Fundamental considerations for designing compact solar thermal power and ejector cooling systems in hot climates

A combined thermal power and ejector refrigeration cooling cycle is proposed in this paper to harness low-grade solar energy. It utilizes abundant and low-cost hydrocarbon as the working fluid. Hydrocarbon has been identified as a promising alternative to existing high global-warming-potential refrigerants (i.e., HFC refrigerant R134a) in next-generation refrigeration systems. Several typical alternative refrigerants are evaluated by considering their fundamental thermophysical properties: Absolute pressure level, volumetric cooling capacity, surface tension, saturated liquid/vapor density ratio and kinematic viscosity. Comparing with R1234yf, R1234ze and R744 (CO₂), hydrocarbon refrigerants, such as R290 (propane) and R601 (pentane), do have inherent advantages for either cooling or power generation purposes in hot climates: lower flow resistance and better heat transfer at higher temperature. Fundamental phase stability and transition issues have been considered in designing pentane vapor ejectors for combined power and cooling cycles operating at high ambient temperature. Thermodynamic analysis has indicated that the proposed solar thermal system can provide an effective way to sustainable energy production in hot and dry climates.