Effect Of Evaporative Supercooling On Ejector Transcritical CO₂ Heat Pump Cycle

CO₂ natural refrigerant has the characteristics of good environmental protection,high safety and excellent thermal physical properties.it is widely used in the field of heat pump water heater,because the heating process of the limited water flow can be satisfactorily satisfied under the transcritical cycle system.However,due to the large throttle loss,the transcritical cycle is faced with the problem of low operation performance,when using CO₂ refrigerant in the heat pump transcritical cycle system.Previous results show that using the supercooling cycle and internal heat exchanger can reduce the throttling loss and increase the system COP significantly in the transcritical CO₂ cycle system;An ejector is introduced into transcritical CO₂ cycle system to reduce throttle loss,and it is with the advantages of simple,reliable and economical.Based on the previous studies,this study proposes a new economic supercooling cycle.And effects of evaporative supercooling on transcritical CO₂ cycle and ejector transcritical CO₂ cycle are studied through thermodynamic theory analysis.Above all,according to the law of thermodynamics,an energetic model and an exergetic model are established for the evaporative subcooled transcritical CO₂ cycle system?ETCS?.And the calculation program is programmed by Matlab software,and the refrigerant parameters provided by Refprop software are invoked.And effects of evaporative supercooling on the COP and exergy efficiency of transcritical system is cleared.The research results show that under the outlet temperature of the gas cooler is40?and the evaporation temperature is 5?,the optimal temperature drop in the economizer is 14?in ETCS cycle.And by comparing the basic transcritical CO₂ cycle system.,the system COP,system exergy efficiency?_Ex,sx,s and unit volume refrigeration capacity increased by 24%,23.8%and 52%in ETCS cycle,respectively.Secondly,The constant-pressure mixing model?CPM?is adopted to study effects of evaporative supercooling on the COP,exergy efficiency and the characteristic parameters of ejector of the ejector transcritical CO₂ cycle system is analyzed.The research results show that under the outlet temperature of the gas cooler is 40?and the evaporation temperature is 5?,the optimal temperature drop in the economizer is 11?in EETCS cycle.And by comparing the basic ejector transcritical CO₂ cycle system,the system COP and system exergy efficiency?_Ex,sx,s increased by 24%,11.1%and 11.2%in the EETCS,respectively;With the increase of the temperature drop of T_wjj in the economizer,the lift pressure ratio R and the outlet dry degree x of the ejector are declining,while the ejector's ejection coefficient u and exergy efficiency?_Ex,ejex,eje are increasing.The results show that the subcooled cycle method proposed in this study can improve the operation performance of the system and reduce the irreversible loss of the system;And it has increased the ability of cooling and heating,and also improved the system COP.