Numerical Investigation of the Effects of Steam Nucleation on the Steam Ejectors Performance

Abstract

Steam ejectors are widely used in different applications such as propulsion, refrigeration, evacuation and aerospace. The fundamental numerical approach in evaluating the characteristic parameters of steam ejectors was through considering steam as a single-phase gas. But, at some regions in steam ejectors, nucleation of steam is occurred. It is very important to evaluate the amount of wet steam at the first step. At the second step, it is vital to estimate the effect of steam condensation on the aerodynamics and thermodynamic performance of steam ejectors. In the present study, numerical simulation of a steam ejector at normal operation is undertaken. In the mathematical modeling of compressible flow within such equipments, wet-steam nucleation theory is employed to investigate the effects of wetness condition inside the ejectors. In order to verify the numerical simulation, wet steam results have been compared with a set of experimental data reported in previous literatures. By comparison of the numerical results with experimental data, it was concluded that steam condensation in the nozzle declines the maximum Mach number of supersonic flow which has a closer agreement with experimental reports. The numerical calculations were performed with a commercial code with a supplementary user-defined code and applied to a multi-block computational domain with structured elements. Some important items such as shock location, shock strength and pressure distribution along the centerline of the ejector were compared in the cases of wet and ideal steam simulations. Furthermore, the average compression ratio and entraining capability of the ejector were compared for both simulation methods. Moreover, the results show a strengthened shock wave under the assumption of wet steam which leads to an intensified pressure recovery inside the ejector.