Condensation in supersonic steam ejectors: comparison of theoretical and numerical models

Supersonic ejectors are commonly used for many applications in the field of refrigeration. In many cases, condensation or evaporation occur, either within the motive or suction flow. A very important case of condensing ejector is the steam ejector, which can be used for suction of non-condensable gases in steam power plants or in heat-powered chillers. Design techniques for ejectors are still a matter of discussion.Ideal gas models are usually employed to obtain a first set of dimensions. However, in the case of steam ejectors, the ideal gas behavior is far from being physically consistent. Other design techniques are based on interpolations of experimental data and, although empirical, can provide suitable sizing of the main ejector dimensions. Finally, a still higher level of modeling is multiphase CFD. Wet steam models are available in some commercial CFD codes and should be able to represent the non-equilibrium behavior of the flow. All these levels of analysis are surveyed and compared in this paper. CFD simulations are performed to validate a 1D design procedure and to investigate the effects of non-equilibrium condensation within highly supersonic stream of pure steam.