Thermodynamic Performance Analysis of CO2 Transcritical Refrigeration Cycle Assisted with Mechanical Subcooling

The thermal performance of CO2 transcrtical refrigeration cycle can be improved by cooling the CO2 fluid exiting the gas cooler with an assisted vapor compression refrigeration cycle (auxiliary cycle). Thus, a thermodynamic analysis is performed to study the operation characteristics of the subcooling CO2 transcritical refrigeration cycle. The results indicate that a maximum COP is achieved at the corresponding optimum discharge pressure and the optimum subcooling temperature. The improvement in COP is more significant in the case of higher ambient temperature and lower evaporation temperature, and the discharge pressure and temperature can be obviously reduced. The auxiliary cycle refrigerant is screened and R717 performs with the highest COP. The CO2 transcritical assisted with mechanical subcooling is recommended for the cases with higher ambient temperature and lower evaporation temperature.