A more general model of endoreversible cycles is constructed on the basis of the models of endoreversible three-heat-source cycles and generalized Carnot cycles. Its optimal configuration and fundamental optimum formula are studied. It is pointed out that the optimum formula may be used to discuss the effect of finite heat source and thermal resistance on the performances of various thermodynamic cycles. Some more significant results than those of classical thermodynamics can be obtained. They may provide some new theoretical bases for the exploitation and application of the new technology of three-heat-source cycles applying low-level heat sources such as solar energy, geothermal energy, waste heat, and so on. Simultaneously, it is also expounded that many important conclusions in the current literature concerned with endoreversible cycles may all be included in the optimum formula. It is thus clear that the formula can make a unified description of various endoreversible cycles discussed in finite-time thermodynamics. Obviously, the major significance of such a description lies in that it can promote the development of finite-time thermodynamics and the establishment of a systematic theory.

• Received 30 September 1988

DOI:https://doi.org/10.1103/PhysRevA.39.4140