Performance Investigation And Optimization Of A Rotary Compressor With Refrigerant Injection

The low temperature air source heat pumps using refrigerant injection technique can effectively solve the problems of high discharge temperature,system performance degradation and insufficient heating capacity in the traditional single-stage compression heat pump system in the cold seasons.The injection compressor is the key to the refrigerant injection technique.In order to improve the injection efficiency and the performance of the heat pump system,this paper conducts an in-depth study on the application of the injection rotary compressors in the small low temperature air source heat pumps.Firstly,based on the operating characteristics of the injection rotary compressor,the compression and injection process were theoretically analyzed,and the theoretical calculation model and CFD simulation model for the performance of the flash tank and internal heat exchanger cycle system using the injection rotary compressor were proposed.Secondly,the performance of internal heat exchanger cycle and flash tank cycle using an injection rotary compressor was tested and compared.The results of experiments showed that both the internal heat exchanger cycle and flash tank cycle can effectively improve the heating capacity and COP,and for the internal heat exchanger cycle,the injected refrigerant can be in a two-phase state,which is beneficial to reduce the discharge temperature of the compressor.Under the same injection pressure condition,when the injected refrigerant is in the vapor phase,the performance of internal heat exchanger cycle and flash tank cycle are equivalent;when the injected refrigerant of the internal heat exchanger cycle is in the two-phase state,the performance of the flash tank cycle is higher than the internal heat exchanger cycle.Then,the CFD simulation was carried out on the flow characteristics of the vapor injection rotary compressor,and the reliability of the CFD simulation results was verified by theoretical and experimental results.It is found that there are serious suction backflow and injection backflow during the operation process of the experimental compressor.According to the geometric structure and operating characteristics of the injection rotary compressor,the influence of different injection port positions on the suction and injection backflow of the injection compressor is discussed through CFD simulation.In addition,theoretical analysis and CFD simulation of the flow characteristics of the twophase injection rotary compressor were carried out.It is found that the injection quality of traditional internal heat exchanger cycle can not be controlled,and a novel internal heat exchanger cycle which can adjust the injection quality was proposed.Through the performance analysis of the novel internal heat exchanger cycle under different injection quality,it is found that this system can effectively solve the problem that the compressor discharge temperature is too high,so that the air source heat pump can run normally and efficiently under extreme environment temperature.Finally,by combining theory and CFD simulation,the structure of the injection port and the injection conditions of the system were optimized.The results show that the optimal start of injection rotation angle is 0°,and the optimal end of injection rotation angle is closely related to the maximum evaporation temperature when the injection path is opened.In addition,the injection pressure can be slightly higher than the pressure of the compression chamber at the end of the injection,which will only produce negligible injection backflow.And compared with the traditional heat pump system without injection path,the operating conditions of the heat pump system using the optimized injection rotary compressor can be extended down by about 10℃ while ensuring the heating capacity.The injection rotary compressor studied in this paper not only does not need to set a check valve in the injection path,but also can greatly improve the heating capacity and system performance of the heat pump under low temperature conditions,which is of great significance to the product design and promotion of low temperature air source heat pumps.