Numerical Simulation And Experimental Study On The Performance Of Transcritial CO₂Two-phase Ejcctor

Nowadays, the two phase flow ejector has got more and more attention of peopleowe to its unique superiority. The two phase flow ejector used in the transcritical CO2refrigeration system can recover a part of the expansion work, and improve theperformance of the system. In this paper, the internal flow characteristics of the two phaseflow ejector were simulated numerically, the experimental study on the performance of thetwo phase flow ejector and the transcritical CO2refrigeration system were carried out, theperformance of the ejector and the transcritical CO2refrigeration system with differentgeometric size of ejectors under different working conditions were compared to find theaffecting factors both of the two phase flow ejector and the system. The effects of cross-sectional area of the first nozzle throat and working conditions on the performance of thedual-throat nozzle ejector and the transcritical CO2refrigeration system with dual-throatnozzle ejector were analyzed. The conclusions as follow:(1) Under the working condition of fixed gas cooler outlet pressure/temperature9.00MPa/43℃and evaporating temperature6℃, both the numerical simulation andexperimental results indicate that the performance of the dual-throat nozzle ejector firstlyincreases and then decreases with the increases in the cross-sectional throat area of the firstnozzle, the entrainment ratio of the dual-throat nozzle ejector achieves the maximum as theacross-sectional throat area of the first nozzle is1.54mm2.(2) The simulation results indicates that the entrainment ratio of the dual-throat nozzleejector increases with the increase in the gas cooler outlet temperature and decreases withthe increase in the evaporating temperature as the cross-sectional throat area of the firstnozzle is1.54mm2. Under the working condition of fixed gas cooler outletpressure/evaporating temperature9.00MPa/6℃, the entrainment ratio achieves themaximum as the condensing temperature is about43℃.(3) Under the working condition of fixed gas cooler outlet/evaporation temperature43℃/6℃, the entrainment ratio both the Laval nozzle ejector and the dual-throat nozzleejector firstly increase and then decrease with the increase in the gas cooler outlet pressure,and achieve the maximum value as the pressure8.50MPa and8.70MPa, respectively. Underthe working condition of fixed gas cooler outlet pressure/evaporating temperature8.50MPa/4℃, the entrainment ratio achieves the maximum value. The COP of dual-throatnozzle ejector refrigeration system decreases with the increase in gas cooler outlettemperature and pressure, and increases with the increase in evaporating temperature.(4) Comparing the dual-throat nozzle ejector refrigeration system and conventional system, under the working condition of fixed gas cooler outlet pressure/evaporatingtemperature9.00MPa/6℃, the COP ofthe dual-throat nozzle ejector refrigeration systemincreases by13.06%to the conventional system at most. As the gas cooler outlet pressure is8.50-9.20MPa, the COP of the dual-throat nozzle ejector refrigeration system is greater thanthat of conventional system, and the maximum increment of the system COP is about12.36%. The COP of the dual-throat nozzle ejector refrigeration system and conventionalsystem increase with the increase in the evaporating temperature, and the COP of dual-throat nozzle ejector refrigeration system increase by8.30%to the COP of the conventionalsystem at most.