Study On Performance Of CO₂ Multi-Ejector Dual-Temperature Refrigeration System With Internal Heat Exchanger

The COP of the traditional transcritical CO₂ refrigeration cycle is relatively low resulting from its high throttling loss.The multi-ejector,which consists of several parallel ejectors with fixed geometrical dimension,is used as the throttling device in the CO₂ dual-temperature refrigeration system to recover the expansion work,so as to increase the refrigeration capacity and system COP.The use of the internal heat exchangers can increases the refrigeration capacity of the system,but at the same time increases the total power consumption of the system.In this paper the performance of the CO₂ multi-ejector dual-temperature refrigeration system with low and high temperature internal heat exchangers is simulated and studied experimentally,and the effects of the main factors are analyzed.The study on improvement for the performance of CO₂ supermarket refrigeration system is of important theoretical significance and practical value.In this paper,the lumped parameter method was used to establish the models of each components of the CO₂ traditional refrigeration system and the CO₂ multi-ejector refrigeration system,and the program was compiled using MATLAB to simulate the performance of the CO₂ traditional refrigeration system and the CO₂ multi-ejector refrigeration system.Under different gas cooler outlet temperature and pressure conditions,the improvement degree of the system performance caused by the use of high temperature and low-temperature internal heat exchangers were analyzed.In order to verify the influence of the high-temperature internal heat exchanger on the performance of the CO₂ traditional refrigeration system and the CO₂ multi-ejector refrigeration system,under different gas cooler outlet temperature and pressure conditions,the effect of the use of the high-temperature internal heat exchanger on the system performance was studied experimentally.Comparing the experimental and simulation results,the main conclusions are as follows:（1）The simulation results show that the use of the low-temperature and high-temperature internal heat exchangers can improve the performance of the CO₂ traditional dual-temperature refrigeration system and the CO₂ multi-ejector dual-temperature refrigeration system,and the performance improvement of the multi-ejector refrigeration system is slightly greater than that of the CO₂ traditional refrigeration system.Under the simulation condition in this paper,due to the use of the low-temperature internal heat exchanger,the total refrigeration capacity of the CO₂ traditional refrigeration system and the multi-ejector refrigeration system is increased by10.15%-13.03%and 11.55%-14.35%,respectively,and the COP of the CO₂ traditional refrigeration system is increased by up to 5.84%,while the COP of the CO₂ multi-ejector refrigeration system is increased by up to 6.51%.By using high-temperature internal heat exchanger,the total refrigeration capacity of the CO₂ traditional system and CO₂ multi-ejector refrigeration system is increased by 9.69%-71.98%and 12.18%-74.13%,respectively.The COP of traditional system and multi-ejector system is increased by up to4.34%and 8.21%respectively.（2）The simulation and experimental results show that the use of multi-ejector improves the performance of CO₂ refrigeration system.The simulation results show that under the same working conditions,the COP of the multi-ejector system is increased by24.88%～40.45%compared with the CO₂ traditional refrigeration system;and the experimental results show that under the same working conditions,compared with the CO₂ traditional refrigeration system,the COP is increased by 24.88%～40.45%.The COP of the CO₂ multi-ejector refrigeration system is increased by 7.53%～15.45%.（3）The experimental results show that the high-temperature internal heat exchanger can improve the performance of the CO₂ traditional dual-temperature refrigeration system and the CO₂ multi-ejector dual-temperature refrigeration system.Under the experiment condition in this paper,after using the high-temperature internal heat exchanger the total refrigeration capacity of the CO₂ traditional system and the CO₂ multi-ejector refrigeration system is increased by 1.35%-9.87%and 2.64%-9.41%,respectively.The COP of the CO₂ multi-ejector refrigeration system is increased by 2.95%,and traditional CO₂ refrigeration system is increased by 2.71%.（4）The experimental results show that the total power consumption increases by3.57%-13.24%and 2.17%-15.24%,respectively by use of the high-temperature internal heat exchanger in the CO₂ traditional refrigeration system and the CO₂ multi-ejector refrigeration system.Under the same working conditions,compared with the traditional CO₂ refrigeration system,the total power of the system decreases by 4.28-9.64%by use of the multi-ejector in the CO₂ refrigeration system.