1 7 Ja n 20 09 Universality of efficiency at maximum power
نویسندگان
چکیده
The concept of Carnot efficiency is a cornerstone of thermodynamics. It states that the efficiency of a cyclic (“Carnot”) thermal engine that transforms an amount Qr of energy extracted from a heat reservoir at temperature Tr into an amount of work W is at most η = W/Qr ≤ ηc = 1−Tl/Tr, where Tl is the temperature of a second, colder reservoir. The theoretical implications of this result are momentous, as they lie at the basis of the introduction by Clausius of the entropy as a state function. The practical implications are more limited, since the upper limit ηc (“Carnot efficiency”) is only reached for engines that operate reversibly. As a result, when the efficiency is maximal, the output power is zero. By optimizing the Carnot cycle with respect to power rather than efficiency, Curzon and Ahlborn found that the corresponding efficiency is given by ηCA = 1 − √
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