Numerical Simulation And Experimental Study Of Dual-temperature CO₂ Refrigeration System With Multi-ejector

In the traditional transcritical CO₂ refrigeration system,the throttling loss is serious as a result of the high operating pressure of the system.The ejectors are widely used in various refrigeration systems to recover low-grade expansion work.Multi-ejector is a device that works in parallel with several ejectors of fixed geometric size,and its regulating function is more flexible,which can meet the changing demand of refrigerant mass flow in the system under different working conditions.In this paper the CO₂ dual-temperature refrigeration cycle system with the multi-ejector is studied.In this system,the multi-ejector is used to replace the traditional high-pressure valve,and part of the low-grade expansion work can be recovered to reduce the irreversible loss during the throttling process and generate additional cooling capacity,which in turn improves the system COP,it can meet the demand for refrigeration and refrigeration in commercial supermarkets.In this paper a mathematical model is established for the main components of the dual-temperature refrigeration system with the multi-ejector by using the method of the lumped parameter method.The performance of the system is simulated and studied with Matlab programming language.The effects of gas cooler outlet temperature,gas cooler outlet pressure,parallel compressor,system intermediate pressure,and intermediate,low-temperature evaporation temperature on the performance of the refrigeration system were analyzed.On the basis of the experimental platform of the multi-ejector circulation refrigeration system built by the previous members of the research group,the experimental work of the dual-temperature refrigeration circulation system was carried out.The influence of refrigeration system performance,and the experimental results and simulation results are compared,the main conclusions are as follows:（1）The simulation results show that: under the same working conditions,using multi-ejectors instead of high-pressure valves can effectively recover part of the expansion work,increase the system cooling capacity and increase the system COP.The cooling capacity increases by about 9.2%³1.1%,and the COP increases by about 9.5%³5.14%.（2）The simulation results show that when the evaporating temperature and the air cooler outlet pressure in the dual temperature zone are constant,the system cooling capacity and COP increase first and then gradually decrease due to the air cooler outlet temperature.The corresponding outlet temperature of the air cooler is also higher.（3）The simulation results show that when the temperature evaporation temperature in the dual temperature zone and the outlet temperature of the gas cooler are constant,under the influence of the outlet pressure of the gas cooler,the total power and cooling capacity of the system are gradually increasing;at a higher outlet temperature of the gas cooler,the system COP follows the air cooling The rise of the outlet pressure of the radiator showed a trend of first increasing and then decreasing.There is an optimal outlet pressure of the gas cooler in the system.At this time,the COP reaches the maximum value.（4）The simulation results show that when operating in multi-ejector mode,the use of an auxiliary high-pressure compressor can reduce the flash gas in the sub-high vapor-liquid separator,increase the system circulation mass flow,reduce the system power consumption,and then improve the system cooling capacity and COP.（5）The experimental and simulation results show that under the same working conditions,the multi-ejector dual-temperature refrigeration system has the best intermediate pressure,and at the optimal intermediate pressure of the system,the cooling capacity and COP of the system both get the maximum value.On the whole,the experimental results are consistent with the simulation results.（6）The experimental and simulation results show that under the same working conditions,under the influence of the evaporation temperature at medium temperature,the system cooling capacity and COP both increased with the increase of the evaporation temperature at medium temperature.Under the influence of low temperature evaporation temperature,the cooling capacity of the system decreases slowly,while the COP increases gradually.On the whole,the experimental results are consistent with the simulation results.