Design Of Experimental Setup And Performance Study Of CO₂ Double Temperature Refrigeration System With Multi-Ejectors

A new type of "two-temperature CO2" refrigeration cycle system was studied in this paper,the multi-ejector is instead of the throttle valve to recover the expansion work in the throttling process in this system.There is a great potential of mechanical energy recovery and performance improvement in the CO2 refrigeration system due to its high pressure in transcritical system and large pressure difference before and after throttling.The multiejector is a component used in parallel with different flow capacity of ejectors.Compared with the single ejector system,the multi-ejector system has more flexible adjustment function,which can adapt to the change of mass flow inside the system under different working conditions and improve the recovery efficiency of expansion work under different working conditions,so as to greatly improve the performance coefficient of the refrigeration system and expand the application scope of the CO2 system.Firstly,the schematic diagram of the system operation was designed according to the design requirements,the mathematical model of the main components in the system was settled,and the performance of the multi-ejector CO2 cycle and the traditional expansion CO2 cycle were simulated by Matlab.And then,according to the requirements of the system,The multi-ejector refrigeration setup was designed and built with CO2 as the refrigerant.The setup can be used for the experimental study of multi-ejector CO2 double-temperature refrigeration system,and has the function of running the traditional refrigeration cycle with expansion valve.According to the design requirements of the setup,the selection calculation of the system compressor,heat exchanger,electronic expansion valve and system auxiliary equipment is carried out.The mass flow range of the setup was determined according to the previous study and literature data of the two-phase flow ejector study group,and the basic size of the ejector was calculated theoretically.Four ejectors,including three gas ejectors and one liquid ejector,were designed according to the binary principle of flow capacity.The measurement and control equipment of pressure sensor,temperature sensor and power meter is described in detail in the CO2 refrigeration system.The water cooling system of the CO2 refrigeration cycle cooling system consist of cooling water system which is used to cool air cooler,the medium temperature chilled water is used to absorb the heat of the medium temperature evaporator and the low temperature chilled water system which is used to absorb the heat of the low temperature evaporator.The cooling water and the medium temperature chilled water systems are provided by existing water system in the laboratory.The low temperature chilled is provided by a water tank.Finally,After the completing construction of setup,the setup was started up and running.According to the problems in the experiment,the setup was debugged and improved.The problems encountered in the process of operation were described and the improved methods were proposed.The setup operated steady and normally finally.Based on the simulation and experimental results,the changes of COP and power consumption in two modes of the traditional expansion cycle and the multi-ejector cycle are compared and analyzed in this paper.The following conclusions can be obtained from the experiment and numerical simulation :(1)The parameters of the setup are stable in operation condition,and can operate normally and stably according to the set air cooling pressure and evaporation pressure.The measurement results of refrigerant flow rate,temperature and pressure are accurate and meet the design requirements.(2)The experiment system of the numerical simulation results are consistent with the experimental results,but the result of the simulation and experimental data has large difference,this is because in the process of simulation,the applied scope of associated is limited,the irreversible factors exist in the system at the same time,the research group need to continue to optimized the mathematical correlations in the future.(3)The maximum COP of the multi-ejector CO2 refrigeration cycle system is 2.49,which is higher than that of the traditional refrigeration cycle.The main reason for this phenomenon is that the multiejector recovers some expansion work in the throttling process.(4)The parallel compressor in the system can further improve the system performance,and the system control mode is the key to improve the system performance.