Performance Evaluation of Vapor Compression Refrigeration System using CO2/Propane and CO2/Propylene Mixtures

The search for low GWP refrigerants has become a critical area of research in response to climate change. Natural refrigerants such as carbon dioxide (R744), propane (R290), and propylene (R1270) are particularly promising due to their low GWP. This study theoretically investigates the use of zeotropic mixtures of R744+R290 and R744+R1270 as refrigerants in a vapor compression refrigeration cycle with an internal heat exchanger. A performance analysis of these mixtures was conducted, and the maximum COP and VRC values were investigated according to the compressor discharge pressure (PH). The effects of ambient air temperature and the mole fraction of R744 on cycle performance were also examined. The results indicate that the R744+R1270 mixture achieves COP and VRC values, on average, 16.5% and 12.2% higher, respectively, than those of the R744+R290 mixture. Furthermore, the optimal compressor discharge pressure for R744+R1270 is, on average, 240 kPa lower than that for R744+R290. When the mole fraction of R744 exceeded 0.6, the lower flammability limit of the mixture increased exponentially. For mole fractions of R744 above 0.36, the maximum COP of the R744+R290 mixture was lower than that of pure R744. An increase in ambient air temperature resulted in a linear rise in the optimal compressor discharge pressure, accompanied by a reduction in both the maximum COP and VRC.