The Study of Using Carbon Dioxide as the Alternative of R502 in Industrial Refrigeration Applications

This paper presents the simulation study and comparison of C02 and R502 as refrigerants. At first, as a single stage vapor compression refrigeration cycle's refrigerant, C02 can be used in subcritical and transcritical situations. The performances are studied completely. The results show that C02 has the same or better performance compared to R502's in certain temperature ranges. Finally C02 and R502's performances in a C02 liquefying system are discussed in detail. It is promising to use C02 as the alternative ofR502 in this case, either in performance or in economics. eq4! h Tamb T, T/e w t c p NOMENCLATURE exergy ofthe cooling capacity kJ/kg enthalpy kJ /kg ambient temperature K evaporating temperature K exergy efficiency work input for compressor kJ /kg condensing temperature 'C pressure MPa INTRODUCTION More than ten years ago, the Montreal Protocol, a real landmark decision to our global environmental protection was agreed by the main industrial nations. Since then, an extensive research work has been done in seeking the alternatives of CFCs and HCFCs. By now, substantial progress has been made in this field. The refrigerants RI34a, R407c, R404a, etc. were regarded as the main alternatives of RI2, R22 and R502 respectively. These new refrigerants have been produced commercially. However, these alternatives do not meet the demands of the long term alternatives. Almost every new alternative has a high greenhouse effect or some other defects. But the natural refrigerants such as C02, NH3, etc. are very excellent in environmental protection121•14l. Therefore using natural refrigerants is becoming more and more important once again. C02, as a refrigerant, can be obtained easily from the natural world. It has been used in many refrigeration machines in history. But the low critical temperature limited its applications, especially when freons were produced in 1930s. Because C02 has a high environmental protection performance, it has been noticed recently. More and more researches have been carried out by using C02 as the alternatives of freons131•151• It is proved that C02 supercritical heat rejection results in a large temperature glide and therefore can be used in heat recovery and heat pump applications. Many studies have investigated the benefits and disadvantages of using C02. Much has been written about the thennodynamic performance. And the applications are still very little. This paper will focus on the