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

It is acknowledged that the Curzon-Ahlborn efficiency eta(CA) determines th e efficiency at maximum power production of heat engines only affected by t he irreversibility of finite rate heat transfer (endoreversible engines), b ur PICA is not the upper bound of the efficiencies of heat engines. This is conceptually different from the role of the Carnot efficiency eta(C) which is indeed the upper bound of the efficiencies of all heat engines. Some au thors have erroneously criticized eta(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, a nd often desirable, for their efficiencies to be larger than their respecti ve 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 fini te time thermodynamics. (C) 2000 Published by Elsevier Science Ltd.