On the Curzon–Ahlborn efficiency and its connection with the efficiencies of real heat engines

Abstract It is acknowledged that the Curzon–Ahlborn efficiency η CA determines the efficiency at maximum power production of heat engines only affected by the irreversibility of finite rate heat transfer (endoreversible engines), but η CA is not the upper bound of the efficiencies of heat engines. This is conceptually different from the role of the Carnot efficiency η C which is indeed the upper bound of the efficiencies of all heat engines. Some authors have erroneously criticized η CA as if it were the upper bound of the efficiencies of endoreversible heat engines. Although the efficiencies of real heat engines cannot attain the Carnot efficiency, it is possible, and often desirable, for their efficiencies to be larger than their respective maximum power efficiencies. In fact, the maximum power efficiency is the allowable lower bound of the efficiency for a given class of heat engines. These important conclusions may be expounded clearly by the theory of finite time thermodynamics.

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