| CFCS and other synthetic refrigerants, that are used in refrigeration industry, caused serious damage to the Earth’s ozone layer. Subsequent development HCFCS class of synthetic refrigerants damage to the ozone layer while smaller, but they have impact on the earth with different degree of the greenhouse effect. Due to the issue of global warming, refrigeration industry has done a lot of experimental study to seek alternative refrigerants, in which carbon dioxide is favored with its good physical, chemical properties. R404a is environmental protection refrigerants, and CO2is a natural working substance. Along with the social development and the protection of the human survival environment, they will be widely used.Based on analysis of the cascade refrigeration and natural,environmental refrigerants, R404a/CO2cascade refrigeration system has designed, and carried on the theoretical analysis and design selection, that provides the reference to alternative of natural refrigerants in the cascade refrigeration system.The main contents of the first chapter is to propose the research background, to describe the purpose and significance of research, to summarize the main research contents, and to outline the basic framework of the paper. Secondly the paper introduces R404a and CO2and the development situation of environmentally friendly refrigerants and physical characteristics, and to study and understand the application areas and the role of CO2. The third chapter has introduced R404a/CO2cascade refrigeration system. Combined with the related theory the principle and workflow of the system is decried, and R404a/CO2cascade refrigeration unit mathematic model is established, and the design key points and technical advantages of the cascade refrigeration system. The fourth chapter is the system design, firstly, theoretical calculation is done by using mathematical model, then the various components of the system is determined. The fifth chapter describes conclusion and prospect. |
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