Alternative refrigerants request satisfy the ozone layer protection and stop global warming up the dual requirement. The
former IIR chairman G. Lorentzen [1]is the first to advance the CO2 transcritical cycle, and think that CO2 is "the most
prospects refrigerant of the 21st century." CO2 as a refrigerant, has its unique advantages [2], but the COP of the transcritical system is not high because of their lower critical temperature (31℃). Therefore, the key to promote the CO2 transcritical cycle is to improve the efficiency of the system. Natural refrigerants are increasingly becoming the refrigerant of
choice to replace the environmentally harmful CFCs and (H)CFCs. CO2 is the most friendly with the environment, it is one
of the refrigeration laser has many advantages: