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. Mathematically, this is because in reversible processes, the change in entropy of the cold reservoir is the negative of that of the hot reservoir (i.e., ΔSc = – ΔSh ), keeping the overall change of entropy zero.
The Carnot efficiency is expressed as shownRelated formulas
|ηmax||carnot efficiency (theoretical maximum efficiency) (dimensionless)|
|Tc||absolute temperature of the hot source (K)|
|Th||absolute temperature of the cold source (K)|