Numerical Simulation And Analyses Of Adjustable Steam Ejector

Steam ejector is a device that allows high pressure steam and low pressure steam mixed to achieve moderate steam pressure and vacuum extraction. The main advantages of steam ejector are its good energy saving effect, simple structure, low cost, convenient repair, and no strict requirements for the pumping medium. Steam ejector is widely used in desalination, water, chemical, oil, air, etc.The structure of the conventional ejector is designed for the best performance in the given operation condition. Once the operating parameters deviate from the design condition, the performance of the ejector will decrease rapidly, even can not work. However, the adjustable steam ejector could maintain steady state by adjusting the throat diameter of nozzle, when the operation condition changes.The traditional theory and experiment methods can not make accurate analysis on the supersonic flow inside the adjustable steam ejector. This paper utilize the commercial simulation software STAR-CCM+ for three-dimensional numerical simulation to the adjustable steam ejector. The effects of operating and structure parameters on the internal flow field of adjustable steam ejector were investigated, and the relationship between the entrainment ratio, each part efficiency of the ejector, and mixing chamber vortex structure were analyzed.The main work:(1) Analysis the effects of back pressure, motive steam pressure, and secondary steam pressure on the internal flow structure and performance of the adjustable ejector;(2) Investigating the of influence of area ratio on the entrainment ratio, steam flow rate, nozzle efficiency, suction efficiency, mixing chamber efficiency and diffuser efficiency and other parameters;(3) Compared the simulation results between the adjustable and single nozzle steam ejector;(4) Analysis the vortex structure of the mixing fluids.The simulation results show that, the ejector can be operated at a relatively stable state by changing the area ratio under off design operating conditions. Operation pressure is a major parameter affecting the working performance of the ejector. The nozzle efficiency is only influenced by the steam pressure and the area ratio, which has no effect on the changes of the secondary steam pressure and secondary steam pressure. When the area ratio is a constant, there exists an optimal value of area ratio(Ar*) which maximum the entrainment ratio of the adjustable steam ejector for a given operating condition. Mixing chamber efficiency is the main factor affecting the ejector efficiency. Diffusion chamber efficiency increases with back pressure and area ratio increases, increases firstly then decreases with the increases of the working steam pressure, and decreases with the increases of the secondary steam pressure. The main factor that affects the mixed effect for the motive and secondary steam in the adjustable steam ejector is the stream-wise vortex. When the total vorticity is a constant, the higher stream-wise vortex strength, the higher mixing efficiency obtained. This study would provide reliable theoretical basis for the deep research in the theory of adjustable steam ejector.