The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
A Activation loss See overpotential Adsorption Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms (the adsorbate). Alkali In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Alkali anion-exchange membrane An alkali anion-exchange membrane (AAEM) is a semipermeable membrane generally made from ionomers and designed to conduct anions while being impermeable to gases such as oxygen or hydrogen. Alkaline fuel cell Alkaline fuel cell (AFC) also known as the Bacon fuel cell. Alloy An alloy is a solid solution or homogeneous mixture of two or more elements, at least one of which is a metal, which itself has metallic properties. Alternator An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. Alternating current An alternating current (AC) is an electric current which reverses direction cyclically, as opposed to direct current, the direction of which remains constant. Ambient Air The air surrounding a given object or system. Ambient temperature Ambient temperature is the temperature within enclosed space. Ampere The ampere, in practice often shortened to amp, (symbol: A) is a unit of electric current, or amount of electric charge per second. Anion A negatively charged ion; an ion that is attracted to the anode. Anode An anode is an electrode through which electric current flows into a polarized electrical device. Aqueous phase reforming APR is the production of hydrogen from biomass-derived oxygenated compounds (such as glycerol, sugars and sugar alcohols). Artificial membrane An artificial membrane, also called a synthetic membrane, is a membrane prepared for separation tasks in laboratory and industry. Atmospheric pressure Atmospheric pressure is the pressure at any given point in the Earth's atmosphere. Atom The atom is the smallest unit of an element that retains the chemical properties of that element. An atom has an electron cloud consisting of negatively charged electrons surrounding a dense nucleus. The nucleus contains positively charged protons and electrically neutral neutrons. Autothermal reforming Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form syngas. Auxiliary power unit An auxiliary power unit (APU) is a device on a vehicle whose purpose is to provide energy for functions other than propulsion. Availability factor The availability factor of a power plant is the amount of time that it is able to produce electricity over a certain period, divided by the amount of the time in the period.
B
Back pressure Back pressure is the pressure exerted on a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow. Baffle A device or construction used to restrain or regulate, e.g. gas, or a fluid. Balance of plant Balance of plant (BOP) is the infrastructure of a fuel cell, not including the fuel cells. (See also Mechanical Balance of Plant MBOP and Electrical Balance of Plant EBOP). Battery In electronics, a battery is a combination of two or more electrochemical cells which store chemical energy and make it available as electrical energy. Biofuel Biofuel is defined as solid, liquid or gas fuel derived from recently dead biological material and is distinguished from fossil fuels, which are derived from long dead biological material. Biogas Biogas is a gas produced by the biological breakdown of organic matter in the absence of oxygen. Biogas originates from biogenic material and is a type of biofuel. Bioreactor A bioreactor is any device or system that supports a biologically active environment Biosensor A biosensor is a device for the detection of an analyte that combines a biological component with a physicochemical detector component. Bipolar plate A onductive plate in a fuel-cell stack that acts as an anode for one cell and a cathode for the adjacent cell. The plate may be made of metal or a conductive polymer (which may be a carbon-filled composite). The plate usually incorporates flow channels for the fluid feeds and may also contain conduits for heat transfer. See also MEA. Black start A black start is the process of restoring a power station to operation without relying on external energy sources. Beta-alumina solid electrolyte Beta-alumina solid electrolyte (BASE) is a fast-ion conductor material used as a membrane in several types of molten salt electrochemical cell. Boiling point The boiling point of a liquid is the water temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid. Borax Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. British thermal unit The mean British thermal unit (BTU) is 1/180 of the heat required to raise the temperature of one pound (450 g) of water from 32 to 212 °F (0 to 100 °C) at a constant atmospheric pressure. It is about equal to the quantity of heat required to raise one pound of water 1°F (5⁄9°C). Busbar In electrical power distribution, a busbar is the strips of copper or aluminium that conduct electricity within a switchboard, fuel cell, distribution board, substation, or other electrical apparatus.
C
Capacity Capacity is the ability to hold, receive or absorb, or a measure thereof, similar to the concept of volume. Capacity factor The net capacity factor of a power plant is the ratio of the actual output of a power plant over a period of time and its output if it had operated at full nameplate capacity the entire time. Capital cost Capital cost are costs incurred on the purchase of fuel cells, buildings, construction and equipment to be used in the use of fuel cells or the rendering of it. Carbon Carbon (C), an atom and primary constituent of hydrocarbon fuels. Carbon is routinely left as a black deposit on engine parts, such as pistons, rings, and valves, by the combustion of fuel. Carbon black Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon dioxide Carbon dioxide (chemical formula: CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. Carbon dioxide sensor A carbon dioxide sensor (CO2) is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Carbon monoxide Carbon monoxide, with the chemical formula CO, is a colorless, odorless, tasteless yet highly toxic gas. Carbon monoxide detector A carbon monoxide detector is a device that detects the presence of the toxic gas carbon monoxide (CO), a colorless and odorless compound produced by incomplete combustion and lethal at high levels. Carbon paper Carbon paper (originally carbonic paper) is paper coated on one side with a layer of a loosely bound dry ink or pigmented coating, usually bound with wax. Carnot cycle The Carnot cycle is a particular thermodynamic cycle, modeled on the hypothetical Carnot heat engine. Catalysis Catalysis is the process in which the rate of a chemical reaction is increased by means of a chemical substance known as a catalyst. Catalyst A catalyst is a chemical substance that increases the rate of a reaction without being consumed; after the reaction it can potentially be recovered from the reaction mixture chemically unchanged. Catalyst poisoning Catalyst poisoning is the effect that a catalyst can be 'poisoned' if it reacts with another compound that bonds chemically (similar to an inhibitor) but does not release, or chemically alters the catalyst. Catalytic partial oxidation In catalytic partial oxidation (CPOX) the use of a catalyst for partial oxidation reduces the required temperature to around 800°C – 900°C. The choice of reforming technique depends on the sulfur content of the fuel being used. CPOX can be employed if the sulfur content is below 50 ppm. A higher sulfur content would poison the catalyst, so the TPOX procedure is used for such fuels. Cathode A cathode is an electrode through which (positive) electric current flows out of a polarized electrical device. Cation A cation is a positively charged ion. Celsius The degree Celsius (°C) is a designation for specific temperatures on the Celsius scale as well as units of increment to indicate a temperature interval (a difference between two temperatures or an uncertainty). Centimeter A centimetre (American spelling: centimeter, symbol cm) is a unit of length in the metric system, equal to one hundredth of a metre, which is the current SI base unit of length. Centrifugal governor A centrifugal governor is a specific type of governor that controls the speed by regulating the amount of fuel (or working fluid) admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions. Ceramic Ceramics are inorganic non-metallic materials formed by the action of heat. Cermet A cermet is a composite material composed of ceramic (cer) and metallic (met) materials. Chemical thermodynamics In thermodynamics, chemical thermodynamics is the mathematical study of the interrelation of heat and work with chemical reactions or with a physical change of state within the confines of the laws of thermodynamics. Circuit A circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. Circuit diagram A circuit diagram (also known as an electrical diagram, wiring diagram, elementary diagram, or electronic schematic) is a simplified conventional pictorial representation of an electrical circuit. Circulation In fluid dynamics, circulation is the line integral around a closed curve of the fluid velocity. Climate change Climate change is any long-term significant change in the “average weather” that a given region experiences. Cogeneration Cogeneration (also combined heat and power, CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. Combustion Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. Combustion chamber A combustion chamber is the part of an engine in which fuel is burned. Composite material Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure. Compressed hydrogen Compressed hydrogen (CGH2, CH2 or CH2) is the gaseous state of the element hydrogen which is kept under pressure. Compressed natural gas Compressed Natural Gas (CNG) is a fossil fuel substitute for gasoline (petrol), diesel, or propane fuel. Concentration In chemistry, concentration is the measure of how much of a given substance there is mixed with other substances. Condensate Condensate, the liquid phase produced by the condensation of steam or any other gas Condensation Condensation is the change of the physical state of aggregation (or simply state) of matter from gaseous phase into liquid phase. Condenser In systems involving heat transfer, a condenser is a heat exchanger which condenses a substance from its gaseous to its liquid state. Contamination Contamination is the introduction of material that "does not belong there". Coulomb The coulomb (symbol: C) is the SI unit of electric charge. Countercurrent exchange Countercurrent exchange is a mechanism used to transfer some property of a fluid from one flowing current of fluid to another across a semipermeable membrane, conductive material, or free surface (e.g. a liquid–gas absorption or extraction). Cryogenic liquefaction Cryogenic liquification is the process through which gases such as nitrogen, hydrogen, helium, and natural gas are liquefied under pressure at very low temperatures. Current see electric current. Current collector The current collector is the conductive material in a fuel cell that collects electrons (on the anode side) or disburses electrons (on the cathode side). Current collectors are microporous (to allow for fluid flow through them) and lie in between the catalyst/electrolyte surfaces and the bipolar plates.
D
DC-to-DC converter In electronic engineering, a DC-to-DC converter is a circuit which converts a source of direct current (DC) from one voltage level to another. It is a class of power converter. Density The density of a material is defined as its mass per unit volume Desiccant A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. Detection limit In analytical chemistry, the detection limit, lower limit of detection, or LOD (limit of detection), is the lowest quantity of a substance that can be distinguished from the absence of that substance (a blank value) within a stated confidence limit (generally 1%). Dew point The dew point (sometimes spelled dewpoint) is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water. Diffusion Diffusion is part of transport phenomena. Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration by random molecular motion. Direct borohydride fuel cell Direct borohydride fuel cell (DBFC) a subcategory of alkaline fuel cells Direct carbon fuel cell Direct carbon fuel cell (DCFC), a fuel cell that uses a carbonaceous material as a fuel. Direct current Direct current (DC) is the unidirectional flow of electric charge. Direct-ethanol fuel cell Direct-ethanol fuel cell (DEFC) a subcategory of proton-exchange fuel cells where, the fuel, ethanol, is not reformed, but fed directly to the fuel cell. Direct methanol fuel cell Direct methanol fuel cell (DMFC) subcategory of proton-exchange fuel cells where the methanol (CH3OH) fuel is not reformed as in the indirect methanol fuel cell, but fed directly to the fuel cell Dispersion Dispersion, in fluid dynamics is dispersive mass transfer, which is the spreading of mass from areas of high to low concentration Distributed Generation Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources. Doping In semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor in order to change its electrical properties. Downtime Downtime or outage is a period of time or a percentage of a timespan that a system is unavailable or offline. Dry basis It is customary to report the product composition data in steam reforming reactions on a steam free basis (dry basis) since the steam is not a constituent in any of the synthesis gases produced or in the reformed gas when used as a fuel; however, if steam is to be considered in the product composition data as well, then the calculation would be wet basis.
E
Effluent Effluent is an outflowing of water from a natural body of water, or from a man-made structure. Electrical Balance of Plant Electrical Balance of Plant (EBOP), the user interface panel, control equipment, and converting the fuel cell DC power to AC power. Electricity Electricity is any phenomenon resulting from the presence and flow of electric charge. Electrical conductivity Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an electric current. Electrical efficiency The electrical efficiency of an entity (a device, component, or system) in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression), typically denoted by the Greek letter small Eta (η). Electrical insulation An electrical insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself. Electrical resistance Electrical resistance is a ratio of the degree to which an object opposes an electric current through it, measured in Ohms. Electric circuit An electrical circuit is a network that has a closed loop, giving a return path for the current. A network is a connection of two or more components, and may not necessarily be a circuit. Electric current Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere. Electricity generation Electricity generation is the process of converting non-electrical energy to electricity. Electric power conversion In electrical engineering, power conversion has a more specific meaning, namely converting electric power from one form to another. Electrochemistry Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution. Electrochemical cell An electrochemical cell is a device used for generating an electromotive force (voltage) and current from chemical reactions. Electrochemical gas sensor Electrochemical gas sensors are gas detectors that measure the volume of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current. Electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). Electro-galvanic fuel cell Electro-galvanic fuel cell (EGFC)an electrical device used to measure the concentration of oxygen gas in scuba diving and medical equipment. Electroosmotic flow Electroosmotic flow (or Electro-osmotic flow, often abbreviated EOF) is the motion of liquid induced by an applied potential across a capillary tube or microchannel. Electroosmotic flow is an essential component in chemical separation techniques, notably capillary electrophoresis. Electroosmotic pump An electroosmotic pump (EOP), or EO pump, is used for removing liquid flooding water from channels and gas diffusion layers and direct hydration of the proton-exchange membrane in the membrane electrode assembly (MEA) of the proton-exchange membrane fuel cell Electrolysis In chemistry and manufacturing, electrolysis is a method of separating chemically bonded elements and compounds by passing an electric current through them. Electrolyte An electrolyte is any substance containing free ions that behaves as an electrically conductive medium. Electron The electron is a fundamental subatomic particle that carries a negative electric charge. Emission Emission of air pollutants Emission standard Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Endothermic In thermodynamics, the endothermic processes or reactions are those that absorb energy in the form of heat. Energy In physics and other sciences, energy is a scalar physical quantity that is a property of objects and systems which is conserved by nature. Energy is often defined as the ability to do work. Energy carrier An energy carrier is a substance or phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes (ISO 13600). Energy content Amount of energy for a given weight of fuel. see also energy density Energy security Energy security Energy storage Energy storage is the storing of some form of energy that can be drawn upon at a later time to perform some useful operation. Engine An engine is a machine that converts heat energy into mechanical energy. Energy conversion efficiency Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. Energy density Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context, although the latter is more formally specific energy Energy transformation In physics and engineering, energy transformation or energy conversion, is any process of transforming one form of energy to another. Enthalpy In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H, h, or rarely as χ) is a quotient or description of thermodynamic potential of a system that can be used to calculate the "useful" work obtainable from a closed thermodynamic system under constant pressure and entropy. Enthalpy of vaporization The enthalpy of vaporization, (symbol Δ
v H {\displaystyle \Delta {}_{v}H} ), also known as the heat of vaporization or heat of evaporation, is the energy required to transform a given quantity of a substance into a gas. Ethanol Ethanol, also called ethyl alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. Evaporation Evaporation is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor). Exergy In thermodynamics, the exergy of a system is the maximum work possible during a process that brings the system into equilibrium with a heat reservoir. Exergy efficiency Exergy efficiency (also known as the second-law efficiency or rational efficiency) computes the efficiency of a process taking the second law of thermodynamics into account. Exhaust gas Exhaust gas is flue gas which occurs as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel, fuel oil or coal. It is discharged into the atmosphere through an exhaust pipe or flue gas stack. Exothermic In thermodynamics, exothermic processes or reactions are those that release energy, usually in the form of heat but also in the form of light (e.g. explosions), sound, or electricity. Expansion ratio Expansion ratio is used in the context of liquefied and cryogenic substances. The expansion ratio of a substance is the volume of a given amount of that substance in liquid form compared to the volume of the same amount of substance in gaseous form, at a given temperature.
F
Fan A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat), ventilation, exhaust, or any other gaseous transport. Fahrenheit Fahrenheit is a temperature scale. In this scale, the freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point 212 °F Failure mode and effects analysis A failure mode and effects analysis (FMEA) is a procedure for analysis of potential failure modes within a system for classification by severity or determination of the effect of failures on the system. FCEV A Fuel Cell Electric Vehicle is a Fuel cell vehicle that has a battery it can charge from an external source as well as from its on-board fuel cell. FCV Fuel cell vehicle Feedstock purification Feedstock purification, The process of removing poisons like sulfur (S) and chloride (Cl) from the feedstock. Flammability Flammability is the ease with which a substance will ignite, causing fire or combustion. Flammability limit Flammability limits, also called flammable limits, give the proportion of combustible gases in a mixture, between which limits this mixture is flammable. Flash point The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. Float valve A float valve is a mechanical feedback mechanism that regulates fluid level by using a float to drive an inlet valve so that a higher fluid level will force the valve closed while a lower fluid level will force the valve open. Flow battery Flow battery (FB) a form of rechargeable battery in which electrolyte containing one or more dissolved electroactive species flows through a power cell / reactor that converts chemical energy to electricity. Flow measurement Flow measurement is the quantification of bulk fluid movement. It can be measured in a variety of ways. Flue gas Flue gas is gas that exits to the atmosphere via a flue. Flue-gas desulfurization Flue-gas desulfurization (FGD) is the technology used for removing sulfur dioxide (SO2) from the exhaust flue gases. Fluid dynamics Fluid dynamics is the sub-discipline of fluid mechanics dealing with fluid flow: fluids (liquids and gases) in motion. Fluid mechanics Fluid mechanics is the study of how fluids move and the forces on them. (Fluids include liquids and gases.) Fluid mechanics can be divided into fluid statics, the study of fluids at rest, and fluid dynamics, the study of fluids in motion. Flux In the study of transport phenomena (heat transfer, mass transfer and fluid dynamics), flux is defined as the amount that flows through a unit area per unit time. Formic acid Formic acid (systematically called methanoic acid) is the simplest carboxylic acid. Its formula is HCOOH or CH2O2. Formic acid fuel cell Formic acid fuel cell (DFAFC), a subcategory of proton-exchange fuel cells where, the fuel, formic acid, is not reformed, but fed directly to the fuel cell. Fossil fuel Fossil fuels or mineral fuels are fossil source fuels, that is, hydrocarbons found within the top layer of the Earth’s crust. Fouling Fouling is the accumulation of unwanted material on solid surfaces, Frequency changer A frequency changer or frequency converter is an electronic device that converts alternating current (AC) of one frequency to alternating current of another frequency. Fuel Fuel is any material that is burned or altered in order to obtain energy. Fuel cell A fuel cell (FC) is an electrochemical conversion device. Fuel cell poisoning The lowering of a fuel cell's efficiency due to impurities in the fuel binding to the catalyst. See catalyst poisoning. Fuel cell vehicle A fuel cell vehicle is any vehicle that uses a fuel cell to produce its on-board motive power. Fuel efficiency Fuel efficiency, in its basic sense, is the same as thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Fuel efficiency in transportation Fuel efficiency in transportation Fuel processor Device used to generate hydrogen from fuels such as natural gas, propane, gasoline, methanol, and ethanol, for use in fuel cells. Fuel processing system Fuel processing system (FPS) Fuel pump Fuel pump Fusible plug A fusible plug is a threaded metal plug, usually made out of bronze, brass, or gunmetal.
G
Gadolinium doped ceria Gadolinium doped ceria (GDC) – (for SOFC) Gas Fuel gas, such as natural gas, undiluted liquefied petroleum gases (vapor phase only), liquefied petroleum gas–air mixtures, or mixtures of these gases. Liquefied petroleum gases (LPG) as used in this standard, shall mean and include any material which is composed predominantly of any of the following hydrocarbons, or mixtures of them: propane, propylene, butanes (normal butane or isobutane) and butylenes. LP gas–air mixture – Liquefied petroleum gases distributed at relatively low pressures and normal atmospheric temperatures which have been diluted with air to produce desired heating value and utilization characteristics. Natural gas – Mixtures of hydrocarbon gases and vapors consisting principally of methane (CH4) in gaseous form. Gas compressor A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. Gas detector A gas detector is a device which detects the presence of various gases within an area, usually as part of a system to warn about gases which might be harmful to humans or animals. Gas diffusion Mixing of two gases caused by random molecular motions. Gases diffuse very quickly; liquids diffuse much more slowly, and solids diffuse at very slow (but often measurable) rates. Molecular collisions make diffusion slower in liquids and solids. Gas diffusion electrode Gas diffusion electrodes are electrodes with a conjunction of a solid, liquid and gaseous interface, and an electrical conducting catalyst supporting an electrochemical reaction between the liquid and the gaseous phase. Gasification Gasification is a process that converts carbonaceous materials, such as coal, petroleum, or biomass, into carbon monoxide and hydrogen by reacting the raw material at high temperatures with a controlled amount of oxygen and/or steam. Gasoline gallon equivalent Gasoline gallon equivalent (GGE) or gasoline-equivalent gallon (GEG) is the amount of alternative fuel it takes to equal the energy content of one liquid gallon of gasoline. Gibbs free energy In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function) is a thermodynamic potential which measures the "useful" or process-initiating work obtainable from an isothermal, isobaric thermodynamic system. Graphite The mineral graphite, as with diamond and fullerene, is one of the allotropes of carbon. Greenhouse effect Gases in the Earth's atmosphere that contribute to the greenhouse effect, effectively absorbing thermal infrared radiation, emitted by the Earth’s surface Greenhouse gases Warming of the Earth's atmosphere due to greenhouse gases in the atmosphere that allow solar radiation (visible, ultraviolet) to reach the Earth's atmosphere but do not allow the emitted infrared radiation to pass back out of the Earth's atmosphere. Grid connection Grid connection Grid-tied electrical system A grid-tied electrical system, also called Tied to grid or Grid tie system, is a semi-autonomous electrical generation or grid energy storage system which links to the mains to feed excess capacity back to the local mains electrical grid. Grid tie inverter Grid tie inverter Guard bed Guard bed, see guard catalyst bed and liquid-phase guard bed. Guard catalyst bed A guard catalyst bed is a fixed bed of pellets of the same catalytic material, see fixed bed reactor.
H
Half-reaction A half reaction is either the oxidation or reduction reaction component of a redox reaction. Heat exchanger A heat exchanger is a device built for efficient heat transfer from one medium to another, whether the media are separated by a solid wall so that they never mix, or the media are in direct contact. Heat pipe A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces. Heat transfer In thermal physics, heat transfer is the passage of thermal energy from a hot to a colder body. Heating value The heating value (TOTAL) (ΔHc0) is the energy released as heat when a compound undergoes complete combustion with oxygen. (see also Higher heating value (HHV) and Lower heating value) (LHV). Heat of combustion The heat of combustion (ΔHc0) is the energy released as heat when a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. Higher heating value The higher heating value (HHV) (also known as the gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25 °C) once it is combusted and the products have returned to a temperature of 25 °C. High-temperature shift High-temperature shift (HTS), the water gas shift reaction at 350 °C (662 °F) in the presence of a metal-based catalyst (nickel) Hybrid electric vehicle A hybrid electric vehicle (HEV) is a hybrid vehicle which combines a conventional propulsion system with a rechargeable energy storage system (RESS) to achieve better fuel economy than a conventional vehicle. Hydride Hydride is the name given to the negative ion of hydrogen, H−. Hydride ion Aside from electride, the hydride ion is the simplest possible anion, consisting of two electrons and a proton. See also hydrogen anion Hydrocarbon In organic chemistry, a hydrocarbon (HC) is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbon dew point The hydrocarbon dew point (HDP) or (HCDP) is the temperature (at a given pressure) at which the hydrocarbon components of any hydrocarbon-rich gas mixture, such as natural gas, will start to condense out of the gaseous phase. Hydrodesulfurization Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. Hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2. Hydrogen anion The hydrogen anion is a negative hydrogen ion, H−. See also hydride ion. Hydrogen purity Hydrogen purity or hydrogen quality is the lack of impurities in hydrogen as a fuel gas. Hydrogen-rich fuel A fuel that contains a significant amount of hydrogen, such as gasoline, diesel fuel, methanol (CH3OH), ethanol (CH3CH2OH), natural gas, and coal. Hydrogen sulfide sensor A hydrogen sulfide sensor or H2S sensor is a gas sensor for the measurement of hydrogen sulfide in a gas stream.
I
Impurity Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound. Influent Influent Interlock Interlocking is a method of preventing undesired states in a state machine, which in a general sense can include any electrical, electronic, or mechanical device or system. Internal combustion engine An internal combustion engine (ICE) is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. Inverter An inverter is an electrical or electro-mechanical device that converts direct current (DC) to alternating current (AC) Ion An ion is an atom or molecule which has lost or gained one or more valence electrons, giving it a positive or negative electrical charge. Ion exchange Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. Ion-exchange resin An ion-exchange resin is an insoluble matrix (or support structure) normally in the form of small (1–2 mm diameter) beads, usually white or yellowish, fabricated from an organic polymer substrate. Ionomer An ionomer is a polyelectrolyte that comprises copolymers containing both electrically neutral repeating units and a fraction of ionized units Islanding Islanding is the condition of a distributed Generation (DG) generator continuing to power a location even though power from the electric utility is no longer present.
J
K
Kröger–Vink notation Kröger–Vink notation is set of conventions used to describe electrical charge and lattice position for point defect species in crystals. Kilogram The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (known also by its French-language initials “SI”). The kilogram is almost exactly equal to the mass of one liter of water. Kilowatt The kilowatt (symbol: kW), equal to one thousand watts, is typically used to state the power output of engines and the power consumption of tools and machines. Kilowatt hour The kilowatt hour, also written kilowatt-hour (symbol kW·h, kW h or kWh) is a unit of energy.
L
Landfill gas landfill gas (LFG), see biogas. Lanthanum carbonate Lanthanum carbonate is used as a lanthanum source for solid-state production of lanthanum strontium manganite (LSM), primarily for solid oxide fuel cell applications. LH2 See liquid hydrogen. Life cycle assessment A life cycle assessment (LCA, also known as life cycle analysis, ecobalance, and cradle-to-grave analysis) is the investigation and valuation of the environmental impacts of a given product or service caused or necessitated by its existence. Linear regulator In electronics, a linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear region" Liquid liquid is one of the principal states of matter. Liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Liquid–liquid extraction Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. Liquefied natural gas Liquefied natural gas (LNG) is natural gas (primarily methane, CH4) that has been converted to liquid form for ease of storage or transport. Liquefied petroleum gas Liquefied petroleum gas (also called LPG, GPL, LP Gas, or autogas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles Liquefaction In physics, to liquefy (sometimes spelled as "liquify") means to turn something into the liquid state. Liquefaction of gases Liquefaction of gases includes a number of phases used to convert a gas into a liquid state. List of chemical purification methods in chemistry Purification in a chemical context is the physical separation of a chemical substance of interest from foreign or contaminating substances. The following list of chemical purification methods should not be considered exhaustive. Load following power plant A load following power plant is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load profile In electrical engineering, a load profile is a graph of the variation in the electrical load versus time. Lower flammability limit Lower flammability limit (LFL), usually expressed in volume per cent, is the lower end of the concentration range of a flammable solvent at a given temperature and pressure for which air/vapor mixtures can ignite. Lower heating value The lower heating value (also known as net calorific value, net CV, or LHV) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25 °C or another reference state) and returning the temperature of the combustion products to 150 °C. Low temperature shift Low temperature shift (LTS), the water gas shift reaction at 190–210 °C (374–410 °F) in the presence of a metal-based catalyst (nickel).
M
Maintenance, repair and operation cost Maintenance, Repair and Operation Cost or Maintenance, Repair and Overhaul (MRO) is fixing any sort of mechanical or electrical device should it become out of order or broken (repair) as well as performing the routine actions which keep the device in working order (maintenance) or prevent trouble from arising (preventive maintenance). Mass flow sensor A mass flow sensor (MAF) responds to the amount of a fluid (usually a gas) flowing through a chamber containing the sensor. Maximum allowable operating pressure Maximum allowable operating pressure (MAOP) is the wall strength of a pressurized c