Gu Zhaolin，Liu Hongjuan，Li Yun
(School of Environmental and Chemical Engineering,Xi'an Jiaotong University,Xi'an 710049,China)
Abstract：Studied is a kind of ammonia/carbon dioxide two-stage low temperature refrigeration system, in which ammonia is used as the refrigerant in the high-temperature stage and carbon dioxide is used as the refrigerant in the low-temperature stage. The performance of the system is simulated and analyzed by changing the mean temperature of the evaporator-condenser and the temperature of the condenser. The mean temperatures of the evaporator-condenser are calculated to maximize the coefficient of performance（COP） of the system at different condensing temperatures. It is shown that there exists an optimum mean temperature in evaporator-condenser to maximize the COP of the system，and the maximal COP of the system is increased with lowering the condensing temperature. The relationship between the optimum mean temperature and the condensing temperature is given.
Keywords：carbon dioxide；ammonia；refrigeration system；natural refrigerant