In thermodynamics , a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work .
The working substance generates work in the " working body " of the engine while transferring heat to the colder " sink " until it reaches a low temperature state.
Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem . Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can be easily converted to heat by processes like exothermic reactions , absorption of light or energetic particles, friction , dissipation and resistance .
Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines are very versatile and have a wide range of applicability.
Since very few actual implementations of heat engines exactly match their underlying thermodynamic cycles, one could say that a thermodynamic cycle is an ideal case of a mechanical engine.
On Earth, the cold
side of any heat engine is limited to being close to the ambient
temperature of the environment, or not much lower than 300 Kelvin , so
most efforts to improve the thermodynamic efficiencies of various heat
engines focus on increasing the temperature of the source, within
material limits.
The maximum theoretical efficiency of a heat engine is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, all expressed in absolute temperature or kelvins .
The efficiency of various heat engines proposed or used today ranges from 3 percent for the OTEC ocean power proposal through 25 percent for most automotive engines, to 45 percent for a supercritical coal-fired power station , to about 60 percent for a steam-cooled combined cycle gas turbine .
Examples of everyday heat engines include the steam engine , the diesel engine , and the gasoline engine in an automobile .
A common toy that is also a heat engine is a drinking bird . Also the stirling engine is a heat engine.
For example, John Ericsson developed an external heated engine running on a cycle very much like the earlier Diesel cycle . In addition, externally heated engines can often be implemented in open or closed cycles.
Mesoscopic heat engines are nanoscale devices that may serve the goal of processing heat fluxes and perform useful work at small scales.
There is exact equality that relates average of exponents of work performed by any heat engine and the heat transfer from the hotter heat bath. This relation transforms the Carnot's inequality into exact equality.
The efficiency of a heat engine relates how much useful work is output for a given amount of heat energy input. is positive.) is the heat energy delivered to the cold temperature system. (It is positive since heat is added to the sink.)
In other words, a heat engine absorbs heat energy from the high temperature heat source, converting part of it to useful work and delivering the rest to the cold temperature heat sink.
The theoretical maximum efficiency of any heat engine depends only on the temperatures it operates between. This efficiency is usually derived using an ideal imaginary heat engine such as the Carnot heat engine , although other engines using different cycles can also attain maximum efficiency.
It is first assumed that if a more efficient heat engine than a Carnot engine is possible, then it could be driven in reverse as a heat pump.
Empirically, no heat engine has ever been shown to run at a greater efficiency than a Carnot cycle heat engine.
The working substance generates work in the " working body " of the engine while transferring heat to the colder " sink " until it reaches a low temperature state.
Heat engines distinguish themselves from other types of engines by the fact that their efficiency is fundamentally limited by Carnot's theorem . Although this efficiency limitation can be a drawback, an advantage of heat engines is that most forms of energy can be easily converted to heat by processes like exothermic reactions , absorption of light or energetic particles, friction , dissipation and resistance .
Since the heat source that supplies thermal energy to the engine can thus be powered by virtually any kind of energy, heat engines are very versatile and have a wide range of applicability.
Since very few actual implementations of heat engines exactly match their underlying thermodynamic cycles, one could say that a thermodynamic cycle is an ideal case of a mechanical engine.
The maximum theoretical efficiency of a heat engine is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, all expressed in absolute temperature or kelvins .
The efficiency of various heat engines proposed or used today ranges from 3 percent for the OTEC ocean power proposal through 25 percent for most automotive engines, to 45 percent for a supercritical coal-fired power station , to about 60 percent for a steam-cooled combined cycle gas turbine .
Examples of everyday heat engines include the steam engine , the diesel engine , and the gasoline engine in an automobile .
A common toy that is also a heat engine is a drinking bird . Also the stirling engine is a heat engine.
For example, John Ericsson developed an external heated engine running on a cycle very much like the earlier Diesel cycle . In addition, externally heated engines can often be implemented in open or closed cycles.
Mesoscopic heat engines are nanoscale devices that may serve the goal of processing heat fluxes and perform useful work at small scales.
There is exact equality that relates average of exponents of work performed by any heat engine and the heat transfer from the hotter heat bath. This relation transforms the Carnot's inequality into exact equality.
The efficiency of a heat engine relates how much useful work is output for a given amount of heat energy input. is positive.) is the heat energy delivered to the cold temperature system. (It is positive since heat is added to the sink.)
In other words, a heat engine absorbs heat energy from the high temperature heat source, converting part of it to useful work and delivering the rest to the cold temperature heat sink.
The theoretical maximum efficiency of any heat engine depends only on the temperatures it operates between. This efficiency is usually derived using an ideal imaginary heat engine such as the Carnot heat engine , although other engines using different cycles can also attain maximum efficiency.
It is first assumed that if a more efficient heat engine than a Carnot engine is possible, then it could be driven in reverse as a heat pump.
Empirically, no heat engine has ever been shown to run at a greater efficiency than a Carnot cycle heat engine.
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