Theoretical Analysis And Experimental Research On R404A/CO₂ Cascade Refrigeration System

In this paper, a new type R404 A /CO₂ cascade refrigeration system which designed for-40 ℃ evaporation temperature to refrigerated foods not only meeting the demand of people’s lives and environmental protection and energy saving in commercial refrigeration applications is established.The goal of this study is to get a comprehensive understanding of its performance based on the theoretical analysis and experimental research. First,it is introduced the research progress of cascade refrigeration system in recent years. Especially introduce the cascade refrigeration systems which uses carbon dioxide as the refrigerant of the low-temperature circuit and udes NH3、R290、R134A、R404A the refrigerant of the high-temperature circuit, respectively.The research progress shows that the cascade refrigeration cycle system with CO₂ as the low-temperature circuit refrigerant has a very good development prospect.It analyzes the design parameters including the evaporating temperature,the condensing temperature,the temperature difference in the cascade-condenser,the degree of superheat,the degree of subcooling and others for system performance relationship. The result concludes that under certain conditions, the higher the evaporating temperature, condensing temperature is lower, the temperature difference in the cascade-condenser, the greater the compressor suction superheat, the greater the subcooling,the system COP get higher. In addition, the evaporating temperature and subcooling is one of the largest factors affect system’s COP. At the same time, This paper describes the two-stage refrigerant system utilizing R404 A as refrigerant : R404 A / CO₂ cascade refrigeration system and R404 A two-stage compression utilizing CO₂ as secondary refrigerant system. Compared with the two systems, it finds that they have maximum system COP and maximum COP increases with the heat-transfer temperature difference of condensing evaporator increases and decreases with the evaporating temperature increases. Meanwhile, the two-stage compression system has the great superiority in saving refrigerant than the cascade system when the evaporating temperature below-30℃. However, the cascade system COP is higher than R404 A two-stage compression utilizing CO₂ as secondary refrigerant system 10.2%.In this paper,it is built that a test rig for the R404 A /CO₂ cascade refrigeration system which designed for low evaporation temperature in commercial refrigeration applications. The main research work is that the relation about the COP and performance of compressor with some parameters which are condensing temperatures from 30 to 50 ℃,evaporating temperatures from-30^-50℃ and temperature difference in the cascade heat exchanger from 3⁸℃. The results show that the R404 A suction superhea of R404 A /CO₂ cascade refrigeration systemt control between 4 6 ℃ is advantageous to the optimization of the system.The key to increase the COP of the system is improving the efficiency of compressor capacity.Finally it uses R41 refrigerant replaced CO₂ filling in the compressor of the lowtemperature cycle in this cascade refrigeration system device.Compared the R404A/R41 cascade refrigeration system and R404A/R23 cascade refrigeration system which get the date from existing literature of experimental data in low temperature field,find that the performance of R404A/R41 cascade refrigeration system was higer 14.5% than R404A/R23 cascade refrigeration system when the evaporating temperatures is-65℃.