Thermodynamic analysis of a transcritical CO2/propylene (R744-R1270) cascade system for cooling and heating applications

In this paper natural refrigerant propylene (R1270) has been proposed for transcritical cascade refrigeration system and analyzed. Propylene is used in the low temperature (LT) cycle and carbon dioxide is used in the high temperature (HT) cycle of the cascade transcritical refrigeration system. The proposed transcritical cascade cycle can be used for simultaneous cooling and heating applications. Thermal performance of the cascade cycle is evaluated for different combinations of design and operating variables and optimum performance parameters such as Topt, COPmax and mass flow of propylene and CO2 have been predicted. Design parameters include the evaporator temperature of LT cycle (TE), gas cooler outlet temperature (TC) and cascade heat exchanger temperature difference (DT). The results of the analysis show better thermal performance of CO2-propylene transcritical cycle than subcritical cascade cycle and also better than N2O-CO2 transcritical cycle. A methodology to obtain relevant performance diagrams and regression correlations to serve as a guideline for the design and optimization of transcritical CO2-propylene cascade system has been developed.