The Mathematical Modeling And Structure Optimization For A Steam Ejector

With the continuous improvement of energy-saving requirements, the problem of exhausted steam recovery have caused more and more attention, therefore, it is necessary to research deeply on the technology of steam exhaust recovery. Steam ejector is a kind of equipment, which can improve the pressure of low-pressure fluids, but does not need to consume the mechanical energy. Energy-saving effect is remarkable. The paper is mainly aimed at researching the working performance, when the steam ejector recycles a low-pressure exhaust steam. Although the structure of ejector is very simple, but its internal flow field is very complicated. It exists shock waves, viscous interference, gas effect, and so on. If only using the semi-empirical and semi-theoretical method to design calculation, it will take large error.In order to reduce the design error, based on the semi-empirical and semi-theoretical method the subject firstly initially builds a physical model of the steam ejector under the special working condition, and then it uses CFD technology to perform numerical optimization and analyze its internal flow field in detail. By continuously adjusting the each part structure parameters of the model, the paper analyzes how the geometric dimensioning of the model influents its work performance, and then optimizes its the structure size. At last, we can get the optimal structure of the steam ejector under the design working conditions. The research shows that improving structure size of the model can effectively increase the injection coefficient and improve its work performance.In order to test the adaptability of the optimized model on the variable condition, the paper studies the variable condition property, when the three working parameters of working pressure, ejection pressure and outlet pressure change in a single factor. The research shows that if the working steam pressure is too high or too low, it will be detrimental to the normal operation of ejector. Under a certain working steam pressure, the ejection coefficient of steam ejector increases gradually with the increase of steam pressure, but if it exceeds the critical value, the working performance of ejector will be decreased with the increase of steam pressure. For the model the appropriate scope of the working steam pressure is:0.9MPa～1.1MPa, and when the working steam pressure is0.9MPa, the ejection coefficient is the largest, the model achieve its optimal performance; the injection coefficient of the steam injector increases with the injection pressure increasing, but in actual engineering, the pressure of steam exhaust is generally very low, and is determined by the scene, therefore we generally do not consider raising the steam exhaust pressure to improve the performance of the equipment; The steam ejector can only run efficiently in the back pressure within a certain range, and within the scope of critical pressure for change, the ejection coefficient is almost the same. If it is more than the critical pressure, the ejection coefficient will decrease rapidly. For the model, the critical back-pressure is about0.4MPa.