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

The expansion valve or capillary is replaced by a two-phase ejector to recover thepotential energy of the high pressure refrigerant and to increase the coefficient ofperformance in the two-phase ejector refrigeration cycle (TPERC). The previous researchresults showed that the key factor which affects the performance of the TPERC system isthe performance of two-phase ejector. So, the numerical simulation on the internal flowcharacteristics and the performance of the TPERC were carried out by using ANSYS CFXsoftware in this paper, and the experimental study on the performance of the TPERC werecarried out. The effects of the geometric parameters and working conditions on theperformance of the ejector were discussed, and the performance of the Laval nozzle ejectorwas compared with the two-throat nozzle ejector. Meanwhile, the performance of theTPERC system was experimentally investigated. The effects of the throat area and thediffuser angle of the nozzle on the performance of the ejector and the TPERC system wereanalyzed under the fixed working condition. The effects of the Laval nozzle andtwo-section nozzle on the performance of the vapor-liquid two-phase ejector werediscussed. The effects of the condensing temperature and evaporating temperature on theentrainment ratio of the ejector and the COP of the TPERC system were experimentallyanalyzed under the fixed geometric parameters of the ejector, and the experimental resultswere compared with the simulation results. The Conclusions are as follows:(1) Both the experimental and simulation results indicate that the entrainment ratioincreases with the increase in the cross-sectional area of the nozzle throat under a fixedworking condition. There is an optimal condensing temperature and evaporatingtemperature that make the entrainment ratio be maximized.(2) The simulation results indicate that the entrainment ratio firstly increases thendecreases with the increase in the divergence angle of the nozzle. The optimum divergenceangle of the nozzle that make the entrainment ratio be maximum is3°for the Laval nozzleejector while it is4°for the ejector with two-throat nozzle. The entrainment ratio of theejector with two-throat nozzle is a little more than that of the Laval nozzle ejector.(3) The experimental results indicate that the COP of the Laval nozzle ejector systemfirstly increases then decreases with the increase in the cross-sectional area of the nozzlethroat, which achieve maximum of2.85as the cross-section area of the nozzle throat is2.835mm~2. While the COP of the two-throat nozzle ejector system decreases with theincrease in the cross-sectional area of the nozzle throat. The COP of the two-throat nozzleejector system is higher than that of the Laval nozzle ejector system.(4) There is an optimal combination of the throat area of the first and second nozzles,and the divergence angle of the nozzle to maximize the entrainment ratio of the two-section nozzle ejector under a fixed working condition. The experimental results indicate that whenthe throat area of the first and second nozzles are3.464mm~2and2.269mm~2respectively,and the divergence angle of the nozzle is3°, the performance of the ejector and the systemcan be improved effectively.(5) Compared with the traditional refrigeration cycle, the COP of the Laval nozzleejector refrigeration system with the throat area of3.464mm~2is increased by1.2%and5.4%approximately under the working conditions of the evaporating/condensingtemperatures-1℃/50℃and1℃/55℃respectively, while the COP of the two-throat nozzleejector with the first throat area of3.464mm~2,second throat at area of2.269mm~2anddivergence angle of3degree is increased by1.1%and15%respectively under aboveworking conditions. The experimental results indicate that the TPERC system is moreadvantageous under the working conditions of lower evaporating temperature and highercondensing temperature.