The performance of the CO2 transcritical refrigeration cycle can be improved

and the throttling irreversibility loss can be reduced

by subcooling CO2 at the outlet of the gas cooler with a vapor compression refrigeration cycle (auxiliary cycle). A thermodynamical analysis is performed to study the operation characteristics of the CO2 transcritical refrigeration cycle with mechanical subcooling

and the results indicate that the maximum coefficient of performance (COP) is achieved at the optimum discharge pressure and optimum subcooling temperature. Compared with the traditional CO2 transcritical cycle

the improvement in COP is more significant at higher ambient temperatures and lower evaporation temperatures

and the discharge pressure and temperature can be notably reduced by the auxiliary cycle. The energy consumption of the auxiliary cycle compressor is much lower than that of the CO2 compressor. Among the 11 auxiliary cycle refrigerants

the differences between the COP improvements of the other 10 auxiliary working fluids are not obvious

except for R41. The CO2 transcritical cascade refrigeration cycle is more applicable to working conditions with higher ambient temperatures and lower evaporation temperatures.