Study On The Influence Of Throttling Pressure Drop On Performance Of Transcritical CO₂ Heat Pump System With Ejector

The proposal of the Kigali Amendment indicates that HFCs are being phased out.As one of the alternative refrigerants,CO₂ is extremely promising for heat pump applications due to its environmental-friendliness and excellent heat transfer performance.The introduction of an ejector is an effective means to reduce the throttling loss and improve the efficiency of a conventional transcritical CO₂ heat pump system.Different from the conventional CO₂ heat pump system,the throttling pressure drop in the CO₂ heat pump system with ejector is the difference between suction pressure and evaporation pressure,rather than the difference between condensation pressure and evaporation pressure,thus the effects on system performance may be quite different from that of conventional system.The study on the influence of throttling pressure drop on performance of CO₂ heat pump system with ejector under different operating conditions will contribute to the optimal control of the throttle valve and the improvement of the system performance,which has important significance for the production of CO₂ water heater with ejector.Therefore,the effects of throttling pressure drop on the performance of the transcritical CO₂ heat pump with ejector were theoretically and experimentally investigated under different external heat transfer conditions in this paper.The main contents are as follows:?1?A thermodynamic model of the transcritical CO₂ heat pump system with ejector was carried out.The throttling pressure drop was taken as an independent variable,and its influence on the system performance parameters such as heating capacity,heating coefficient and entrainment ratio was analyzed under different evaporator water flow rates,evaporator water inlet temperatures and gas cooler water flow rates,respectively.?2?The original experimental installation was reconstructed,and the experi-mental research that matched the theoretical research was carried out.The throttle valve was adjusted to change the throttling pressure drop,and the variation trends of the system performance parameters such as heating capacity,heating coefficient and entrainment ratio were studied experimentally under different evaporator water flow rates,evaporator water inlet temperatures and gas cooler water flow rates.?3?The theoretical and experimental results showed that under a certain external heat transfer condition,there existed an optimal throttling pressure drop that resulted in the optimal system performance.The system performance was improved by increasing evaporator water flow rates,gas cooler water flow rates and evaporator water inlet temperatures.Under different external heat transfer conditions,the optimal value of throttling pressure drop was different.Thus,optimizing the throttling pressure drop under different working conditions is helpful to improve the performance of the CO₂ heat pump system with ejector.