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| Head |
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The height of a column or body of fluid above a given point expressed in linear units. Head is often used to indicate gage pressure. Pressure is equal to the height times the density of the fluid.
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| Heat |
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The form of energy that has the capacity to create warmth or to increase the temperature of a substance. Any energy that is wasted or used to overcome friction is converted to heat. Heat is measured in calories or British thermal units (Btu's). One Btu is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
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| Heat exchanger |
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A device which transfers heat through a conducting wall from one fluid to another.
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| Heat rate |
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The amount of fuel energy required by a power plant to produce one kilowatt-hour of electrical output.
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| Heating value |
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The maximum amount of energy that is available from burning a substance.
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| Hectare (ha) |
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A metric unit of area, 100 metres by 100 metres (10,000 square metres); equivalent to 2.471 acres.
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| Helical |
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Spiral-shaped: in the shape of a helix or spiral.
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| Hemicellulose |
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A celluloselike material (in wood) that is easily decomposable as by dilute acid, yielding several different simple sugars.
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| Herbaceous |
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Non-woody type of vegetation, usually lacking permanent strong stems, such as grasses, cereals and canola (rape).
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| Herbaceous Energy Crops |
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Perennial non-woody crops that are harvested annually, though they may take 2 to 3 years to reach full productivity. Examples include: Switchgrass, Reed canarygrass, Miscanthus, and Giant reed.
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| Hertz (Hz) |
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Unit of frequency; equal to one cycle per second (cps).
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| Higher heating value (HHV) |
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The maximum potential energy in dry fuel. For wood, the range is from 7,600 to 9,600 Btu/lb (17.7 to 22.3 GJ/t).
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| Hog fuel |
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Waste wood that is used for generation of heat and process energy; made by reducing bark to a usable size.
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| Holocellulose |
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The total carbohydrate fraction of wood –that is, cellulose plus hemicellulose.
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| Horsepower (hp) |
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The power required to lift 550 pounds one foot in one second or 33,000 pounds one foot in one minute. A horsepower is equal to 746 watts or to 42.2 British thermal units per minute.
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| Hydraulic |
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To move or convey by fluid.
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| Hydraulic balance |
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A condition of equal opposed hydraulic forces acting on a part in a hydraulic component.
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| Hydraulic control |
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A control which is actuated by hydraulically induced forces.
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| Hydraulics |
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Engineering science pertaining to liquid pressure and flow.
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| Hydrodynamics |
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Engineering science pertaining to the energy of liquid flow and pressure.
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| Hydrolysis |
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A chemical reaction that releases sugars, which are normally linked together in complex chains. In ethanol production, hydrolysis reactions are used to break down the cellulose and hemicellulose in the biomass.
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| Hydrostatics |
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Engineering science pertaining to the energy of liquids at rest.
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| Hygrometer |
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An instrument for measuring the humidity of air.
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| Hygroscopic |
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Changes its moisture content to be in equilibrium with the atmosphere.
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