Numerical Simulation Of A R134a Two-phase Ejector And Experimental Study On The Performance Of System

The expansion valve or capillary is replaced by a two-phase ejector to recover the potential energy of the high pressure refrigerant and to increase the coefficient of performance(COP)in the two-phase ejector refrigeration cycle(TPERS).The previous research results showed that the key factor which affects the performance of the system is the performance of the two-phase ejector.In this paper,the numerical simulation and experimental study on the internal flow characteristics and the performance of the two-phase ejector refrigeration cycle were carried out.The effects of the geometric parameters and working conditions on the performance of the vapor-liquid two-phase ejector were discussed.It is of great significance to improve the performance of the two-phase ejector refrigeration cycle.In this paper,the internal flow characteristics of the ejectors with different geometric parameters were simulated using the CFD software.Under a fixed working condition,the effects of the geometric parameters on the performance of the vapor-liquid two-phase ejector were analyzed.And the effects of the working conditions on the performance of the vapor-liquid two-phase ejector were analyzed,using a ejector with fixed geometric parameters.The performance of the two-phase ejector refrigeration system with refrigerant R134a as working fluid was experimentally investigated.Under a fixed working condition,the optimal combinations of the nozzle throat diameter and the mixing chamber diameter were discussed.Meanwhile,the effects of the evaporation temperature and condensation temperature on the performance of the ejector and the TPERS were experimentally investigated and the results were compared with the numerical simulation results.The Conclusions are as follows:(1)The experimental results indicate that there is an optimal combination of the nozzle throat diameter and the mixing chamber diameter to maximize the entrainment ratio under a fixed working condition.The entrainment ratio of the ejector with the throat diameter of 1.4mm and the mixing chamber diameter of 13mm reaches to the maximum value,under the conditions of-1℃ evaporating temperature and 55℃ condensing temperature.This result is consistent with the experimental result.The entrainment ratio of the ejector reaches to the maximum value while the mixing length is 8 times of the mixing chamber diameter,using the ejectors with dcr=1.4mm、D3=1 3mm or dcr=2.0mm、D3=16mm.(2)The simulation results of the R134a two-phase ejector under different working conditions show that the entrainment ratio of the ejector decrease with the increase in the discharge pressure of the ejector,and drop firstly than increase with the increase in the undercooling degree.The superheat degree has little effect on the entrainment ratio.(3)When the throat diameter and the mixing chamber diameter of the ejector is 2.0mm and 16mm respectively,the optimal evaporating temperature is 3℃ under the condition of 55℃condensing temperature to maximize the entrainment ratio.And the optimal condensing temperature is 50℃ under the condition of-1℃ evaporating temperature.(4)The ejector with the throat diameter of 1.7mm and the mixing chamber diameter of 13mm was used in the TPERS.Compared with the traditional refrigeration cycle,the COP of TPERS is increased by 20%approximately under the working conditions of the evaporating temperature 7℃ and the condensing temperature 55℃.The COP of the TPERS is not improved under the other working conditions,which is caused by the low mass flow in the TPERS.