Study On Performance Of Adjustable Two-phase Ejector With Dual-serial-throat Nozzle

The use of the two-phase ejector in a traditional refrigeration system instead of the expansion valve can not only recover the potential energy of high pressure refrigerant, but also increase the suction pressure of the compressor, and the compression energy consumption is also reduced at the same time. In this paper, the effects of the geometric parameters and different working conditions on the performance of two-phase ejector with dual-serial-throat nozzle were investigated by using the computational fluid dynamics(CFD) technique, firstly. Secondly, a series of experiments were conducted to investigate the performance of the two-phase ejector refrigeration system with the different geometry of ejectors, including the divergence angle of the first nozzles, the cross-sectional area of the first and second throats, under the same working conditions. The effect of the condensing temperature and evaporation temperature was also experimentally investigated for a fixed geometric parameter of the ejector. Finally, the performance of the two-phase ejector refrigeration system and the conventional refrigeration system were compared under the same working conditions, and the experimental results were also compared with the simulation results. The conclusions are as follows:(1)Experimental results for the ejector with dual-serial-throat nozzle indicate that the entrainment ratio firstly decreases then increases with the decrease in the divergence angle of the first nozzle. As the divergence angle of the first nozzle is 3°,the secondary mass flow rate is maintained at its maximum value, and the entrainment ratio reaches to the maximum value. The simulation results indicate that the entrainment ratio is improved due to the decrease in the divergence angle of the first nozzle. The COP also exhibits a behavior of increasing with the increases in the cross-sectional area of the first throat.(2)The simulation and experimental results indicate that as the cross-sectional area of the second throat increases, the entrainment ratio is improved, and the entrainment ratio can reach to its maximum value when the diameter of the second throat is 1.9mm. The COP firstly increases then decreases with the increase in the cross-sectional area of the second throat.With a diameter of the second throat of 1.8mm, the COP value reaches its maximum value.(3)The experimental results show that as the condensing temperature decreases, the COP of the conventional and the two-phase ejector refrigeration system increase under a fixed geometric parameter of the ejector. The COP of the two-phase ejector refrigeration cycle becomes higher than that of the conventional refrigeration system by 3.4% with the condensing temperature in 43℃.The COP increases while the evaporation temperature increases.(4) The comparison between the simulation and the experiment results indicate that as the condensing temperature decreases, the entrainment ratio increases, and the entrainment ratio is improved when the increases in the evaporation temperature. The trend of the simulation results is agreed with the experimental results, but the simulation results are higher than the experimental results.(5) The experimental results indicate that as the divergence angel of the first throat is 3°, the diameter of the second throat is 1.8mm and the diameter of the first throat is 2.1 mm, the COP of the two-phase ejector system reaches the maximum value at the evaporation/condensing temperature of-1/50℃.(6)The comparison of simulation results by using 2D and 3D model show that the trend of simulation results is agreed with each other well. Compared with the experimental results, the simulation results have an unobvious difference, but the workload can be greatly reduced by using of a 2D model.