| A R134 a liquid recirculating refrigeration system with ejector is proposed in this paper.The ejector is installed in front of the evaporator,and the liquid in the gas-liquid separator is entrained by the condensated high-pressure refrigerant,so as to realize liquid super-feeding of the evaporator without consuming additional energy,so as to improve the and cop refrigeration capacity of the system.Firstly,on the basis of the R134 a two-phase flow ejector refrigeration system,a special experimental sutup for the liquid recirculating system with ejector is established.The ejector is designed to be detachable for easy replacement and installation,so as to study the influence of different geometric sizes on ejection efficiency and system performance.The ethylene glycol aqueous solution is used as frozen water to meet the needs of lower evaporation temperature setting.Secondly,the inner flow in the ejector,which is the core part of the system,is numerically simulated.In this paper,CFD software was used to simulate and analyze the effects of throat equivalent diameter of ejector nozzle,length of mixing section and inlet temperature of ejector.The purpose is to obtain the fluid motion characteristics and detailed flow field distribution information and acquire the optimum structural parameters of the ejector.Finally,the influence of system operating conditions and the key structure parameters on ejector efficiency and performance of liquid recirculating refrigeration system is studied experimentally,mainly includes the evaporation temperature,condensation temperature,ejector throat equivalent diameter and ejector mixing section length,and the experimental results are compared with two-phase flow ejector refrigeration system.Through the analysis of the experimental results and simulation results,the following conclusions are obtained:(1)Compared with the two-phase flow ejection refrigeration system,the refrigeration capacity of the liquid recirculating refrigeration system has been greatly increased.Under different evaporation and condensation temperatures,the refrigeration capacity can be increased by 24.6%~45.9%.For most experimental conditions,COP of the liquid recirculating refrigeration system can be improved,up to 14%.For high condensation temperature(48 ?)and low evaporation temperature(-14 ?),COP of the liquid recirculating refrigeration system decreased.The entrainment ratio of the liquid recirculating refrigeration system is more affected by the pressure difference of the ejector,and has a greater improvement under the condition of large pressure difference.(2)The experimental results show that the refrigeration capacity and COP of the ejector liquid recirculating refrigeration system increase with the increase of evaporation temperature,and decrease with the increase of condensation temperature.The entrainment ratio decreases with the increase of evaporation temperature,and first increases and then decreases with the increase of condensation temperature,this is slightly different from the change in the entrainment ratio of the ejector in a two-phase flow ejector refrigeration system.(3)The experimental results show that with the increase of the throat equivalent diameter,the refrigeration capacity,COP of the liquid recirculating refrigeration system decrease,and the power consumption of the compressor slightly increased.Compared with the two-phase flow ejection refrigeration system,the trend of the entrainment ratio is different,the entrainment ratio of the liquid recirculating system decreases with the increase of throat equivalent diameter.(4)The experimental results show that the length of mixing chamber has great influence on refrigeration capacity,COP and entrainment ratio of the liquid recirculating refrigeration system.When the length of mixing section of 124 mm,the refrigeration capacity and COP of the system are greater than that of the system with mixing section of 112 mm,but the entrainment ratio is opposite.The maximum entrainment ratio of the ejector with 112 mm mixing section length can reach 1.26.Compared with the previous research,the entrainment ratio has been greatly improved.(5)The simulation results show that with the increase of the throat equivalent diameter,the position of the lowest fluid pressure at the nozzle is closer to the nozzle outlet,and the maximum velocity of the fluid is smaller.With the increase of the throat equivalent diameter,the entrainment ratio of the ejector decreases.The entrainment ratio is the largest as the throat equivalent diameter is 1.5mm.When the length of mixing chamber of 112 mm,the ejection effect is better than that of the system with mixing chamber of 124 mm,which is consistent with the experimental results.(6)Comparing the simulated results with the experimental results,it is found that both the experimental and simulated entrainment ratios decrease with the increase of the throat equivalent diameter.The throat equivalent diameter is 1.5 mm,the maximum values of both experimental and simulated entrainment ratios are obtained.The entrainment ratio of the simulated system is higher than that of the liquid recirculating system. |
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