Thermodynamic analysis of the combined organic flash and ejector refrigeration cycle using zeotropic mixtures

Recently, the combined power and cooling (CPC) cycle has attracted more and more attention due to its higher overall efficiency and diversified energy output. However, the existing CPC cycles cannot guarantee a good temperature matching between the cycles and heat sources and sinks at the same time, which leaves some room for improvement in the CPC cycles. In this study, according to the temperature matching principle, three basic requirements that CPC cycles should meet under ideal conditions are clearly stated for the first time. After that, a novel CPC cycle that can meet these requirements is proposed by integrating the organic flash cycle, ejector refrigeration cycle, internal heat exchanger, and zeotropic mixtures. To study the performance of the proposed CPC cycle using R600a/R601a mixtures in the geothermal application, energy and exergy analysis is conducted. Results show that the maximum exergy efficiency of the proposed CPC cycle using R600a/R601a mixtures is 36.34 %, which is 1.34 % and 3.38 % higher than that using pure R600a and R601a, respectively. Moreover, when the exergy efficiency of the proposed CPC cycle is maximum, the sum of the exergy destruction of the heater, condenser, and evaporator using R600a/R601a mixtures is 17.92 kW, which is 4.23 % and 7.93 % less than that using pure R600a and R601a, respectively.