| Steam ejector is a low grade vacuum pump which using high speed steam as working fluid to carry other gas. Because it can utilize low grade thermal energy from inexpensive or even free sources, and using water, the most environmental friendly substance, as its working fluid, its irreplaceable status has been focused by researchers for a long period. Especially in today’s increasingly energy-saving and environmental-protection society, carrying out further research about steam ejector is even more necessary. However, because of the relatively low entrainment ratio and the complicated nature of flow structure and mixing process within a steam ejector, traditional theoretical and experimental research methods could not clearly describe these complications and give good determination and limit the development of the steam ejector largely. In this study, numerical simulation method was adopted, with the help of ANSYS-FLUENT package, the influence of the operating conditions and geometry parameters changing on steam ejector performance was investigated from the flow structure changing point of view, which can maintain working stability and improve performance of steam ejector.The main research studies contained in this paper are as follows:1. Choosing suitable turbulence model and reasonable solve strategies to cope with flow structure in steam ejector under certain conditions, and the simulation results were validated with experimental data,so the foundation for the further study was laid firstly.2. After the accuracy of numerical simulation method was verified, the characteristics of the flow structure within steam ejector were analyzed and the key local flow structure such like shock-mixing layer, chocking position, and effective area, etc. were located, and then the relationship between these key flow structure and steam ejector performance was drawn out.3. Analysis concerning about the influences of operating conditions and geometry parameters changing on flow structure inside steam ejector was carried out respectively. 4. The effect of operating conditions and geometry parameters changing on steam ejector’s critical pressure was also analyzed.5. The research about spontaneously condensing in Laval nozzle was carried out which can lay a foundation for evaluating about the influence of spontaneously condensing wet-steam flow on steam ejector performance.The above study demonstrated that the shock-mixing layer plays a key role in dividing the flow region of primary fluid and secondary fluid and its shape provides effective methods for deeming working state and comparing performance of steam ejector; The changing of secondary fluid chocking status which include the chocking position and effective area turns into decisive factor for steam ejector performance; The spontaneously condensing phenomenon places evident effect on pressure, velocity and temperature of the flow in Laval nozzle and can reduce steam ejector performance.Therefore, through the research about flow structure within steam ejector can understand the internal mechanism of operating conditions and geometry parameters changing on steam ejector performance fundamentally, it also provide theoretical basis for maintaining stable working condition and performance improvement for steam ejector. |
