Theoretical And Experimental Study On A Variable Temperature Refrigeration System Based On Non Azeotropic Refrigerant

The world energy crisis and environmental pollution has become a major challenge to all human beings in the present situation.How to realize building energy conservation and reduce carbon emission are of great significance to the harmonious development between man and nature.Because the temperature and humidity independent control air-conditioning system has high energy efficiency ratio and better comfort,It has good prospects for development.Therefore,a variable temperature refrigeration system based on non-azeotropic mixtures refrigerants is developed for temperature and humidity independent control air conditioning system in this dissertation.Three environmentally friendly refrigerants R32/R236fa,R32/R600and R1270/R600,are used to produce low-temperature chilled water?outlet temperature6?-8??and high-temperature chilled water?outlet temperature 16?-18??.The non-azeotropic mixtures refrigerant variable temperature refrigeration system has the characteristics of energy efficient utilization through theoretical and experimental researches.It also has a wide range of applications and higher application value.The specific contents and conclusions are as follows:The performance calculation model of variable temperature refrigeration system based on non-azeotropic mixtures is established.The composition and components of non-azeotropic mixtures refrigerants are selected according to the characteristics of the refrigeration system,as for as the boiling point of pure refrigerant,and the influence of saturated vapor pressure and temperature glide of mixed refrigerants,on the basis of comprehensive physical parameters such as environmental protection of mixed refrigerants.The method for selecting the components of mixtures with glide temperature based on the minimum entropy method is established based on the analysis of the irreversible loss of phase change heat transfer of non-azeotropic mixtures,The performance parameters of the refrigeration system are compared with those of four conventional refrigerants.The energy-saving potential of the temperature and humidity independent control air-conditioning system based on non-azeotropic refrigerant mixtures is analyzed,which provides an important theoretical basis for the subsequent experimental study of the refrigeration system.The performance test-bed for variable temperature refrigeration system based on non-azeotropic mixtures was established,and the performance of the refrigeration system was tested by using a variety of composition of three mixtures.Including different components in the same composition and mixed refrigerants with different composition.The optimum performance parameters of refrigeration system includes low-temperature refrigeration capacity,high-temperature refrigeration capacity,the ratio of low-temperature refrigeration capacity to high-temperature refrigeration capacity,total refrigeration capacity and compressor power consumption,total COP,low temperature COP,high temperature COP,exhaust temperature,suction and exhaust pressure,compression ratio and so on.The effects of mixing refrigerant composition,mixing refrigerant bubble and dew point temperature,mixing refrigerant glide temperature,low and high temperature chilled water temperature on the performance of refrigeration system are studied by combining theory with experiment.It provides data support for the high application value of variable temperature refrigeration system with non-azeotropic mixtures.The characteristics of non-azeotropic refrigerant mixtures system using chilled water in series are studied.by R407C,R1270/R600,R32/R236fa and R32/R600 under various operating conditions such as the outlet chilled water temperature is 5?,6?,7?and the inlet temperature is 16?,17?respectively.The wide applicability of the non-azeotropic refrigerant refrigeration system is verified.The temperature distribution of three composition mixed refrigerants in heat exchangers is analyzed theoretically based on the nonlinear variation of temperature with enthalpy value.Both the effects of working fluid composition and heat sink temperature difference on the pinch point in condenser and the maximum heat transfer temperature difference in evaporator are discussed.The practicability of the method on optimizing the composition of mixed refrigerants with large glide temperature based on the minimum entropy method is verified by experimental study.The theoretical study of temperature difference heat transfer exergy efficiency and glide temperature transfer exergy efficiency during phase change heat transfer of non-azeotropic mixtures is carried out.The calculation model based on transfer exergy efficiency?_glide?temperature matching coefficient?parameters is established,and the effect of temperature matching coefficient of mixtures on phase change heat transfer of mixtures is analyzed..Then the correctness of the model is verified by experiments.The method of series connection of low and high temperature chilled water was adopted on the variable temperature refrigeration system based on non-azeotropic mixtures refrigerants.