Performance study on a vapour compression refrigeration cycle using R744/R290, R744/R600 or R744/R600a as refrigerant

The high pressure in transcritical refrigeration cycle using pure R744 (CO2) as refrigerant is conventionally up to 10MPa, which exerts rigorous demands upon CO2 components, refrigerating system and its safe operation. Consequently, it is a possible disadvantage that the initial cost of pure CO2 based refrigeration system is higher than that of conventional refrigerants. To decrease high pressure, meanwhile not to affect the global environment, Natural refrigerant mixtures, which are environmentally friendly, are taken in this research. Under the given conditions, theoretical analyses on a vapour compression refrigeration cycle were conducted to investigate the system performance when using R744/R290, R744/R600 or R744/R600a as naturally non-azeotropic refrigerant mixtures. For three mixtures, by altering mass fraction of CO2 and refrigerant temperature at evaporator exit respectively, the influences of which upon cooling capacity, heating capacity, compressor power and condensing pressure were performed. Calculation results show that one of the advantages of this system is the capability of keeping the high pressure in the system within a range of the common vapour compression refrigeration system by selecting the CO2 fraction of mixture when compared to that in the vapour compression system using pure CO2. R744/R600 or R744/R600a has a lower condensing pressure but a poor COP while R744/R290 is opposite under the same conditions. As the mass composition of R744 in the mixture increases, COP decreases and compressor power increases.