A Study On The Performance Of Two-stage Compression Heat Pump/Refrigeration System Pressurized With A Two-phase Ejector

The air source heat pump can be cooled in summer or in winter to meet winter and summer needs.Moreover,it does not require coal,natural gas,etc.,and it will not pollute the environment.The use of an ejector instead of a throttle valve can restore the expansion work and effectively improve system performance.In this paper,the thermodynamic model of one-dimensional two-phase ejector is established by energy,momentum and mass conservation.The model is used to analyze the pressure lift and the entrainment ratio of different different pressure drops in the suction chamber.Optimum value of pressure drop exists making ejector performance optimal.A two-stage compression heat pump/refrigeration system pressurized with ejector is proposed,and the energy analysis model and excergy analysis model of the system are established respectively.Using R1234 yf as the refrigerant,the effects of intermediate temperature,evaporating temperature and condensing temperature on the performance of heat pump and refrigeration cycle system are studied under the design conditions and compared with the performance of a two-stage compression system under the same conditions.The results show that:(1)When the intermediate temperature rises,the COP and excergy efficiency of the heat pump system and the refrigeration system both increase first and then decrease,and there is an optimal intermediate temperature;the total excergy loss of the system decreases first and then increases,and the excergy loss is minimized at the optimal intermediate temperature.(2)When the evaporating temperature rises,the heat pump system COP and entrainment ratio also increase,the pressure lift of ejector decreases,and the total system loss and excergy efficiency decrease gradually.Both the refrigeration system COP and the pressure lift of ejector are increased,the entrainment ratio is reduced,and the total system exergy loss and the exergy efficiency are gradually reduced.(3)When the condensing temperature increases,the heat pump system COP and the entrainment ratio decrease,the pressure lift of ejector increases,the total excergy loss of the system gradually increases,the exergy efficiency gradually decreases.Both the refrigeration system COP and the pressure lift of ejector are reduced,the entrainment ratio is increased,the total system exergy loss is gradually increased,and the exergy efficiency is gradually reduced.(4)The system performance coefficient and excergy efficiency of the heat pump and refrigeration cycle are better than the two-stage compression system under the same working conditions.The performance improvement rate of the heat pump system can reach 13.9%,and the performance improvement rate of the refrigeration system can reach 10.63%.