Simulation Study Of Cascade/Ejection Refrigeration Cycle Utilizing Compression Exhaust Heat

In recent years,the application and development of ammonia refrigeration technology have been hit by the frequent occurrence of ammonia cold storage accidents,and the refrigeration cycle system by ammonia and carbon dioxide dual working fluid are becoming a promising direction in the new technology of ammonia refrigeration research,because it can perfectly solve the problems of direct contact between ammonia refrigerant and cold storage.Besides,the ejector has a simple structure and can utilize waste heat,and was early used for low-grade heat source driving,so the vapor compression refrigeration cycle coupled with ejector can not only recover the throttling loss,but also utilize the exhaust heat of compressor in refrigeration system.Under this in mind,this paper will design a CO₂/NH₃ jet cascade refrigeration system that can not only solve the problem that flash steam interfere the evaporative heat transfer in the general vapor compression refrigeration cycle to improve the cooling effect and reduce the power consumption of the compressor per unit volume,but also use the exhaust heat of the compressor to improve the efficiency of the system.According to the experimental data in the literature^[1],the ejector,the core part of the system,is verified,and the error between the simulated value and the experimental value almost can be controlled within±10%,which describe the degree of fitting model is better.Then the specific analysis of the system is as below:?1?Comparing with the ordinary cascade system,the simulation results show that the CO₂/NH₃ jet cascade system will better reflect its advantages of improvement and energy-saving significance under the situation of lower evaporation temperature,higher generation pressure,and retaining reheated or overcooled.Specifically,when the evaporation temperature is-55°C and the generation pressure is 7 MPa,the coefficient of performance of the system can be increased by more than 10%compared with ordinary cascade system.Therefore,it can do provide a feasible scheme for further reforming of the ammonia cold storage.?2?Considering the difference in energy quality and the limitations of the first thermodynamic law in the system,the entropy theory is introduced to compare the entropy production between the system and the ordinary cascade system.It is found that the irreversible loss of the evaporative condenser,condenser,low temperature compressor and low temperature throttle valve are effectively reduced,and if the pressure is higher and the evaporation temperature is lower,the trend of decreasing the total entropy of the system will be more obvious,so the suitable working conditions of the system in terms of energy use are further verified.The distribution area of irreversible loss under different working conditions is determined by analyzing the entropy production of each part of the system.Four main components of the CO₂/NH₃ jet cascading system are obtained:evaporator,generator,high temperature compressor and low temperature compressor.Therefore,it can provide better theoretical suggestions for the system to reduce the consumption of energy and entropy further.?3?Compared with entropy,the exergy analysis,which is also based on the second law of thermodynamics and can describe the energy quality concept more clearly and intuitively,and the algorithm specification is simple,has a broader use in engineering application.Firstly,the energy use of the system and the energy saving potential of the system are revealed by comparing it with the internal and external irreversible losses of the ordinary cascade refrigeration system.Secondly,by analyzing the condition of exergy consumption of every part of the system,the amount of exergy uses and distribution of every link in the system cycle are obtained specifically,and focus on the generator,which is the most important component in the system exergy efficiency analysis,to provide the direction for further optimization of the system.Finally,through the analysis of the total exergy efficiency of the system,it is proved that the performance of the system in this paper is superior to the ordinary cascade system.