Variable Structure Performance Analysis Of Adjustable Ejector

The steam ejector is a pressurized,vacuum and mixing device that uses high pressure steam to pump low pressure steam for energy and mass exchange between fluids.The ejector has the advantages of simple structure,simple manufacture and remarkable energy saving effect,and is widely used in the fields of petrochemical,industrial refrigeration,fuel cell,aerospace and desalination.Due to the complexity of the fluid mixing process inside the injector,there are jet,entrainment,shock and shear layers.The flow field characteristics change significantly when the working conditions change,resulting in poor adaptability of the injector to working conditions.Therefore,the structural optimization and performance analysis of steam ejectors have important engineering significance.The traditional ejector is mostly fixed structure,and it has good performance only under fixed working conditions.When the working condition changes,its working performance will be reduced.Therefore,the research on adjustable ejectors has become an important research direction.In this paper,the ANSYS software is used to calculate the fixed and adjustable ejectors,and the internal flow field is observed and analyzed.The effects of pressure of primary fluid,pressure of suction fluid and discharge pressure on the ejection performance are obtained,and the structure of the ejector is optimized.The effects of nozzle distance,adjustment cone on the throat area and the contraction angle of the mixing chamber on the ejection performance were studied.The optimal nozzle distance and the optimal mixing chamber contraction angle were obtained.The main research contents and conclusions of this paper are as follows:1.One of steam ejectors used in the experiment was selected as calculation model,based on the grid independence verification,the simulation results of the entrainment ratio show a good agreement with the experimental data.By analyzing the influence of discharge pressure on the injection performance,three working modes of the ejector are obtained:critical mode,subcritical mode and reflow modet.2.When the structure of the fixed ejector was determined,the effects of pressure of primary stream on the injection performance,critical back pressure and suction pressure were studied.It is found that there is a best value for pressure of primary fluid to maximize the injection coefficient;the larger the working pressure,the larger the critical back pressure,and the smaller the design point of the suction pressure.3.The effect of the nozzle exit position was analyzed.It is found that there is an optimum nozzle distance to maximize the entrainment ratio;and as the nozzle distanceincreases,the optimal pressure of primary fluid becomes smaller,the critical back pressure becomes larger,and the working range of the ejector becomes wider.4.The effect of the adjustable ejector was analyzed,it is found that the larger the adjustment cone accounts for the throat area the larger the entrainment ratio,the larger the optimal pressure of primary of fluid,and the smaller the critical back pressure,the narrower the range in which the ejector can work.The adjustment cone accounts for the throat area also affects the shock intensity and the optimum nozzle distance.5.The effect of the contraction angle of the mixing chamber was studied,it is found that there is an optimal mixing chamber contraction angle,which maximizes the entrainment ratio.The percentage of the adjustment cone to the throat area affects the rate of change of the entrainment ratio with the contraction angle,but does not affect the optimal mixing chamber contraction angle.