Exergy Analysis of Solar Rankine Power Cycles Used for Cooling.

摘要

Second-law (exergy) analysis was performed on two types of solar-cooling systems which are based on a vapor-compression cycle driven by a Rankine cycle: those energized by the sun at one temperature and using organic fluids in the power cycle, and a hybrid cycle which is energized by a solar source at a low temperature and by a fossil source at a higher temperature and using steam as the fluid. Some of the major conclusions are: (1) A better thermodynamic match is obtained between the energy sources and sinks in the hybrid cycle, which results in a doubling of the cycle's efficiency as compared to the single-temperature organic-fluid cycle. Nevertheless, there still exists a large difference between the temperatures of combustion (approx. 1500 exp 0 C) and superheated steam (approx. 600 exp 0 C), and thus the superheater's effectiveness is relatively low. This points to several methods of improvement, including improved heat-transfer design, and utilization of the stack gases. (2) Applying superheat by solar concentrators instead of combustion improves cycle effectiveness by about 40%, and (3) the heat exchangers to recover heat from the steam after it has been exhausted from the turbine have an important influence on energy and exergy recovery but need to be carefully optimized. (ERA citation 08:038807)