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## Carnot heat engine
A Every thermodynamic system exists in a particular state. A thermodynamic cycle occurs when a system is taken through a series of different states, and finally returned to its initial state. In the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. A heat engine acts by transferring energy from a warm region to a cool region of space and, in the process, converting some of that energy to mechanical work. The cycle may also be reversed. The system may be worked upon by an external force, and in the process, it can transfer thermal energy from a cooler system to a warmer one, thereby acting as a refrigerator rather than a heat engine. In the adjacent diagram, from the original 1824 paper by Sadi Carnot entitled ## Additional recommended knowledge
## Modern diagramAbove, we see the original piston-and-cylinder diagram used by Carnot in discussing his ideal engine; below, we see the Carnot engine as is typically modeled in current use: In the diagram shown, the “working body” (system), a term introduced by Clausius in 1850, can be any fluid or vapor body through which heat Q was typically a stream of cold flowing water in the form of a condenser located on a separate part of the engine. The output work _{C}W here is the movement of the piston as it is used to turn a crank-arm, which was then typically used to turn a pulley so to lift water out of flooded salt mines. Carnot defined work as “weight lifted through a height”.
## Carnot's theoremIt can be seen from the above diagram, that for any cycle operating between temperatures
In other words, maximum efficiency is achieved if and only if no new entropy is created in the cycle. Otherwise, since entropy is a state function, the required dumping of heat into the environment to dispose of excess entropy leads to a reduction in efficiency. So Equation 3 gives the efficiency of any reversible heat engine. ## Efficiency of real heat enginesCarnot realised that in reality it is not possible to build a thermodynamically reversible engine, so real heat engines are less efficient than indicated by Equation 3. Nevertheless, Equation 3 is extremely useful for determining the maximum efficiency that could ever be expected for a given set of thermal reservoirs. Although at which heat is input and output, respectively. Replace T in Equation (3) by <_{C}T> and <_{H}T> respectively.
_{C}For the Carnot cycle, or its equivalent, < T> the lowest. For other less efficient cycles, <_{C}T> will be lower than _{H}T , and <_{H}T> will be higher than _{C}T. This can help illustrate, for example, why a reheater or a regenerator can improve thermal efficiency.
_{C}*See also: Heat Engine (efficiency and other performance criteria)*
## Notes**^**Carnot, Sadi (1824).*Réflexions sur la Puissance Motrice du Feu*, page 17.
## References- Kroemer, Herbert; Kittel, Charles (1980).
*Thermal Physics*, 2nd ed., W. H. Freeman Company.__ISBN 0-7167-1088-9__.
## See also |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Carnot_heat_engine". A list of authors is available in Wikipedia. |