The supersonic steam ejector is widely used in many industries which are steam powered such as oil, thermoelectric, refrigeration and so on. Many scholars analyzed the steam ejector by using ideal gas model and they ignored phase change, this may bring some errors for the flowing field of the ejector. In this study, the supersonic steam ejector was simulated using CFD (Computational Fluid Dynamics). Flowing field of the ejector was analyzed by using different state equations. The results shows that performance of the ejector was underestimated under the ideal gas model, and the entrainment ratio is 20%–40% lower than using real gas model. When phase changing was considered under real gas state equations, influences of working fluid pressure and back pressure were investigated. The results illustrates that working critical pressure and back flow critical pressure exist in the flow, and the entrainment ratio reaches its peak at working critical pressure. The performance of the ejector was almost the same when the outlet pressure was lower than critical back pressure. Effects of ejector geometries were also investigated in this paper. It shows that there are optimums of the relative position of the steam nozzle and the taper of the mixing section, length of mixing chamber and diameter of throat according to mass flow rate of second fluid. There are also critical length of diffuser and throat. Mass flow rate stayed the same when the length of diffuser or throat grows. This paper will provide a theoretical basis for ejector’s energy-saving and geometry optimization.

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