The unified cycle model of a class of solar-driven heat engines and their optimum performance characteristics

The unified cycle model of a class of solar-driven heat engines is presented, in which the heat loss of the solar collector and the external and internal irreversibilities of the heat engine are taken into account and used to investigate the optimal performance of the cyclic system. The maximum overall efficiency of the system is calculated. The optimally operating temperature of the solar collector, the optimal temperatures of the cyclic working substance, and the optimal ratio of the heat-transfer areas of the heat engine are determined. The influence of the heat loss of the solar collector and the external and internal irreversibilities of the heat engine on the cyclic performance is discussed in detail. Some important characteristic curves are given. It is more important that the results obtained from the unified cycle model are very general and useful, from which the optimal performance of the solar-driven Brayton, Braysson, and Carnot heat engines and some solar-driven heat engines can be directly derived.