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In thermodynamics, the thermal efficiency () is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a steam turbine or a steam engine, a boiler, a furnace, or a refrigerator for example. For a power cycle, thermal efficiency indicates the extent to which the energy added by heat is converted to net work output. In the case of a refrigeration or heat pump cycle, thermal efficiency indicates the extent to which the energy added by work is converted to net heat output. ==Overview== In general, energy conversion efficiency is the ratio between the useful output of a device and the input, in energy terms. For thermal efficiency, the input, , to the device is heat, or the heat-content of a fuel that is consumed. The desired output is mechanical work, , or heat, , or possibly both. Because the input heat normally has a real financial cost, a memorable, generic definition of thermal efficiency is〔''Fundamentals of Engineering Thermodynamics'', by Howell and Buckius, McGraw-Hill, New York, 1987〕 : From the first law of thermodynamics, the energy output cannot exceed the input, so : When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Efficiency is typically less than 100% because there are inefficiencies such as friction and heat loss that convert the energy into alternative forms. For example, a typical gasoline automobile engine operates at around 25% efficiency, and a large coal-fueled electrical generating plant peaks at about 46%. The largest diesel engine in the world peaks at 51.7%. In a combined cycle plant, thermal efficiencies are approaching 60%.〔(GE Power’s H Series Turbine )〕 Such a real-world value may be used as a figure of merit for the device. For engines where a fuel is burned there are two types of thermal efficiency: indicated thermal efficiency and brake thermal efficiency.〔The Internal Combustion Engine in Theory and Practice: Vol. 1 - 2nd Edition, Revised, MIT Press, 1985, Charles Fayette Taylor - Equation 1-4, page 9〕 This efficiency is only appropriate when comparing similar types or similar devices. For other systems the specifics of the calculations of efficiency vary but the non dimensional input is still the same. Efficiency = Output energy / input energy 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「thermal efficiency」の詳細全文を読む スポンサード リンク
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