Design And Study On R134a/R744Cascade Refrigeration System

At present, the comprehensive level of manufacturing technology of cold chain equipment is well below the demand of the community. And that has become a bottleneck problem of environmental friendly commercial refrigeration products industrialization. Based on the current problems of industry development of cold chain logistics, a design of energy saving, safety and reliability carbon dioxide cascade commercial refrigeration unit has been proposed, which combines the dual temperature controlling technology. Carbon dioxide cascade commercial refrigeration unit uses natural refrigerant R744as the low temperature cycle refrigerant and uses R134a as the high refrigerant. The unit has a high temperature evaporator and a low temperature evaporator, which can provide two different temperatures of frozen and refrigerated concurrently. With compressors connected in parallel, it can precise control the ambient temperature and better adapt to the change of heat load. When the unit break off, security cold source system started working and adjusted to the pressure of low temperature circulation loop, that improve the safety and reliability of the unit. The main contents are as follows. The urgency and necessity of research and development on new generation of environmental friendly CO2commercial refrigeration unit were demonstrated by analyzing the development situation and related technologies of cold chain logistics industry. In addition, a CO2cascade commercial refrigeration system was proposed. R134a/R744cascade refrigeration system was designed detailed under the specific design was determined, which include the system design, components selection and the development of the experimental program. A thermodynamic analysis was presented to optimize the design an operating parameters of the system after the theory mathematical model of R134a/R744cascade refrigeration system was established. These parameters considering include evaporating temperature of CO2, condensing temperature of R134a and temperature difference of the cascade heat exchanger. The result shows that:the COP of R134a/R744cascade refrigeration system increases with the rising of CO2evaporating temperature,, while decreasing with the increasing of R134a condensing temperature and cascade heat exchanger temperature difference. Moreover, the optimal COP of R134a/R744cascade refrigeration system is2.04, the condensing temperature of CO2is adout-4degree right now. Comprehensive analysis show that the development and research of R134a/R744cascade refrigeration system has an important significance and broad application prospect for the cold chain logistics industry’s development.