CFD Analysis on the Influence of Converging Duct Angle on the Steam Ejector Performance

Steam ejector is an essential part in refrigeration and air conditioning, desalination, petroleum refining, petrochemical and chemical industries. The ejectors form an integral part of distillation columns, condensers and other heat exchange processes. In this study, CFD (computational fluid dynamics) analysis based on the finite volume method was employed to investigate the influence of angle of converging duct on the ejector performance. The degree of angle of converging duct was varied at 0, 0.25, 0.5, 1.25, 2.0, and 2.75. The using of CFD method allowed not only the accurate prediction of the performance but also the identification of the shock/expansion wave, the circulation zone, and the pressure distribution of the axial direction. Verification with experimental data was also undertaken at various operational conditions. The comparisons of entrainment ratio between experimental and CFD results for various suction and discharge pressures at a fixed motive pressure show a good agreement. CFD studies show that the increase of converging angle affects on the increase of static pressure field inside of mixing duct. Hence, the length of shock train region is also influenced by the angle of converging duct. It is observed from this study that the entrainment ratio of ejector is influenced by the angle of converging duct. Ejector with degree of angle = 0.5 gives the highest value and then decrease with reference to the increase of converging angle. The flow visualization of stream functions inside the ejector shows that the flow separation phenomena and recirculation conditions occur in the ejector with larger converging angle. The optimum design of steam ejector is at converging duct angle of 0.5 degree which gives maximum entrainment ratio of 0.941