Performance Study On CO₂ Dual Temperature Refrigeration System With Multi-ejector

The natural refrigerant CO₂ has received more and more attention and application as a refrigerant because of its low GWP and zero ODP.However,under the condition of high ambient temperature the throttling process in the traditional CO₂ transcritical cycle results in greater pressure loss and lower COP of the system.In order to reduce the pressure loss a new type of CO₂ refrigeration system was adopted in this paper,that is,the multiple parallel ejectors are used to replace the traditional throttling device,and the parallel compressors are added at high pressure side to form the dual-temperature refrigeration system with multi-ejector.The theoretical and experimental research on the system is of great significance and application value for the CO₂ dual-temperature refrigeration system with multi-ejector.First of all,the mathematical model of the components of CO₂ dual-temperature refrigeration system with multi-ejector is established,and the system simulation program was compiled by using MATLAB software.The effects of mass flow ratio of medium temperature and low temperature evaporators on the performance of the traditional booster refrigeration system（CBR）and refrigeration system with multi-ejector parallel ejector refrigeration system（MECR）were calculated theoretically.The influence of the outlet temperature and pressure of the gas cooler on the performance of the systems was analyzed under different intermediate pressure conditions in MECR system.Secondly,the performance of the CO₂ dual-temperature refrigeration system with multi-ejector is verified by experiments,and the effects of the mass flow ratio of medium temperature and low temperature evaporators in CBR system and MECR system on the performance of the systems were explored.The effects of parallel compressors in MECR system on system performance were compared and analyzed.Finally,the theoretical simulation data were compared with the experimental results.The main conclusions of the simulation and experimental results are as follows:（1）The simulation results show that in both CBR and MECR systems,under the same operating conditions,with the increase of the mass flow ratio of medium-temperature and low-temperature evaporators the refrigerating capacity and COP of the system are increasing,and the power consumption of the system remains unchanged.With the increase of the outlet pressure of the gas cooler,the power consumption and refrigerating capacity of the system increases,while COP decreases.（2）The simulation results show that in the MECR system,for the fixed medium temperature low temperature evaporation temperature and the gas cooler outlet temperature,under the same outlet pressure of the air cooler with the increase of the intermediate pressure,the ejection ratio of the system decreases gradually,and the power consumption of the system decreases linearly,while the cooling capacity and COP of the system increase at first and then decrease,and reach the maximum when the intermediate pressure is4.0Mpa.At the same outlet temperature of the gas cooler,with the increase of the intermediate pressure,the changing trend of the injection ratio,power consumption,refrigeration capacity and COP of the system is the similar as that under the same outlet pressure of the gas cooler.Under different outlet pressure and temperature of the gas cooler,the cooling capacity and COP of the system reach the maximum at the intermediate pressure of 4.0Mpa.The higher the outlet pressure of the gas cooler,the higher the refrigerating capacity and COP of the system,while the higher the outlet temperature of the gas cooler,the lower the refrigerating capacity and COP of the system.（3）The experimental results show that under the same other operating conditions the cooling capacity,COP and power consumption of the system increase with the increase of the mass flow ratio of the medium temperature and low temperature evaporators in both CBR and MECR systems,while the power consumption of the low pressure stage is basically unchanged.With the increase of mass flow ratio of the medium temperature and low temperature evaporators,the ejector ratio in MECR system is also increasing.The COP of MECR system is up to 23.77%higher than that of CBR system.（4）The comparation experimental results show that under the same working conditions,with the change of the outlet temperature of the gas cooler,with and without parallel compressor on the MECR system,the change trend of the parameters of the two systems is the same.While the system performance of the system with parallel compressor is better than that of the system without parallel compressor,and the COP can be improved by 6.89%.（5）The experimental results and simulation results show that under the same working conditions,in CBR system and MECR system,with the change of mass flow ratio of medium temperature and low temperature evaporators,the trend of cooling capacity and COP of experimental results are consistent with the simulation results as a whole.The comprehensive performance of MECR system is better than that of CBR system.