Editing Heat engine (section)

== Examples ==
Although some cycles have a typical combustion location (internal or external), they can often be implemented with the other. For example, [[John Ericsson]]<ref name="hae-ericsson1833">{{cite web|url=http://hotairengines.org/closed-cycle-engine/ericsson-1833|title=Ericsson's 1833 caloric engine|work=hotairengines.org}}</ref> 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. In a closed cycle the working fluid is retained within the engine at the completion of the cycle whereas is an open cycle the working fluid is either exchanged with the environment together with the products of combustion in the case of the internal combustion engine or simply vented to the environment in the case of external combustion engines like [[steam engine]]s and [[Steam turbine|turbines]].

=== Everyday examples ===
Everyday examples of heat engines include the [[thermal power station]], [[internal combustion engine]], [[firearm]]s, [[refrigerator]]s and [[heat pump]]s. Power stations are examples of heat engines run in a forward direction in which heat flows from a hot reservoir and flows into a cool reservoir to produce work as the desired product. Refrigerators, [[air conditioner]]s and heat pumps are examples of heat engines that are run in reverse, i.e. they use work to take heat energy at a low temperature and raise its temperature in a more efficient way than the simple conversion of work into heat (either through friction or electrical resistance). Refrigerators remove heat from within a thermally sealed chamber at low temperature and vent waste heat at a higher temperature to the environment and heat pumps take heat from the low temperature environment and 'vent' it into a thermally sealed chamber (a house) at higher temperature.

In general heat engines exploit the thermal properties associated with the expansion and compression of gases according to the [[gas laws]] or the properties associated with [[phase transition|phase changes]] between gas and liquid states.

=== Earth's heat engine ===
Earth's [[atmosphere]] and [[hydrosphere]]—Earth's heat engine—are coupled processes that constantly even out solar heating imbalances through evaporation of surface water, convection, rainfall, winds and ocean circulation, when distributing heat around the globe.<ref name="Lindsey 2009">{{cite journal
|last=Lindsey
|first=Rebecca
|year=2009
|title=Climate and Earth's Energy Budget
|journal=NASA Earth Observatory
|url=http://earthobservatory.nasa.gov/Features/EnergyBalance/
}}</ref>

A [[Hadley cell]] is an example of a heat engine. It involves the rising of warm and moist air in the earth's equatorial region and the descent of colder air in the subtropics creating a thermally driven direct circulation, with consequent net production of kinetic energy.<ref>{{cite journal |author=Junling Huang and Michael B. McElroy|title=Contributions of the Hadley and Ferrel Circulations to the Energetics of the Atmosphere over the Past 32 Years|journal=Journal of Climate |issue=7 |volume=27 |pages=2656–2666 |year=2014 |doi=10.1175/jcli-d-13-00538.1|bibcode=2014JCli...27.2656H|s2cid=131132431 |doi-access=free }}</ref>

=== Phase-change cycles ===
In [[phase transition|phase change]] cycles and engines, the [[working fluid]]s are gases and liquids. The engine converts the working fluid from a gas to a liquid, from liquid to gas, or both, generating work from the fluid expansion or compression.
*[[Rankine cycle]] (classical [[steam engine]])
*[[Regenerative cycle]] ([[steam engine]] more efficient than [[Rankine cycle]])
*[[Organic Rankine cycle]] (Coolant changing phase in temperature ranges of ice and hot liquid water)
*Vapor to liquid cycle ([[drinking bird]], [[injector]], [[Minto wheel]])
*Liquid to solid cycle ([[frost heaving]] – water changing from ice to liquid and back again can lift rock up to 60&nbsp;cm.)
*Solid to gas cycle ([[firearm]]s  – solid propellants combust to hot gases.)

=== Gas-only cycles ===
In these cycles and engines the working fluid is always a gas (i.e., there is no phase change):
*[[Carnot cycle]] ([[Carnot heat engine]])
*[[Ericsson cycle]] (Caloric Ship John Ericsson)
*[[Stirling cycle]] ([[Stirling engine]],<ref name="hae-stirling1842">{{cite web|url=http://hotairengines.org/closed-cycle-engine/stirling-1827/stirling-dundee-engine|title=Stirling's Dundee engine of 1841|work=hotairengines.org}}</ref> [[thermoacoustic refrigeration|thermoacoustic]] devices)
*[[Internal combustion engine]] (ICE):
**[[Otto cycle]] (e.g. [[petrol engine|gasoline/petrol engine]])
**[[Diesel cycle]] (e.g. [[Diesel engine]])
**[[Atkinson cycle]] (Atkinson engine)
**[[Brayton cycle]] or [[Joule cycle]] originally [[Ericsson cycle]] ([[gas turbine]])
**[[Lenoir cycle]] (e.g., [[pulse jet engine]])
**[[Miller cycle]] (Miller engine)

=== Liquid-only cycles ===
In these cycles and engines the working fluid are always like liquid:
*[[Stirling cycle]] ([[Malone engine]])

=== Electron cycles ===
*[[Johnson thermoelectric energy converter]]
*Thermoelectric ([[Peltier–Seebeck effect]])
*[[Thermogalvanic cell]]
*[[Thermionic emission]]
*[[Thermotunnel cooling]]

=== Magnetic cycles ===
*[[Thermo-magnetic motor]] (Tesla)

=== Cycles used for refrigeration ===
{{Main|Refrigeration}}
A domestic [[refrigerator]] is an example of a [[heat pump]]: a heat engine in reverse. Work is used to create a heat differential. Many cycles can run in reverse to move heat from the cold side to the hot side, making the cold side cooler and the hot side hotter. Internal combustion engine versions of these cycles are, by their nature, not reversible.

Refrigeration cycles include:
*[[Air cycle machine]]
*[[Gas-absorption refrigerator]]
*[[Magnetic refrigeration]]
*[[Stirling engine#Stirling cryocoolers|Stirling cryocooler]]
*[[Vapor-compression refrigeration]]
*[[Vuilleumier cycle]]

=== Evaporative heat engines ===
The Barton evaporation engine is a heat engine based on a cycle producing power and cooled moist air from the evaporation of water into hot dry air.

=== Mesoscopic heat engines ===
Mesoscopic heat engines are nanoscale devices that may serve the goal of processing heat fluxes and perform useful work at small scales. Potential applications include e.g. electric cooling devices. In such mesoscopic heat engines, work per cycle of operation fluctuates due to thermal noise. 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.<ref name='sinitsyn-11jpa'>{{cite journal|title=Fluctuation Relation for Heat Engines|author=N. A. Sinitsyn |journal=J. Phys. A: Math. Theor.|volume=44|year=2011|issue=40 |page=405001|doi=10.1088/1751-8113/44/40/405001|arxiv=1111.7014 |bibcode=2011JPhA...44N5001S|s2cid=119261929 }}</ref> <!-- N.A. Sinitsyn 2011 JPA ''44''' 405001 --> This relation transforms the Carnot's inequality into exact equality. This relation is also a Carnot cycle equality