Investigation On The Performance Of R134a Refrigeration System Using An Ejector As An Expansion Device

The two-phase ejector has the advantages of simple structure, no moving parts, low cost, and low maintenance requirements. The use of two-phase ejector as an expansion device in refrigeration cycle can improve the system performance. So this is an ideal alternative which has research value and application prospect. Therefore, research on the performances of the two-phase ejector and the ejector refrigeration system is of significant importance.Firstly, the ANSYS CFX software was used in this paper to simulate the internal flow in the two-phase ejector, and the influences of geometric and flow parameters on the performance of the two-phase ejector were analyzed. Secondly, the experimental study was conducted to investigate the effects of the geometric parameters of the ejector, the working conditions of the system, the size of the auxiliary evaporator and the characteristics of the adjustable ejector on the performances of the two-phase ejector and the R134 a ejector refrigeration cycle. The conclusions are as follows:(1) The experimental results show that the smaller distance between nozzle exit position(NXP) and constant-area mixing section is of benefit to improve the performance of the two-phase ejector. As the NXP is 0 mm, both the entrainment ratio and the pressure lifting ratio of the ejector are maximum, the compressor power consumption is minimum,and the refrigeration capacity is maximum. So the performance of the system is the best. As the divergence angle of the first nozzle increases, the refrigeration capacity and coefficient of performance(COP) firstly increase then decrease, which achieve maximum values as the divergence angle of the first nozzle is 8°. So there is an optimal divergence angle of the first nozzle that makes the system to achieve optimal performance.(2) The simulated results indicate that as the primary flow inlet pressure increases, the entrainment ratio increases. So increasing the primary flow inlet pressure can improve the performance of the ejector. Under the fixed primary flow rate, the entrainment ratio decreases with the increase of the outlet pressure of the ejector. Moreover, the effect of the outlet pressure of the ejector on the entrainment ratio is significant for small primary flow rate. Besides, the outlet pressure of the ejector can not be too high, otherwise it will make the secondary flow rate decrease, and even lead to the entrainment ratio being 0.(3) The experimental results show that as the decrease of the evaporating temperature or the increase of the condensing temperature, the pressure difference between high pressure and low pressure in the ejector refrigeration system increases. So the ejector can recover more expansion work, and the pressure lifting ratio of the ejector increases.However, the compression energy saving is limited, and the refrigeration capacity decreasescontinuously with the decrease of the evaporating temperature or the increase of the condensing temperature, so the COP decreases.(4) The experimental results indicate that the ejector refrigeration system with the auxiliary evaporator may have the advantage only when the pressure drop of the auxiliary evaporator is less than the pressure lifting of the ejector. Otherwise, the performance of the ejector refrigeration system will be lower than the traditional vapor compression refrigeration system under the same working condition. Increasing the size of the auxiliary evaporator appropriately can reduce the pressure drop and improve the system performance.(5) The simulated and experimental results indicate that using adjustable ejector can change the primary flow rate. As the needle moves forward, the performances of the ejector and the refrigeration system firstly increase then decrease, which achieve maximum values as the effective area ratio of nozzle throat is 90%.