Numerical Simulation Of Two-Phase Wet Steam Flows Within Steam Ejector

Steam ejector refrigeration system has many advantages, such as simple structure, long service life, easy maintenance, security, and large suction capacity, also it can extract dust, corrosive gas. Now the society, energy-saving and environmental protection are increasingly advocated, as a core part of this system-Steam ejector, deserves to be further investigated. In the LAVAL nozzle and converging duct, there are the non-equilibrium wet steam flow attended by heat transfer process, phase-transition, so the flow mechanismis is more complex than the single-phase flow. However, most scholars only utilize the ideal gas model to simulate steam ejector as yet, could not clearly describe these complications and give good determination. In this study, numerical simulation method was adopted, with the help of ANSYS-FLUENT12.1package, vapor-liquid transition in high expansion flows, phenomenon of spontaneous condensation and effects on steam ejector performance were investigated.The main research studies contained in this paper are as follows:1. Mathematical model for the two-phase transonic flow of wet steam in the LAVAL nozzle is established, by the numerical simulation of its inward flow, the simulation results were validated with experimental data.2. Flow zones distribution in typical LAVAL nozzle, the condensation and compression choking wave were investigated firstly, and ways were explored to reduce condensation.3. The influence of operating conditions and geometry parameters changing on the spontaneous condensation in the LAVAL nozzle.4. By contrasting the experimental data with the simulation data under ideal gas and wet steam models, the differences were analyzed, the influence of the operating conditions and geometry parameters changing on two-phase flow of wet steam and performance of steam ejector were investigated from the flow structure changing point of view.The above study demonstrated that numerical simulation under the two-phase wet steam model clearly described the flow structure in steam ejector, steam loss produced by spontaneous condensation in the steam ejector does produce a certain impact on the performance, but the working pressure, back pressure, and the geometric parameters of the steam ejector play a decisive role. Therefore, in the case of rational design of these parameters, the additional degree of superheat can reduce the amount of condensation generated by the spontaneous expansion, and the adverse effects on the secondary steam.