruded by this process. Highly brittle materials can be extruded into a pressure chamber. Higher reductions are possible by this method. Pressure involved in the process can be as high as 1,700 MPa. Pressure is limited by the strength of the container, ram, and die materials. Vegetable oils such as castor oil are used. Normally hydrostatic extrusion process is carried out at room temperature.
Hydrostatic force – It is the total force exerted by a fluid at rest on a submerged surface, resulting from pressure increasing with depth (force = pressure x area). It acts through the centre of pressure, which is below the surface’s centroid. Key factors include fluid density, gravitational acceleration, depth, and area.
Hydrostatic head – t is a measure of water pressure expressed as the vertical height (in millimeters) of a column of water. It represents the pressure exerted by a fluid at a given point, frequently used to determine the waterproofing capability of fabrics or materials, where a higher rating means more resistance to leakage.
Hydrostatic loading – It is the pressure exerted by a stationary fluid (liquid or gas) on an immersed object or containing wall, increasing linearly with depth because of the gravity. It acts normal (perpendicular) to the surface, determined by the formula (density x gravity x depth).
Hydrostatic lubrication – It is a system of lubrication in which the lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a fluid film.
Hydrostatic modulus – It is the measure of resistance to change in volume; the ratio of hydrostatic stress to the corresponding unit changes in volume.
Hydrostatic mould – It is a sealed flexible mould made of rubber, a polymer, or pliable sheet made from a low melting point metal such as aluminum.
Hydrostatic pressing – It is a special case of isostatic pressing which uses a liquid such as water or oil as a pressure transducing medium and is hence limited to near room-temperature operation.
Hydrostatic pressure – It is the pressure exerted by a fluid (liquid or gas) at rest, caused by the force of gravity acting on the weight of the fluid above a specific point. It increases linearly with depth, is independent of container shape, and acts equally in all directions.
Hydrostatic pressure measurement – The hydrostatic pressure is the force exerted by a column of water above a reference point. The measured pressure is proportional to the height. The measuring cell operates as a differential pressure meter in the sense that the minus side is open to the atmospheric pressure. This pre-pressure is applied to both sides of the diaphragm and is, thus, self-cancelling. As the transmitter is mounted to the side wall, the zero of the transmitters can be adjusted such that the lower range value is based on the channel floor. Naturally, communication between the device and modern process control systems is possible through an interface or a fieldbus coupler. The measuring ranges lie between 0.01 kilogram per square centimeter and 102 kilograms per square centimeter. The diaphragm flush-mounted to the inner wall of the flume is unaffected by deposits and contamination.
Hydrostatics – It is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and ‘the pressure in a fluid or exerted by a fluid on an immersed body’. The word ‘hydrostatics’ is sometimes used to refer specifically to water and other liquids, but more frequently it includes both gases and liquids, whether compressible or incompressible. It encompasses the study of the conditions under which fluids are at rest in stable equilibrium. It is opposed to fluid dynamics, the study of fluids in motion. Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing, transporting and using fluids.
Hydrostatic seal – It is a seal incorporating features which maintain an interfacial film thickness by means of pressure. The pressure is provided either by an external source or by the pressure differential across the seal. The interfacial pressure profile of a seal face is normally speed-dependent, while the interfacial pressure profile of the hydrostatic seal is not speed-dependent.
Hydrostatic stress – It also known as isotropic stress or volumetric stress. It is a uniform, compressive, or tensile state of stress acting equally in all directions within a material, analogous to pressure in fluid mechanics. It is the general three-dimensional state of stress acting on a body consists of three independent shear stresses and three independent normal stresses. Defined as the mean of normal stresses, Sh = (Sx + Sy + Sz)/3, it causes volume changes (volumetric strain) but no distortion or shear. Constant volume materials cannot permanently deform when the loading conditions create a stress state that is purely hydrostatic. Hence, the presence of a hydrostatic stress is important for understanding of brittle fracture.
Hydrostatic system – It is a branch of fluid mechanics studying fluids at rest (or in equilibrium) and the pressure / forces they exert, mainly based on Pascal’s law and Archimedes’ principle. It focuses on how pressure increases with depth in confined or unconfined liquids and gases. It refers to pressurized, closed-loop fluid power transmission.
Hydrostatic tension – It consists of three equal and mutually perpendicular tensile stresses.
Hydrostatic test – It is a strength and tightness test of a closed pressure vessel by water pressure. In case of valves, it is a test in which a valve is filled with water and pressure tested. As per ISO 14313 hydrostatic tests on a valve are (i) hydrostatic shell test which is done at a pressure 1.5 times the design pressure, and (ii) hydrostatic seat test which is done at a pressure 1.1 times the design pressure.
Hydrostatic test condition – It is a quality assurance procedure where a vessel or piping system is filled with water (or another liquid), purged of air, and pressurized, typically 1.25 times to 1.5 times the design pressure, to verify structural integrity, strength, and tightness against leaks.
Hydrostatic testing – It is a pressure testing method which utilizes water to verify the integrity of equipment and pipelines and detect potential leaks. It is the main method used to test for leaks and assess the structural integrity of meter skids, compressed gas cylinders, boilers, tubing, pipelines and other pressurized vessels. It’s performed by filling the system with water, pressurizing it up to a level higher than ‘maximum allowable working pressure’ (MAWP), and monitoring for visible and / or measurable leaks during a specified amount of time.
Hydrostatic transmission – It is a method of transmitting energy using hydraulic fluid, typically involving a variable displacement pump and a motor which convert mechanical energy into pressure and back, allowing for an infinitely variable transmission without the need for a starting clutch.
Hydro storage – It is a method of storing electrical energy by pumping water from a lower level to a higher reservoir, hence converting the energy into potential energy.
Hydro testing – It is a non-destructive, important quality control process used to verify the structural integrity and leak-tightness of components like pipelines, pressure vessels, boilers, and gas cylinders. It involves filling the system with water (frequently dyed for visibility), removing air, and pressurizing it, normally to 1.25 times to 1.5 times the operating pressure, to ensure it can safely handle its intended, higher-than-normal load.
Hydro-thermal – It is relating to hot fluids circulating in the Earth’s crust. It is also the name given to geological processes associated with heated or relating to heat derived from within the Earth, commonly related to igneous intrusions.
Hydro-thermal acid regeneration process – Hydro-thermal acid regeneration process is relatively newer technology. It replaces the directly fired furnace and gas / liquid absorption by an alternative process route consisting of oxidation and hydrolysis. Formation of ferric oxide takes place in liquid phase which reduces the consumption of heat energy. The concentration of regenerated acid is equal to waste acid total hydro-chloric acid concentration. This concentration of regenerated acid can be increased to a level higher than 30 % by using a pre-concentrator. The iron oxide quality produced by this process is comparable to pyro-hydrolytic processes in terms of the chloride ion contamination. However specific surface of particles is adjustable to much higher figures by tuning of the hydrolysis conditions.
Hydrothermal alteration – It the mineralogical, chemical, and textural modification of rocks caused by hot, aqueous, circulating fluids (100 deg C to 700 deg C) interacting with the rock mass. This process causes substantial geotechnical issues by altering rock strength, porosity, and permeability, frequently leading to slope instability, tunneling hazards, and foundation problems.
Hydrothermal alteration of biotite – It is an important geological process in which hot, chemically active fluids (typically 200 deg C to 400 deg C) interact with biotite, leading to the dissolution of primary mica and the precipitation of secondary minerals, most commonly chlorite. This process is characterized by the removal of potassium (K+) and the addition of iron (Fe2+) and magnesium (Mg2+) to form chlorite, frequently accompanied by mineral volume changes which can create microfractures in the rock.
Hydrothermal iron ores – These are iron ore deposits formed by hot solutions which transported iron and replaced rocks of favorable chemical composition with iron minerals to form irregular ore bodies. In these deposits, iron frequently occurs as siderite (FeCO3) or sometimes as oxides.
Hydrothermal liquefaction – It is a thermo-chemical engineering process which converts wet biomass (50 % to 90 % moisture) into high-energy-density liquid bio-crude, using water at subcritical conditions (250 deg C to 380 deg C temperature and 5 mega-pascals to 25 mega-pascals pressure) as both solvent and reactant. It operates without pre-drying, breaking down macro-molecules through hydrolysis and depolymerization.
Hydrothermal liquefaction process – It is the thermo-chemical conversion of different biomass feedstocks in hot, compressed water under sub-supercritical conditions, producing a high-value liquid product known as bio-oil. This process typically operates at temperatures of 250 deg C to 380 deg C and pressures of and 5 mega-pascals to 25 mega-pascals, facilitating the breakdown of biomass into smaller fragments.
Hydrothermal metallurgy – It is an advanced branch of extractive metallurgy which uses high-temperature, high-pressure aqueous chemistry to extract and recover metals from ores, concentrates, or residues. Operating under saturated steam pressure, this process frequently utilizes autoclaves for leaching and refining, providing an environmentally friendly alternative to pyrometallurgy for producing high-quality materials.
Hydrothermal pre-treatment – It is also called liquid hot water treatment. It is a process utilizing water at high temperatures (150 deg C t0 230 deg C) and pressures to break down biomass, such as hemicellulose, without chemicals. It improves biodegradability, and improves, for example, biogas production efficiency.
Hydrothermal processes – These processes are extractive techniques which use high-temperature (frequently 100 deg C to 300 deg C plus), high-pressure, aqueous solutions in sealed vessels (autoclaves) to dissolve, refine, or crystallize metals and minerals. These methods facilitate rapid processing of materials, such as separating copper from ore, by accelerating geo-chemical reactions.
Hydrothermal process for pelletizing iron ore – It is a specialized metallurgical technique used to agglomerate fine iron ore particles into hard, durable pellets, frequently at lower temperatures than conventional high-temperature sintering or induration. Instead of relying solely on high-temperature sintering (1,200 deg C to 1,350 deg C), this process uses high pressure and temperature, frequently in the presence of water, to create binding mechanisms (e.g., in COBO or hydrothermal hardening processes).
Hydrothermal processing – It is a technique which uses high-temperature, high-pressure aqueous solutions in a sealed system (autoclave) to crystallize, dissolve, or transform materials. It acts as an, frequently environmentally friendlier, method to extract, refine, or synthesize metal compounds and nano-structures, operating above 100 deg to achieve high purity and homogeneity.
Hydrothermal reservoir – It is a subsurface, permeable rock formation containing substantial, trapped high-temperature temperature geofluid, which can be liquid, steam, or a mixture (above 100 deg C to 200 deg C). It is defined by the presence of a natural heat source, fluid supply, and an impermeable caprock which allows for economic extraction of thermal energy for electricity or heating, normally at depths less than 5 kilometers.
Hydrothermal synthesis – It is a method for producing highly crystalline, pure materials, including nano-particles, ceramics, and crystals, by treating precursors in an aqueous solution inside a sealed, high-pressure, and high-temperature autoclave. It uses water as a reaction medium at temperatures normally above 100 deg C and pressures above 0.1 mega-pascal to control chemical reactivity and morphology.
Hydrothermal waves – These are a type of supercritical, oscillatory instability which occurs in liquids subjected to thermal gradients, particularly within the context of Marangoni flow (surface-tension-driven convection). They are characterized as traveling or rotating thermal perturbations (hot / cold spots) which propagate along the free surface of a fluid, frequently appearing as a sequence of vortices.
Hydro-thermolysis – This is a catalytic process which converts algal or oil plant feedstock into jet fuel through hydrothermal liquefaction, occurring at mild temperatures (250 deg C to 380 deg C) and pressures (5 mega-pascals to 30 mega-pascals) in the presence of water, enabling high-energy efficiency and utilization of wet feedstock.
Hydrotreated vegetable oil – It is a paraffinic diesel derived from biomass, categorized as a renewable diesel which can be used in conventional vehicles without blending. It is characterized by the absence of oxygen, aromatics, and sulphur, and shows superior properties compared to biodiesel, including a higher cetane number and better oxidative stability.
Hydrotreating – It is a catalytic, high-pressure, high-temperature refinery process which uses hydrogen to remove contaminants, mainly sulphur, nitrogen, oxygen, and metals, from petroleum feedstocks (naphtha to heavy vacuum gas oils). Key objectives include improving fuel quality, meeting environmental standards (reducing sulphur oxides, SOx, nitrogen oxides, NOx), and protecting downstream catalysts from poisoning.
Hydrotrope – It is a compound which increases the aqueous solubility of insoluble or poorly soluble organic compounds (solutes) by a factor of 100 to 1,000 or more, typically by using relatively high concentrations (0.1 % to 15 %). Unlike surfactants, which form micelles at low concentrations, hydrotropes have a shorter, more compact, and bulkier hydrophobic moiety (frequently an aromatic ring) paired with a strongly hydrophilic ionic head. They are often described as amphiphilic coupling agents which do not form classical micellar structures.
Hydrous pyrolysis – It is a thermo-chemical process which at decomposes organic material in the presence of water at sub-critical conditions (180 deg C to 280 deg C and high pressure). It acts as a green, wet-waste conversion method, breaking down biomass / waste into solid hydrochar, synthetic oil, and gas, specifically targeting high-moisture feedstocks.
Hydroxide – It is a diatomic anion consisting of a hydrogen atom covalently bonded to an oxygen atom, having an overall negative charge, with the chemical formula OH-, or any member of a class of organic and inorganic compounds containing a hydroxy group, e.g. sodium hydroxide (NaOH).
Hydroxy – It is a functional group with the chemical formula −OH and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy groups. Both the negatively charged anion OH-, called hydroxide, and the neutral radical ‘OH’, known as the hydroxyl radical, consist of an unbonded hydroxy group.
Hydroxy-ethyl-cellulose – it is a non-ionic soluble cellulose ether, normally used as a viscosity-improving agent in cement-based materials, prepared from alkali cellulose and ethylene oxide. It is characterized by its solubility in water, its ability to improve water retention in mortars, and its role in retarding cement hydration.
Hydroxylated surface – It is an oxide mineral surface which has undergone a reaction with water, resulting in the formation of hydroxyl groups (–OH) and altered surface properties compared to metal-terminated surfaces. These surfaces show increased stability in aquatic environments and can include different configurations of O-containing functional groups.
Hydroxylation – It is a chemical process which introduces one or more hydroxyl groups (-OH) into a compound, transforming C–H bonds into C–OH bonds through oxidation. It increases molecular polarity and water solubility, used in surface engineering (e.g., creating hydrophilic silica) and molecular modification.
Hydroxyl group (–OH) – It is a functional group consisting of one oxygen atom covalently bonded to one hydrogen atom, characterized by high polarity, hydrogen bonding capability, and substantial influence on solubility, reactivity, and acidity in chemical compounds. It acts as a key structural component in alcohols and surface chemistry.
Hydroxyl ion (OH-) – It is a negatively charged, diatomic anion consisting of one oxygen atom covalently bonded to one hydrogen atom, with an extra electron providing a ‘-1’ charge. It acts as an important carrier, base, nucleophile, and catalyst.
Hydroxyl termination – It refers to the saturation of surface dangling bonds on semiconductor materials, such as silicon carbide, by hydroxyl groups, which can improve the material’s functionality and reactivity.
Hydroxypropyl methacrylate – It is a higher methacrylate used to prepare two-part reactive and one-part ultraviolet and visible light curable adhesives, notable for their application in assembling electronic components because of their lower odour and reduced volatility compared to methyl methacrylate.
Hyflon – It is a trade name for a family of high-performance, melt-processable fluoro-polymers, specifically PFA (per- and poly-fluoroalkyl substances) or amorphous copolymers. Engineered for extreme environments, Hyflon offers exceptional chemical inertness, high thermal stability (up to 300 deg C), superior dielectric properties, and low surface energy. It is used for corrosion-resistant linings, semi-conductor components, specialized cables, and advanced membranes.
Hygroscopic – It is the possessing a marked ability to accelerate the condensation of water vapour. It is applied to condensation nuclei composed of salts which yield aqueous solutions of a very low equilibrium vapour pressure compared with that of pure water at the same temperature. It is also pertaining to a substance whose physical characteristics are appreciably altered by effects of water vapour. It is also pertaining to water absorbed by dry soil minerals from the atmosphere with the quantities depend on the physico-chemical character of the surfaces, and increase with rising relative humidity.
Hygroscopic materials – These materials are substances, frequently polymers, such as polyethylene terephthalate (PET) and polyamide (PA), salts, or fibrous materials, such as wood and cotton, capable of attracting, absorbing, and retaining water molecules from the surrounding environment. These materials are characterized by establishing equilibrium moisture content with ambient humidity, leading to physical changes like swelling, shrinking, or reduced strength.
Hygrothermal behaviour – Hygrothermal behaviour of cured composite materials relates to the combined and commonly synergistic effects of moisture absorption and temperature on different physical, chemical and mechanical properties. While effects for polymer-matrix composites can be substantial, thermo-setting matrices are typically much more affected than thermo-plastic matrices. Although hygrothermal effects are irrelevant for meta-land ceramic-matrix composites, their responses as newer materials and as classes are still somewhat uncertain.
Hygrothermal effect – It is the change in properties and shape change of a material (particularly plastics and polymer matrix composites) because of the moisture absorption and temperature change.
Hygrothermal performance – It is the analysis of coupled heat, air, and moisture (hygro-) transfer through building components. It assesses how structures manage vapour diffusion, convection, and storage, aiming to prevent issues like mould, corrosion, and structural degradation while optimizing energy efficiency and indoor comfort.
Hypalon – It is a trade name. It is normally referred to as CSM or chloro-sulfonated polyethylene. It is a high-performance synthetic elastomer / rubber known for exceptional resistance to UV (ultra-violet), weathering, chemicals, and heat. It is engineered for extreme durability, maintaining flexibility between -30 deg C and +130 deg C (up to 150 deg C in some applications). It is widely used for inflatable boats, cable insulation, and chemical-resistant coatings.
Hyperbaric testing – It is a simulated pressure and depth test.
Hyperbolic decline – It refers to a production decline pattern where the decline rate decreases over time, resulting in a curved line on a semi-log plot. It is characterized by three terms namely the initial production (IP) rate, the initial decline rate, and the hyperbolic exponent, with decline rates typically varying between 40 % and 80 % depending on different reservoir and production factors.
Hyperbolic tangent – It is a nonlinear activation function which outputs values ranging from –1 to 1, with its centre at 0, and is mainly used in hidden layers of neural networks to help centre the data, hence facilitating learning for subsequent layers.
Hyperbolic tangent transfer function – It is a function which takes an input and condenses the output into the range of (−1, 1).
Hypercritical activities – These are critical path activities with negative slack time. These activities are created when a sequence of critical path activities leading up to another activity is too long to be completed in the stated duration.
Hyperelastic model – It is a constitutive law used to describe materials which show non-linear, reversible (elastic) behaviour under large strains, frequently up to 700 %. These materials, such as rubber, and elastomers, are normally incompressible and isotropic, with stress-strain relationships derived from a strain energy density function.
Hyper-eutectic alloy – In an alloy system showing a eutectic, it is an alloy whose composition has an excess of alloying element compared with the eutectic composition and whose equilibrium micro-structure contains some eutectic structure.
Hyper-eutectoid alloy – In an alloy system showing a eutectoid, it is an alloy whose composition has an excess of alloying element compared with the eutectoid composition, and whose equilibrium micro-structure contains some eutectoid structure.
Hyper-eutectoid steel – It is a type of carbon steel containing more than 0.76 %–0.83 % carbon (typically up to 2 %), placing it to the right of the eutectoid point on the iron-carbon phase diagram. It is characterized by a micro-structure consisting of pearlite and brittle pro-eutectoid cementite (Fe3C) networks formed at prior austenite grain boundaries during cooling. Its microstructure consists of hard, brittle pro-eutectoid cementite (Fe3C) networks surrounding pearlite grains, making them ideal for high-wear resistance applications such as cutting tools, knives, and bearings.
Hyper-eutectoid tool steels – These are high-carbon ferrous alloys containing more carbon than the eutectoid composition (typically above 0.8 %, normally up to 2 %). These steels are characterized by a microstructure containing excess pro-eutectoid cementite (iron carbide, Fe3C) in addition to pearlite, providing exceptional hardness and wear resistance, which makes them ideal for cutting, forming, and measuring tools.
Hypereutrophic – It is pertaining to a lake or other body of water characterized by excessive nutrient concentrations such as nitrogen and phosphorous and resulting high productivity. Such waters are frequently shallow, with algal blooms and periods of oxygen deficiency.
Hypergeometric distribution – It is a discrete probability distribution used for quality control, determining the likelihood of ‘k’ successes (e.g., non-defective items) in ‘n’ draws from a finite population ‘N’ without replacement. Unlike the binomial distribution, the probability of success changes with each draw as the population composition changes.
Hyperlink – It is a command that attaches a link to an object or text, allowing quick access to additional information, such as a website or a document, when activated. It enables users to connect different elements, facilitating the retrieval of relevant data or resources.
Hyperrectangle – It is a multi-dimensional generalization of a rectangle, defined as a geometric shape in an n-dimensional Euclidean space with edges aligned along coordinate axes. It is a convex, axis-parallel box which defines a closed region bounded by lower and upper limits in each dimension, making it a critical tool for search-space partitioning, optimization, and modeling constraints.
Hypersonic flow – It is the flow regime where the Mach number exceeds 5, characterized by distinct physical phenomena which become important at these higher speeds, particularly in terms of thermal and hydrodynamic boundary layer interactions.
Hypersonic speed – It is the speed which exceeds five times the speed of sound, frequently stated as starting at speeds of Mach 5 and above.
Hyperspectral data – It refers to the detailed spectral information captured by hyperspectral imaging sensors, represented as a data-cube that consists of two spatial dimensions (X and Y) and one spectral dimension (Z). This data allows for the identification and characterization of different materials and objects based on their unique spectral signatures across a wide range of wavelengths.
Hyperspectral images – These are data representations got through hyperspectral imaging technology, which integrates conventional imaging and spectroscopy to capture both spatial and spectral information from objects.
Hyperspectral imagery – It is a type of imaging which captures a wide range of wavelengths across the electromagnetic spectrum, resulting in high-dimensional data cubes which provide detailed spectral information useful for several applications.
Hyperspectral sensor – It is a device which collects data in hundreds of contiguous narrow electro-magnetic bands, allowing for detailed analysis and identification of materials.
Hypersthene – It is an iron-magnesium silicate mineral, formula (Mg,Fe)SiO3, which belongs to the ortho-pyroxene group. It is identified as a rock-forming mineral normally found in basic igneous rocks (such as norite, gabbro, and andesite) and some metamorphic rocks. Although the term ‘hypersthene’ has been discredited by the International Mineralogical Association (IMA) in 1988, with the material now formally classified as ferroan enstatite or within the enstatite-ferrosilite solid solution series, it remains a common term in field geology and engineering descriptions for intermediate iron-rich, orthorhombic pyroxenes.
Hypertext – It is a system for linking related text documents in which any word or phrase can be ‘hyperlinked’ to information related to that word or phrase residing in the same document or in another document. When a hyperlink is activated, the hypertext system retrieves the related information, allowing non-linear navigation through text resources.
Hypertext documents – These are non-linear, digital information structures composed of text, images, and other media which are interconnected by hyperlinks, allowing readers to navigate between related information in a non-sequential, interactive manner. These are defined not merely as text, but as a network of nodes (information units or documents) connected by links.
Hypertext linking – It refers to a non-linear information system where text, images, or other data nodes are connected through hyperlinks. These links allow users to navigate directly between related information, rather than reading in a sequential (linear) order.
Hypertext mark-up language (HTML) – It is the standard mark-up language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is frequently assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript.
Hypochlorite solution – It is an inorganic compound, very frequently sodium hypochlorite (NaOCl), featuring a pale yellow-green colour and a strong chlorine odor. It is widely used as a liquid bleach and powerful disinfectant for water treatment, cleaning, and industrial sanitation. It acts by releasing oxidizing agents which destroy bacteria, viruses, and micro-organisms.
Hypo-eutectic alloy – In an alloy system showing a eutectic, it is an alloy whose composition has an excess of base metal compared with the eutectic composition and whose equilibrium micro-structure contains some eutectic structure.
Hypo-eutectoid alloy – In an alloy system showing a eutectoid, it is an alloy whose composition has an excess of base metal compared with the eutectoid composition and whose equilibrium micro -structure contains some eutectoid structure.
Hypoeutectoid steel – It is a type of carbon steel containing less than the eutectoid quantity of carbon, specifically falling within the range of 0.02 % to 0.76 % – 0.80 % carbon. Upon cooling, it transforms from austenite into a micro-structure containing primary (pro-eutectoid) ferrite and pearlite. It is relatively soft, ductile, and normally used in engineering applications.
Hypoid gear lubricant (hypoid oil) – It is a gear lubricant with extreme-pressure characteristics used in hypoid gears.
Hypoid gears – These gears resemble spiral bevels, but the shaft axes of the pinion and driven gear do not intersect. This configuration allows both shafts to be supported at both ends. In hypoid gears, the meshing point of the pinion with the driven gear is around midway between the central position of a pinion in a spiral-bevel and the extreme top or bottom position of a worm. This geometry allows the driving and driven shafts to continue past each other so that end-support bearings can be mounted. These bearings provide higher rigidity than the support provided by the cantilever mounting used in some bevel gearing. Also adding to the high strength and rigidity of the hypoid gear is the fact that the hypoid pinion has a larger diameter and longer base than a bevel or spiral-bevel gear pinion of equal ratio. Although hypoid gears are stronger and more rigid than the majority of other types, they are one of the most difficult to lubricate because of high tooth-contact pressures. Moreover, the high levels of sliding between tooth surfaces, reduces efficiency. In fact, the hypoid combines the sliding action of the worm gear with the rolling movement and high tooth pressure associated with the spiral bevel. In addition, both the driven and driving gears are made of steel, which further increases the demands on the lubricant. As a result, special extreme pressure lubricants with both oiliness and anti-weld properties are required to withstand the high contact pressures and rubbing speeds in hypoids.
Hypophosphite – It refers to a phosphorus source, specifically ammonium hypophosphite (NH4H2PO2) or sodium hypophosphite (NaH2PO2), used in the synthesis of transition metal phosphides (TMPs) by reacting with metal precursors under heat to liberate phosphine (PH3) gas. Hypophosphite is a compound containing the hypophosphite ion (H2PO2)-, which acts as a powerful reducing agent in electroless nickel plating (ENP) and other surface finishing processes. It is used to reduce metal ions (usually nickel) in solution to a metallic deposit on substrate surfaces without requiring electricity.
Hypophosphite ion (H2PO2)- – It is a colourless, monovalent inorganic anion containing phosphorus in a ‘+1’ oxidation state. It acts as a strong reducing agent, normally used in nickel plating, and serves as the conjugate base of hypo-phosphorous acid. It is also known as phosphinate.
Hypophosphite-reduced cobalt-phosphorus (Co-P) – It is an electroless plating process where cobalt ions in an aqueous solution are reduced to metallic cobalt (Co) on a catalytic substrate using sodium hypophosphite (NaH2PO2) as the reducing agent. This process results in a metallic deposit containing varying amounts of phosphorus, creating a Co-P alloy coating known for its high hardness, very good corrosion resistance, and soft-magnetic properties.
Hypophosphite-reduced cobalt-tungsten-phosphorus (Co-W-P) – It is a type of electroless plating coating (or sometimes electrodeposited alloy) used in surface engineering to produce hard, wear-resistant, and corrosion-resistant thin films. It is mainly used as a high-performance alternative to traditional chromium plating or as a diffusion barrier layer in micro-electronics (micro-electro-mechanical systems, MEMS / ultra-large scale integration, ULSI).
Hypotenuse – It is defined as the longest side of a right-angled triangle, situated directly opposite the 90-degree right angle. It acts as the diagonal connection between the two legs (perpendicular and base) of the triangle, representing the maximum length in that geometric configuration.
Hypothesis – A statistical hypothesis is a hypothesis concerning the value of parameters or form of a probability distribution for a designated population or populations. More generally, a statistical hypothesis is a formal statement about the underlying mechanisms which generated some observed data.
Hypothesis generation – It is the process of formulating potential answers to research questions, which helps clarify the specifics of the experimentation process by identifying variables to be tested and guiding the methods for data collection and analysis.
Hypothesis, null (H0) – It is a fundamental statistical assumption that there is no significant difference, effect, or relationship between variables, or that a new design/process performs the same as the current one. It serves as the default, ‘status quo’ position (e.g., H0 : M = M0) intended to be tested and potentially rejected.
Hypothesis test – Testing of hypotheses is a common part of statistical inference. To formulate a test, the question of interest is simplified into two competing hypotheses, between which one has a choice. The first is the null hypothesis, denoted by H0, against the alternative hypothesis, denoted by H1. For example, with 50 years of annual rainfall totals a hypothesis test can be whether the mean is different in El Nino and ordinary years. Then normally (i) the null hypothesis, H0, is that the two means are equal, i.e., there is no difference, and (ii) the alternative hypothesis, H1, is that the two means are unequal, i.e., there is a difference. If the 50 years are considered as being of three types, El Nino, ordinary, and La Nina then normally (i) the null hypothesis, H0, is that all three means are equal, and (ii) the alternative hypothesis, H1, is that there is a difference somewhere between the means. The hypotheses are frequently statements about population parameters.
Hypothetical distribution – It is a theoretical, assumed, or modeled probability distribution used in statistics to represent how a variable can be distributed within a population, rather than how it is actually observed. It serves as a basis for hypothesis testing, allowing researchers to estimate characteristics, model potential outcomes, and compare them against actual data.
Hypothetical resources – These are undiscovered Resources which are similar to known mineral bodies and which can be reasonably expected to exist in the same producing district or region under analogous geological conditions. If exploration confirms their existence and reveals enough information about their quality, grade, and quantity, they get reclassified as Identified resources.
Hysol – It is a modified epoxy adhesive which is utilized for bonding plastics, such as polyaryl sulfone, in applications involving steel and plastic materials, achieving bond strengths up to 14 mega-pascals when applied on solvent-cleaned surfaces.
Hysteresis – It is a characteristic of a system where its state is history-dependent. As an example, a magnet can have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment frequently form a loop or hysteresis curve, where there are different values of one variable depending on the direction of change of another variable. Hysteresis occurs in ferro-magnetic and ferro-electric materials, as well as in the deformation of rubber bands and shape-memory alloys and several other natural phenomena. In natural systems, it is frequently associated with irreversible thermodynamic change such as phase transitions and with internal friction, and dissipation is a common side effect.
Hysteresis band – It is a defined, intentional control range (an upper and lower threshold) within which a system’s output remains unchanged, preventing rapid, erratic on / off switching (chattering) around a target setpoint. It acts as a buffer zone, improving stability and reducing component wear in thermostats, power converters, and electrical circuits.
Hysteresis comparator – It is also called Schmitt trigger. Itis an electronic circuit utilizing positive feedback to compare an input voltage against two distinct, upper and lower threshold voltages rather than a single reference point. It prevents rapid, unwanted output switching (chattering) caused by noise near the transition point by requiring a significant change in input voltage to flip the output state.
Hysteresis control – It is a feedback control method which maintains a system variable (like voltage, current, or temperature) within a specific band around a target setpoint by switching between two states. It turns the system on / off based on upper and lower thresholds, preventing rapid, inefficient cycling.
Hysteresis, cooling lag – It is the difference between the critical points on heating and cooling because of the tendency of physical changes to lag behind temperature changes.
Hysteresis curve – It is also called B-H loop It is a graph showing the relationship between magnetic flux density (B) and magnetic field strength (H) as a ferromagnetic material is magnetized and demagnetized. It shows that magnetization lags behind the magnetic field, meaning the material retains residual magnetism (retentivity) even when the field is removed.
Hysteresis effect – It refers to the phenomenon where capillary pressure in a porous medium is influenced by the history of saturation changes, indicating that fluid saturation dynamics affect the measurement of capillary pressure.
Hysteresis loop – It characterizes the magnetization / demagnetization characteristics as a function of the applied magnetic field for ferro-magnetic materials. Powder metallurgy products can differ from wrought products because of porosity or impurity traces.
Hysteresis loss – It is a loss of mechanical energy because of the successive deformation and relaxation, measured by the area between the deformation and relaxation stress-strain curves.
Hysteresis (magnetic) – It is the lag of the magnetization of a substance behind any cyclic variation of the applied magnetizing field.
Hysteresis (mechanical) – It is the phenomenon of permanently absorbed or lost energy which occurs during any cycle of loading or unloading when a material is subjected to repeated loading.
Hysteresis phenomenon – It is a phenomenon where a system’s output depends not only on its current input but also on its past history, causing the response to lag behind changes in the input. Frequently shown by a closed loop graph (B -H curve), this history-dependent, non-linear behaviour means the system takes different paths when moving from a state of increase to a state of decrease.
Hysteresis stress – It is also called elastic hysteresis. It is the difference in a material’s stress-strain response between loading and unloading cycles, resulting in a closed loop on a stress-strain graph. It represents internal energy loss, converted into heat, because of molecular friction within the material, such as polymers, rubber, or metals.
Hysteresis voltage – It is the difference between the upper and lower threshold voltages, quantified as Vhys = Vutp − Vltp, where Vutp and Vltp are the upper and lower threshold voltages, respectively.
Hysteretic control – It is a method which regulates the current in an inductor by maintaining it between preset upper and lower boundaries, turning the switch ‘on’ when the current reaches the lower limit and ‘off’ when it hits the upper limit, with adjustments made based on input and output voltages.
Hysteretic heating – It is the generation of heat in polymers during cyclic loading, resulting from the dissipation of strain energy, which causes a temperature increase until the heat generated equals the heat dissipated through conduction, convection, and radiation.
HYTEMP system – It is a pneumatic transport process for the transport of hot direct reduced iron (HDRI). HYTEMP system is based in the concept of pneumatic conveying of bulk materials. The characteristic features of the HYTEMP system include (i) totally enclosed system without minimum losses, (ii) carrier gas is coherent with the hot direct reduced iron, (ii) any non-oxidizing gas can be used as carrier gas (for example, nitrogen, natural gas, or process gas), (iii) no deterioration in the quality of the direct reduced iron (i.e. percent metallization and percent carbon of direct reduced iron) during transport and feeding to the electrical arc furnace, (iv) it is an integrated system and includes continuous and controlled feeding of hot direct reduced iron to the electric arc furnace, (v) gas flow of the carrier gas ranges from 50 cubic meters per ton to 100 cubic meters per ton of direct reduced iron depending on the transport rate, (vi) low power consumption ranging from 4 kilowatt hour per ton of direct reduced iron to 6 kilowatt hour per ton of direct reduced iron, depending on the transport rate, (vii) low nitrogen consumption of around 6 cubic meters per ton of direct reduced iron for the complete operation, transport, and continuous feeding to the electric arc furnace, (viii) flexible configuration to match the space available in the steel melting shop with an arrangement of bins in series or in parallel, (ix) fully automated system for the transporting of hot direct reduced iron from the direct reduction shaft furnace to the steel melting shop and subsequent continuous feeding to the electric arc furnace, (x) the system does not interfere with the material handling, maintenance, or other activities neither at the direct reduction plant nor at the electric arc furnace since the connection between the two units is located at an elevated position, (xi) a system with practically no wearing parts and hence maintenance free (the only wear and tear component is the inflatable seals of the valves), and (xii) a system with very low heat losses. The system operates by using a carrier gas (either an inert gas or the process gas itself) to carry the hot direct reduced iron through a pneumatic pipe to a holding bin above the electric arc furnace.
Hythane – It is a fuel composed of hydrogen (H2) and methane (CH4) which is gaining popularity for its benefits as a car fuel and potential as an alternative to compressed natural gas (CNG). It can be generated from organic waste, making it a more sustainable and economical option compared to fossil-based sources.
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