Numerical Simulation And Experimental Study On Performance Of CO₂Adjustable Ejector

The ejector has the advantages of simple geometric structure, low cost and no movingparts. It can increase the suction pressure of the compressor, therefore reduce the inputpower of the compressor and increase the coefficient of performance (COP) of therefrigeration system in the way which uses the ejector to recover the potential pressureenergy in the expansion process. In the paper, the experimental set-up of the trans-criticalCO2ejector refrigeration system was improved, and the adjustable ejector was developedon the basis of the previous theoretical and experimental studies on the performance of thefixed throat area ejector. The characteristics of the adjustable ejector with differentgeometry parameters were simulated using the CFD software in the desired workingcondition, and the experiments were performed for the trans-critical CO2adjustable ejectorrefrigeration system, it is of great significance to research on the system in theory andpractice.The performance of the traditional CO2two-phase refrigeration system with andwithout the internal heat exchanger (IHX) was measured, and the experimental results werecompared with these of the previous experimental studies under the desired workingconditions. The experimental results indicate that the performance of the new system wasimproved, the COP and cooling capacity of the trans-critical CO2refrigeration systemwithout IHX can be increased by28.15%and31.38%respectively, while the COP andcooling capacity of the system with IHX can be increased by27.01%and24.95%respectively.The experiments were performed for the trans-critical CO2adjustable ejectorrefrigeration system with and without IHX, and the influence of the pressure and outlettemperature of the gas cooler on the system performance was analyzed. The experimentalresults indicate that the COP and cooling capacity of the trans-critical CO2adjustableejector refrigeration system increase with the increase in the pressure of the gas cooler, anddecrease with the increase in the outlet temperature of the gas cooler. When the throatdiameter of the nozzle is about1.7mm, the COP and cooling capacity of the system is thehighest at the same working condition. The experimental results for the trans-critical CO2adjustable ejector refrigeration system indicate that the COP and cooling capacity of thesystem with IHX is higher than that of the system without IHX, the COP and coolingcapacity can be increased by10.33%and8.32%respectively. The COP and cooling capacityof the trans-critical CO2adjustable ejector refrigeration system is higher than that of thetraditional refrigeration system by7.08%and8.24%respectively.The internal flow in the CO2adjustable ejector with different geometry parameters under variable working conditions were simulated using the CFD software. When theprimary flow pressure increases, the shock position is close to the outlet of the nozzle. Theintensity of the shock wave decreases with the increase in the primary flow pressure, whilethe entrainment ratio increases. The simulation results indicate that under the desiredworking conditions the diameter of the nozzle throat affects the performance of the ejectorgreatly, the entrainment ratio increases with the decrease in the nozzle throat diameter.