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Dictionary of Energy

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freshness index


fuel cycle analysis

rains or rapidly melting snow. 2. any small, clear freshwater stream.

freshness index HVAC. a sensory index indicating a subjective assessment of the purity of indoor air by building occupants.

Fresnel cooker Solar. a type of solar cooker that uses a parabolic reflector (Fresnel lens) to concentrate and transfer solar radiation onto a baking tray or cooking pot.

Fresnel lens Solar. an optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point. [Invented by French physicist Augustin Fresnel, 1788–1827.]

friable Materials. easily broken into small pieces. Thus, friability.

friction Physics. a force that opposes the relative motion of two material surfaces that are in contact with one another; the direction of the force on each body is opposite to the direction of its motion relative to the other body.

friction head Physics. 1. the amount of reduction in the head (height under pressure) of a fluid, due to the friction between the fluid and its container and also to the intermolecular interaction. 2. Hydropower. the resistance that must be overcome by a pump to offset the friction losses of water moving through a pipe.

friction layer Earth Science. the thin layer of the atmosphere adjacent to the earth’s surface.

Fritts, Charles U.S. inventor who built the first genuine solar cell (1883), using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold. His devices were not efficient, but they proved the viability of light as an energy source.

front-wheel drive Transportation. describing a vehicle in which only the front wheels receive driving power from the engine (as opposed to the traditional rear-wheel drive).

Fruehauf, August 1868–1930, U.S. carriage builder who invented the tractor trailer, a truck with the cab and engine separate from the main cargo-carrying body of the truck.

FTA 1. Federal Transit Administration. 2. fault tree analysis.

fuel Materials. 1. any material that evolves energy in a chemical or nuclear reaction. 2. specifically, a material that can be used to provide power for an engine, combustor, power plant, nuclear reactor, and so on.

fuel assembly see FUEL ELEMENT.

fuel-borne catalyst (FBC) Materials. a chemical compound of an organic and a metal added to a fuel to make a metal ash that promotes the combustion of soot collected with it in a diesel particulate filter (DPF).

fuel cell Renewable/Alternative. a device that converts the chemical energy of a fuel directly into electricity and heat without combustion, through a process of oxidation; fuel cells differ from conventional electrical cells in that the active materials, such as hydrogen and oxygen, are not contained within the cell, but are supplied from outside. RSee next page.

fuel-cell furnace Conversion. a dual-chamber furnace in which partial combustion takes place in a primary chamber and combustion is then completed in the secondary chamber.

fuel cell poisoning Renewable/Alternative. a term for the degradation of a fuel cell’s performance because of impurities in the fuel binding to the catalyst.

fuel cell stack Renewable/Alternative. an array of individual fuel cells connected in series, for the purpose of increasing electrical current.

fuel cell vehicle Renewable/Alternative. an electric-drive vehicle that derives the power for its drive motor(s) from a fuel cell system; a hybrid fuel cell vehicle also derives drive motor power from a supplemental battery or ultracapacitor.

fuel cladding see CLADDING.

fuel crisis see ENERGY CRISIS.

fuel cycle Consumption & Efficiency. the total life of a given fuel in all of its uses and forms, including its extraction or generation, transportation, combustion, air emission, byproduct removal, and waste transportation and disposal.

fuel cycle analysis Environment. 1. an evaluation of environmental impact that considers the effects of obtaining a fuel (e.g., mining coal or harvesting wood), as well as the more commonly assessed impacts of burning the fuels for useful heat or electricity. 2. another


fuel economy


fuel temperature coefficient

Rfuel cell Fuel cells have been known for 150 years. William Grove, British physicist and a justice of Britain’s high court, first

constructed a “wet-cell” battery in 1838. Grove constructed one of the first fuel cells by immersing two platinum electrodes in a container of sulfuric acid. When the two electrodes are separately sealed in chambers containing oxygen and hydrogen, a constant current would flow between the electrodes. The chemical energy of the fuel oxidation is directly converted to electricity with no intermediate mechanical moving parts. Due to the direct nature of energy conversion, fuel cells are not limited by Carnot cycle considerations. Since the initial construction by Grove, fuel cells have come a long way and are on the verge of large scale commercial applications. The basic unit of a fuel cell consists of three components: cathode, anode, and electrolyte. Ionic transport of one type of species occurs from one electrode chamber to another through the electrolyte with compensating electrical current in the external

circuit. Typically, the voltage from a single cell is c. 1.0 Volt. Several cells are connected together in a series-parallel arrangement to form the fuel cell stack. Fuel cells can be classified on the basis of the type of electrolyte: proton exchange membrane fuel cells (PEMFCs), solid oxide fuel cells (SOFCs), alkaline fuel cells (AFCs), molten carbonate fuel cells (MCFCs), and phosphoric acid fuel cells (PAFCs). Fuel cell systems are modular, noiseless, and environmentally friendly with reduced emissions of greenhouse gases and no acid rain causing nitrogen and sulfur oxide emissions. Further, SOFCs and MCFCs can be combined with conventional power generation systems in hybrid cycles resulting in power generation efficiencies as high as 60%. In the coming decades they are expected to find applications in residential, transportation and stationary power generation applications.

Srikanth Gopalan

Boston University

fuel economy Transportation. 1. a standard measure of the rate of motor vehicle fuel consumption, expressed as the total distance traveled divided by the amount of gasoline fuel consumed in doing this. 2. a general statement of this based on the average mileage traveled per unit of fuel for a class of vehicles; e.g., a certain car type in a given model year. RSee next page.

fuel efficiency Transportation. the efficiency with which a motor vehicle converts energy into movement. Not necessarily equivalent to FUEL ECONOMY, in that one vehicle might have better technology and thus be more efficient than another, but if it is much larger and heavier than the other vehicle, it would have poorer fuel economy.

fuel element Nuclear. a cluster of fuel pins mounted into a single assembly.

fuel ethanol see ETHANOL.

fuel fabrication Nuclear. the process of making reactor fuel assemblies, usually from sintered uranium oxide pellets that are inserted into zircalloy tubes, comprising the fuel rods or elements.

fuel injection Transportation. a system for delivering fuel directly under pressure into the cylinder or combustion chamber of a

spark–ignition engine, thus eliminating the need for a conventional carburetor; used in diesel engines and in many gasoline engines.

fuel pellet Nuclear. a small cylinder of enriched uranium, typically uranium oxide; several pellets are assembled into a fuel pin, which then forms a component of a fuel element.

fuel pin Nuclear. a long slender tube made of a zirconium alloy and containing fuel pellets; several fuel pins bundled together form a fuel element.

fuel reformer see REFORMER.

fuel rod see FUEL ELEMENT .

fuel share Consumption & Efficiency. the percentage of total fuel use accounted for by an individual fuel; can be measured in dollars or in physical units such as joules.

fuel-switching Consumption & Efficiency. the potential ability of a manufacturer or power generator to use a different energy source in place of that actually consumed, by a substitution within a short time and without extensive modifications.

fuel temperature coefficient Nuclear. the change in reactivity per degree change in nuclear fuel temperature.




Rfuel economy Fuel economy is most often measured by the distance a vehicle can

travel on a given volume of fuel (or the inverse). In the U.S. fuel economy is measured in vehicle miles per gallon of fuel. In the European Union liters per 100 kilometers is the preferred measure. Fuel economy is an imprecise measure of energy efficiency as it does not take into account vehicle mass, passenger or cargo capacity, engine power or other attributes that may affect the value of a vehicle’s services. In addition, different fuels contain varying amounts of energy per volume. For example, diesel fuel contains approximately 11% more energy per volume than gasoline. Devising comparable volume-based fuel economy measures for liquid and gaseous fuels and electricity raises as yet unresolved problems. For these reasons, some prefer alternative measures of energy efficiency, such as ton-kilometers per megajoule. Fuel economy depends not only on the efficiency with which a vehicle's power train converts the energy in fuel into useful work at the wheels, but also on vehicle mass, aerodynamics and rolling resistance, as well as how the vehicle is driven and the ambient conditions under which it is operated. Speed affects fuel economy through the number of engine revolutions required per distance traveled and because

aerodynamic drag increases with the square of velocity. Idling reduces fuel economy because fuel is consumed while the vehicle is not moving. Frequent braking reduces fuel economy by converting the kinetic energy of the vehicle into heat which is then dissipated (regenerative braking allows hybrid vehicles to recapture and store some of this energy in the form of electricity). Cold weather also degrades fuel economy because internal combustion engines are much less efficient before they are fully warmed up and warm up takes longer in cold weather. To permit consistent comparisons among different vehicles, governments and vehicle manufacturers measure passenger car and light truck fuel economy under laboratory conditions over strictly specified driving cycles. A driving cycle is defined by a program of vehicle velocity as a function of time. The U.S., European Union and Japan all use different driving cycles to better approximate typical driving conditions in their regions. The fuel economy individual drivers realize will deviate from these standardized measures depending on the conditions under which they drive and their driving styles.

David L. Greene

Oak Ridge National Laboratory

fuelwood Biomass. firewood; wood and wood products burnt as fuel.

fuelwood crisis Sustainable Development. a severe shortage of wood for heating and cooking purposes, either historic (e.g., England in the Middle Ages) or contemporary (less developed countries in Asia and sub-Saharan Africa).

fugacity Thermodynamics. a function that is introduced as an effective substitute for pressure, to allow a real gas system to be considered by the same equations that apply to an ideal gas.

fugitive air Mining. 1. air that moves through a ventilating fan but that does not reach the active working face, e.g., that is lost through leaks in the ventilating system. 2. any unintended release of air during a mining operation.

fugitive dust Mining. a term for silt, dust, and sand that becomes airborne and is thereby carried away from a mine property by air currents.

fugitive emission(s) Oil & Gas. an unintended leak of gas from the processing, transmission, or transportation of fossil fuels.

full-cost pricing Economics. a price for a good or service that would include the cost of externalities; e.g., a price for electricity from a coalfired power plant that includes the cost of the damage to human health caused by the sulfur dioxide released in coal combustion.

Fuller, R. Buckminster 1895–1983, U.S. inventor, architect, engineer, and mathematician, best known for his invention of the GEODESIC DOME. Fuller was an early proponent of renewable energy sources, which he incorporated into his designs.

fullerene Materials. any of various cagelike molecules that constitute the third form of pure carbon (along with the historically known forms diamond and graphite), whose prototype C60 (the buckyball) is the roundest molecule that exists. Fullerenes are a class of discrete molecules, soccer ball-shaped

full extraction



forms of carbon with extraordinary stability. [Named for Buckminster Fuller; their configuration suggests the shape of his famous geodesic dome.]

full extraction Mining. an underground coal mining technique that removes the coal in large areas, causing the void to be filled in with caved rock.

full pool Hydropower. the elevation of a reservoir at its maximum normal operating level; i.e., at full height but within holding capacity and not spilling over.

full sun Solar. the amount of power density of solar radiation received at the earth’s surface at noon on a clear day (about 1000 W/m2).

Fulton, Robert 1765–1815, U.S. inventor who made steamboating a practical and widespread mode of transportation, with the successful voyage of the Clermont on the Hudson River from New York to Albany in 1807.

fumarole Earth Science. a vent or hole in the earth’s surface, usually in a volcanic region, from which steam, gaseous vapors, or hot gases are released.

fumes Materials. 1. the smoky particulate matter that emanates from heated materials. 2. vapors evolved from concentrated acids or solvents. Fume particles are solid particles of very small size (under 1 micron in diameter) formed as such vapors condense, or as chemical reactions take place.

Fumifugium History. the title of a paper published by Englishman John Evelyn in 1661 (“Fumifugium, or the Inconvenience of the Aer and Smoake of London Dissipated”), one of the earliest tracts on air pollution. Evelyn described the poor air quality of London and suggested remedies to deal with this, such as relocating energy-intensive industries (ironmaking, brewing) outside the city, and planting gardens and orchards in their place.

fundamental particle see ELEMENTARY PAR-


fund pollutant Environment. a term for a pollutant substance that can be naturally absorbed by the environment at least to some extent, as opposed to a substance that will remain indefinitely if not actively removed (stock pollutant). However, a fund pollutant will accumulate if its rate of emission exceeds the capacity of the environment to absorb it.

Fundy, Bay of Renewable/Alternative. a body of water off the coastline of Nova Scotia, Canada; highly suited to use for tidal power because it has the largest tidal changes in the world (a difference between high and low tides of as much as 50 ft).

furl Wind. 1. to roll up and fasten a sail so that it will not capture the wind. 2. to point the blades of a wind turbine out of the wind.

furling speed Wind. the amount of wind required to produce the maximum power that a wind energy device is capable of generating; any wind in excess of that speed will not generate more than this maximum.

furling tail Wind. a protection mechanism in a wind energy device that allows the tail of the device to fold up and in during unsuitably high winds; this causes the blades to turn out of the wind, protecting the machine.

furnace HVAC. an enclosed structure in which heat energy is produced to warm a building space, heat a substance of interest, or create some other physical or chemical effect.

furnace A contemporary blast furnace used for steelmaking; its temperatures can reach 1650°C (3000°F).

fuse Electricity. 1. a protective device based on a wire or element that melts at low temperature; when the current through the fuse exceeds the fuse rating, the wire melts and opens the circuit. 2. Materials. a combustible substance enclosed in a continuous cord, used for initiating an explosive charge by transmitting fire to it.

fusion Chemistry. 1. the process of melting; the conversion of a solid into a liquid by

fusion reactor


fuzzy logic

means of heat or pressure. 2. Nuclear. a nuclear process in which two light nuclei combine at extremely high temperatures to form a heavier nucleus and release vast amounts of energy. The explosive force of a hydrogen bomb is an example of uncontrolled fusion, and the energy of the sun and other stars is believed to derive from fusion reactions.

fusion reactor Nuclear. a nuclear reactor that produces energy by fusing light nuclei together, instead of splitting heavy nuclei apart as in the fission process.

fusion triple product Nuclear. the three quantities that together define the energy-break- even point for fusion reactions. The rate of fusion in the fuel, f, is constant for any given amount of fuel in a particular state; the actual net energy released is a function of f (and in turn, the temperature T), the number of particles in a particular area (its density N), and the amount of time they remain together (the confinement time t). The fusion triple product

ntT must be above a certain value for a successful confinement scheme.

futures (contract) Economics. an agreement between a buyer and a seller for purchase or sale of a given quantity of an asset, such as electricity or oil, at a certain time in the future for a certain price; this may or may not result in an actual physical exchange of the asset. Futures often are traded in a futures market (e.g., the New York Mercantile Exchange), in which they are used to transfer risk and to generate gains through speculation or arbi-

trage. Compare FORWARD CONTRACT.

fuzzy logic Communication. 1. problemsolving that involves a certain degree of inference and intuition to reach the proper conclusion; regarded as a crucial distinction between human intelligence and machine reasoning. 2. a level of artificial intelligence that can process uncertain or incomplete information; characteristic of many expert systems.


G Measurement. 1. a unit of acceleration equal to the standard acceleration of gravity, or about 9.8 meters per second per second.

2.an abbreviation for gravity or gravitation.

3.short for giga- (one billion).

G-7 a group of seven major industrialized countries whose heads of state meet to discuss economic and political issues; the U.S., Canada, Japan, Britain, France, Germany, and Italy. Also known as G-8 with inclusion of Russia.

G-77 a coalition of developing countries, intended to promote the collective economic interests of its members and enhance their negotiating capacity. Originally with 77 members (1964), it now has more than 130.

Gadget Nuclear. the code name given to the first nuclear device tested by the U.S. (July 16, 1945) in its efforts to develop an atomic bomb for use as a weapon in World War II.

Gaia hypothesis Earth Science. the proposal that the earth can be conceived of a single living super-organism, and that the presence of life on earth has played a fundamental role in establishing the physical and chemical conditions that now exist on the planet. [Named for the ancient Greek goddess of the earth.]

gain Electricity. 1. the increase in signal power produced by an amplifier. 2. see HEAT GAIN.

Galilean History. relating to Galileo or to his theories and discoveries.

Galilean relativity Physics. a concept based on Galileo’s investigations into the performance of falling bodies, reportedly based on an experiment in which he dropped two different weights from the top of the Leaning Tower of Pisa. It states that the acceleration of a given particle will have the same value in all frames of reference that are moving at constant velocity in relation to each other. (This

applies at ordinary speeds but not at speeds approaching the speed of light.)

Galileo Galilei 1564–1642, Italian astronomer and physicist associated with many of the important advances in science in the late Middle Ages. He made major investigations in mechanics, including experiments on acceleration, friction, inertia, and falling bodies. He improved the telescope and pioneered its use for astronomical observation, discovering mountains on the moon, many new stars, the four satellites of Jupiter, and the composition of the Milky Way. He also supported the theories of Copernicus concerning the motion of the planets.

gallium Chemistry. a rare metallic element having the symbol Ga, the atomic number 31, an atomic weight of 69.72, a melting point of 29.78°C, and a boiling point of 2403°C; a sil- ver-white metal used for doping semiconductors and producing solar cells and solid-state devices such as transistors.

gallium arsenide Materials. GaAs, dark gray crystals that are electroluminescent in infrared light; a semiconductor material formed by combining gallium and arsenic, used in transistors, solar cells, and semiconducting lasers.

gallon Measurement. a traditional unit of volume made up of 4 quarts; the U.S. unit for gasoline and various other liquids. The U.S. standard gallon is 128 fluid ounces or 231 cubic inches; equivalent to 3.785 liters. The British imperial gallon is 160 fluid ounces or 277.4 cubic inches; equivalent to 4.546 liters.

Galvani, Luigi 1737–1798, Italian anatomist who discovered the relationship between electricity and animation (1771), while dissecting a frog. He touched an exposed nerve of the frog with his metal scalpel, and he observed the dead frog’s leg kick as if in life. He had discovered the electrical nature of the nerve–muscle function, thus establishing the basis for the study of neurophysiology.

galvanic Electricity. describing a flow of electricity that results from chemical activity.

galvanic cell Electricity. a device that generates an electrical current, consisting of dissimilar metals in contact with each other and with an electrolyte. A galvanic battery is composed of one or more such cells.

galvanic corrosion


gas hydrate

galvanic corrosion Materials. the corrosion of a metal caused or accelerated by an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte.

galvanic series Materials. a listing of metals according to their potential or ease of oxidation in a given environment, with lithium at the negative (least noble) end and platinum at the positive (most noble) end.

galvanism History. an earlier term for the production of electricity by chemical action; so called because this was studied by Galvani.

galvanometer Measurement. an instrument that measures a small electric current by measuring the mechanical motion derived from electromagnetic or electrodynamic forces produced by the current.

game theory Economics. a tool for evaluating optimal behavior strategies, often in economics, that is based on a theory of making the best choice from among available strategies given imperfect information.

gamma Measurement. a unit of measure for the strength of a magnetic field, equivalent to 0.00001 (10–5) oersted.

gas Chemistry. 1. one of the three fundamental forms of matter, along with liquids and solids. Unlike a solid (and like a liquid), a gas has no fixed shape and will conform in shape to the space available. Unlike a liquid, it has no fixed volume and will conform in volume to the space available. In comparison with solids and liquids, gases have widely separated molecules, are light in weight, and are easily compressed. 2. short for GASOLINE.

gas bubble trauma Environment. a fatal or sublethal fish syndrome that occurs when gas in supersaturated water comes out of solution and reaches chemical equilibrium with atmospheric conditions, leading to the formation of bubbles within the tissue of aquatic organisms.

gas cap Oil & Gas. a term for the gas that accumulates in the upper portions of a reservoir where the pressure, temperature, and fluid characteristics are conducive to free gas.

gas centrifuge Nuclear. a system for the enrichment of uranium, in which uranium hexafluoride gas is spun in a centrifuge fast enough for the heavier isotope of uranium to be partially separated from the lighter one.

gas chromatography Chemistry. a process in which a gas mixture is passed through a cylinder and the different chemicals that make up the gas adhere to the surface of the cylinder at different intervals. This information is then used to determine the chemical makeup of the gas.

gas condensate see CONDENSATE.

gas-cooled fast reactor (GFR) Nuclear. an advanced nuclear reactor design in the development stage featuring a fast-neutron spectrum, helium-cooled reactor and a closed fuel cycle. The high outlet temperature (850°C) of the helium coolant makes it possible to deliver electricity, hydrogen, or process heat with high efficiency.

gas-cooled graphite-moderated reactor

Nuclear. a type of graphite-moderated nuclear reactor distinguished by its use of a gas, usually carbon dioxide or helium, as a coolant, and its ability to use natural uranium as well as enriched uranium as a fuel.

gas drive Oil & Gas. a primary recovery mechanism for oil wells containing dissolved and free gas, in which the energy of the expanding gas is used to propel the oil from the reservoir into the wellbore.

gaseous Materials. existing as a gas; having the characteristics of a gas rather than a liquid or solid.

gas fill HVAC. an inert gas such as argon, used instead of air in a sealed space for greater insulation value; e.g., between dual windowpanes.

gas guzzler Transportation. a motor vehicle that has a poor fuel consumption performance; currently defined in the U.S. as a fuel economy of less than 22.5 miles per gallon. A gas-guzzler tax is a federal tax collected on the original manufacturer’s sale of an automobile with fuel economy below this level (or another prescribed level).

gas hydrate Materials. a solid, crystalline, wax-like substance composed of water, methane, and usually a small amount of other gases, with the gases being trapped in the interstices of a water and ice lattice. Gas hydrates form beneath the permafrost and on the ocean floor under conditions of moderately high pressure and at temperatures near the freezing point of water. Gas hydrates have



Gassner, Carl

gas guzzler The term “gas guzzler” was coined at the time when most Americans first became aware of the issue of fuel consumption, during the energy crisis of 1973–74. It describes large vehicles such as these, the U.S. norm at the time.

been proposed as a possible future source of natural gas.

gasification Conversion. a thermochemical process that converts a solid or liquid fuel source (e.g., coal) to a gaseous fuel.

gasifier Conversion. any of various devices employed for the production of gas, such as a unit to produce synthesis gas from coal, or to produce gaseous fuel from solid or liquid biomass (e.g., agricultural wastes).

gaslight History. illumination by coal gas; the dominant form of urban lighting prior to the development of electric light. Thus, gaslamp.

gasohol Oil & Gas. gasoline and alcohol; a mixture typically containing about 90% unleaded gasoline and 10% ethyl alcohol; used as an alternative fuel in some automobile and truck engines.

gas oil or gasoil Oil & Gas. a liquid petroleum distillate having a viscosity intermediate between that of kerosene and lubricating oil. It derives its name from its original use in the manufacture of illuminating gas. It is now used for diesel fuel, heating fuel, and also as a feedstock.

gas–oil ratio Oil & Gas. the number of cubic feet of natural gas produced with a barrel of oil; an approximation of the composition

of oil and gas from a reservoir, expressed in cubic feet of gas per barrel of oil at standard temperature and pressure.

gasoline Oil & Gas. a volatile liquid mixture of hydrocarbons that is obtained by refining petroleum and that is used as the fuel in most internal-combustion engines.

gasoline additive see ADDITIVE.

gasoline blending Oil & Gas. the technique of mixing up to 15 different hydrocarbon streams to produce a gasoline with specific characteristics, including vapor pressure, boiling points, sulfur content, color, stability, aromatics content, olefin content, octane rating, and also other governmental or market restrictions.

gasoline equivalent gallon Measurement. the volume of natural gas that equals the energy content of one gallon of gasoline, in order to compare equivalent volumes of the two fuels based on their energy content in Btu (since natural gas is normally measured in cubic feet).

gasoline grade Oil & Gas. the classification of gasoline by octane ratings; see REGULAR;


gasometer Measurement. an apparatus used to contain and measure gas, particularly for chemical studies. Thus, gasometry, gasometric.

gas shale Oil & Gas. natural gas stored within an organically rich shale interval (reservoir), and requiring natural fractures and artificial well stimulation for acceptable rates of gas flow to take place.

gas shift process Chemistry. a process in which carbon monoxide and hydrogen react in the presence of a catalyst to form methane and water.

gassing Storage. 1. the evolution of gas from one or more electrodes in the cells of a battery; this commonly results from local selfdischarge or from the electrolysis of water in the electrolyte during charging. 2. any evolution of gases during an event.

gassing current Electricity. the portion of charge current that goes into electrolytic production of hydrogen and oxygen from an electrolytic liquid; this current increases with increasing voltage and temperature.

Gassner, Carl 1839–1882, German scientist who invented the first dry cell battery (1888).

gas supersaturation


Geissler tube

He used zinc as the container for the other elements and for the negative electrode. The electrolyte was absorbed in a porous material and the cell was sealed across the top. This led to the modern carbon–zinc battery.

gas supersaturation Environment. the overabundance of gases in turbulent water, as at the base of a dam spillway, that can cause a fatal condition in fish known as GAS BUBBLE


gassy Mining. describing a situation in which a mine gives off methane or other gas in quantities that must be diluted with pure air to prevent an occurrence of explosive mixtures.

gas thermometer Measurement. a thermometer that utilizes the thermal properties of gas (as opposed to one that uses a liquid such as mercury), either by maintaining the gas at constant volume and observing changes in pressure, or vice versa.

gas-to-liquid (GTL) Oil & Gas. a process that combines the carbon and hydrogen elements in natural gas molecules to make synthetic liquid petroleum products, such as diesel fuel.

gas-to-oil ratio see GASOIL RATIO.

gas turbine Conversion. a rotary engine in which liquid or gaseous fuel is burned to produce electric power and heat. Hot combustion gases are passed to the turbine, where they expand to drive a generator and are then used to run a compressor.

gas-turbine engine Transportation. a type of internal combustion engine in which the shaft is spun by the pressure of combustion gases flowing against curved turbine blades located around the shaft.

gasworks Coal. a facility where coal gas is produced for use in lighting and heating.

GATT Policy. General Agreement on Tariffs and Trade; a multilateral trade agreement signed in 1948 among autonomous economic entities (not necessarily countries), aimed at expanding international trade as a means of raising global welfare. GATT was superseded by the World Trade Organization (WTO) in 1995.

Gauss, Karl Friedrich 1777–1855, German mathematician who proved fundamental theorems of algebra and arithmetic and made major contributions in areas such as geometry, number theory, and probability.

gauss Measurement. a unit of magnetic induction in the centimeter-gram-second system, equivalent to 1 maxwell per cm2.

Gauss law Electricity. a description of the relation between the electric flux flowing out from a closed surface and the charge enclosed in the surface; the amount of charge within the surface is proportional to the flux.

Gauss principle Physics. the principle that a system of interconnected particles, subjected to a certain set of forces, will have nearly the same motion that the particles would have if disconnected from each other but still subjected to the same forces; i.e., the constraints on the overall system are minimal.

Gay-Lussac, Joseph Louis 1778–1850, French chemist noted for his original investigations into the behavior of gases. He deduced that gases at constant temperature and pressure combine in very simple numerical proportions by volume.

GCM general circulation model. GDP gross domestic product.

Gedser turbine Wind. a 200 kW wind turbine built in 1957 on the Gedser coast of southern Denmark, considered to be the first wind turbine connected with an (asynchronous) AC generator to an electrical grid. It had huge 24 meter sails and was for many years the largest wind turbine in the world. It operated for 11 years with little maintenance and is now displayed at the Danish Museum of Electricity.

GEF Global Environment Facility.

Geiger counter Nuclear. a device that detects the passage of charged particles by means of the ionization of gas that they cause as they pass through a region; used to detect the particles produced in certain forms of radioactivity. [Invented by German physicist Hans Geiger, 1882–1947.]

Geissler (mercury) pump Lighting. a glass water pump in which a vacuum is created when mercury flows between two reservoirs, one of which is fixed and the other variable; this technology contributed to the success of Edison’s first incandescent lamps, being used to remove air from the lightbulb. [Developed by German physicist Johann Heinrich Wilhelm Geissler, 1814–1879.]

Geissler tube Electricity. a gas-filled, dualelectrode discharge tube that emits brilliant

Gell-Mann, Murray


general gas law

and colorful fluorescent light when high voltage is passed through it, a demonstration of the luminous effects of discharges through rarefied gases. The Geissler tube led to the discovery of electrons.

Gell-Mann, Murray born 1929, U.S. physicist noted for his classification of subatomic particles and their interactions. In 1961 he and Israeli physicist Yuval Ne’eman independently proposed a scheme for classifying strongly interacting particles into a simple, orderly arrangement of families based on common general characteristics.

gel-type battery Storage. a lead-acid battery in which the electrolyte is immobilized in a gel; usually used for mobile installations in situations in which the battery will be subject to high levels of shock or vibration.

GEM lamp Lighting. General Electric Metallized lamp; an improved type of incandescent lamp employing a metal-like carbon filament, introduced in 1904. It provided greater energy efficiency than earlier carbon lamps.

General Agreement on Tariffs and Trade see


general aviation Transportation. a term for all facets of civil aviation except commercial air carriers.

general circulation Earth Science. the complete range of large-scale motions of the atmosphere and the ocean as a result of differential heating on a rotating earth, acting to restore the energy balance of the system through the transport of heat and momentum.

general circulation model (GCM) Earth Science. a computerized model of the dynamics and energetics of atmospheric circulation on a global scale, used to understand historic changes in climate, and to predict future changes due to forces such as the emission of greenhouse gases from human energy use. RSee below.

General Electric Company (GE) a large multinational energy corporation founded by Thomas Alva Edison in 1892 that originally was in the business of generating and selling electricity; it now works in many other areas of the energy industry.

general equilibrium model Economics. an approach that simultaneously considers all markets in an economy, allowing for feedback effects between individual markets. It is particularly concerned with the conditions that permit simultaneous equilibrium in all markets and with the properties of such an equilibrium. Also, general equilibrium analysis.

general gas law another term for the IDEAL


Rgeneral circulation models General circulation models (GCMs) are computer

models of the climate system used to quantify climate response to a change in radiative forcing. The models describe the major components of the climate system such as the atmosphere, oceans, terrestrial biosphere, glaciers and ice sheets, and land surface. In order to project the impact of human perturbations on the climate system, GCMs represent the key processes operating in the climate system and the complex interactions and feedbacks among these components. These climate processes are represented in mathematical terms based on physical laws such as the conservation of mass, momentum, and energy. The complexity of the climate system means that the calculations from these mathematical equations can be performed in practice only by using a powerful computer. The equations are solved numerically at a finite resolution using a three-dimensional grid over the globe. Typical resolutions used for

simulations are about 250 km in the horizontal and 1 km in the vertical. Many physical processes cannot be properly resolved at such coarse spatial resolutions and one resorts to including their average effect through parametric representations. GCMs form the basis for forecasting future climate change and its possible impacts by calculating how future emissions of greenhouse gases lead to changes into their atmospheric concentrations, how changes in concentration produce changes in global radiative forcing, how that radiative forcing in turn changes global mean temperature, and finally, how changes in temperature generate environmental changes such as global mean sea level rise. A future research challenge is to include chemistry, biology and ecology into the climate system models to improve the representation of the various processes and feedbacks in the system.

Ranga Myneni

Boston University