Efficiency of Real Heat Engines
Carnot realized that in reality it is not possible to build a thermodynamically reversible engine, so real heat engines are less efficient than indicated by Equation (1). Nevertheless, Equation (1) is extremely useful for determining the maximum efficiency that could ever be expected for a given set of thermal reservoirs.
Although Carnot's cycle is an idealisation, the expression of Carnot efficiency is still useful. Consider the average temperatures,
at which heat is input and output, respectively. Replace TH and TC in Equation (1) by <TH> and <TC> respectively.
For the Carnot cycle, or an equivalent, <TH> is the highest temperature available and <TC> the lowest. For other less efficient cycles, <TH> will be lower than TH, and <TC> will be higher than TC. This can help illustrate, for example, why a reheater or a regenerator can improve the thermal efficiency of steam power plants — and why the efficiency of combined-cycle power plants (which incorporate gas turbines operating at even higher temperatures) exceeds that of conventional steam plants.
According to the second theorem, "The efficiency of the carnot engine is independent of the nature of the working substance".
- See also: Heat engine (efficiency and other performance criteria)
Read more about this topic: Carnot Heat Engine
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