Study On Performance Of Three-level Cascade Refrigeration System With Low Temperature Secondary Refrigerant

Since the 21 st century,with the rapid development of economy and the improvement of people’s living standards,more and more key technologies of industries need to be studied in a special low-temperature environment.In order to obtain a lower temperature,the single-stage compression refrigeration system is obviously not suitable.At present,in order to obtain a lower temperature environment,the stack refrigeration system has become a technical choice to realize its function.Cascade refrigeration systems are considered the main means of obtaining lower temperatures because they improve system performance by using a variety of combinations of refrigerants and lubricants.This paper designed a three-stage cascade refrigeration system experiment platform and used simulation software to analyze the performance of the three-stage cascade refrigeration system,through the use of the experimental platform cooling liquid carrying refrigerant and experimental research on the performance of the experimental platform,the experimental results and simulation comparison,so as to further analyze the performance of the three-stage cascade refrigeration system.Three-level cascade refrigeration system by high-temperature,medium-temperature and low-temperature stage compressor,condenser,evaporator,condenser evaporator,dry filter,oil separator,accumulator,throttling device and so on,using R404 A,R23,R14 as refrigerant of the three-level cascade refrigeration system,using freezing liquid WD-3 as experiment with liquid refrigerant,Through the experiment,the cooling effect of the refrigeration system on the secondary refrigerant is analyzed.The relationship between evaporator inlet and outlet temperature,compressor inlet and outlet temperature,refrigerating capacity,compressor power consumption,COP and liquid secondary refrigerant temperature was studied.At the same time,MATLAB was used to establish a mathematical model of the three-stage overlapping refrigeration system,and the influence of temperature difference between different condensers on COP of the system was analyzed.By changing the evaporation temperature,the changes of suction and exhaust temperature,COP,work done by the compressor and exergic loss of the system were studied with different evaporation temperatures.Finally,the following conclusions are obtained after comparative analysis of experimental results and simulation results:In the process of decreasing evaporation temperature,the simulated value and experimental value of COP of refrigeration system decrease gradually.The experimental and simulated values of the power consumption of the compressors increase gradually,and the experimental values of the power consumption of the three compressors in the system are greater than the simulated values of the three compressors.The exhaust temperature of the three stage cascade compressor is gradually increased in the actual operation and numerical simulation of the system.It is found that when the liquid secondary refrigerant of different mass is used for heat exchange with evaporator,the larger the mass of liquid secondary refrigerant is,the more sufficient the heat exchange effect is with evaporator and the faster the heat exchange rate is.Moreover,when the temperature is low in the refrigeration process of the three-stage cascade refrigeration system,the secondary refrigerant will frost on the surface of the coil in contact with the evaporator,which reduces the heat exchange effect of the evaporator and the secondary refrigerant,resulting in the secondary refrigerant can not reach a lower temperature.