Optimization Of Steam Ejector Nozzle Structure And Operating Parameter

Steam ejector is a fluid machine that uses high-speed steam jets to carry working fluid.It has the obvious advantages of simple structure,no moving parts,easy maintenance,and wide working medium.In the fields of refrigeration and seawater desalination,but the shortcomings of the steam ejector are low,and the practical application requires a large amount of land,which limits the wider application of the steam ejector.In recent years,as the current world is plagued by the energy crisis,steam ejectors have become more and more important as an environmental protection device,and researchers have entered a new stage in their research on ejectors.In recent decades,with the development of computer technology,scholars have become possible to optimize the internal flow field structure of the ejector and the ejection characteristics of the ejector.The internal flow process of the ejector is complicated,and there are shock waves,boundary layers,congestion and other phenomena.The current mixing mechanism is not clear.The influence of the nozzle on the performance of the ejector is critical.The computational model,through computational fluid dynamics methods,numerically simulates the effect of different nozzle structures and different operating parameters on the ejector exhaust performance.The main contents of this article include:1.In order to verify the accuracy of the simulation results,the wall pressure distribution of the laboratory’s jet refrigeration system is compared with the simulated wall pressure distribution map.The comparison results show that the simulation results are in good agreement with the experimental measured data.The reliability of the simulation results.2.The performance of the ejector under different nozzle structures is studied.The effects of nozzles with different throat diameters,different exit positions,different tapered sections,and gradually expanded sections on the internal flow field structure and performance of the ejector were studied.It was found that when the ratio of the nozzle throat diameter to the ejector diameter was 0.08 At this time,the ejection coefficient of the ejector reaches the highest.Too large or too small nozzle throat diameter will reduce the ejection coefficient.At the same time,the separation of the boundary layer will occur.However,the location of the separation is different,and the optimal nozzle exit The position makes the ejection coefficient of the ejector the highest,and the angle of the tapered section has no effect on the performance of the ejector,but it needs to be greater than 0 degrees,and the angle of the tapered section must be greater than or equal to 6 degrees.3.The effect of different operating parameters on the performance of the ejector was studied.The flow field structure and ejection coefficient of the ejector under different working steam pressure,ejection steam pressure,and outlet back pressure were studied.The research results show that the ejection coefficient first changes and then decreases sharply as the back pressure increases.In the critical mode of the ejector,when the back pressure is increased,the shock wave position at the throat exit will move upwards,and the phenomenon of the mixing chamber remains unchanged and continues Increase the back pressure.In the subcritical mode,the working condition in the mixing chamber is broken,and severe separation of the boundary layer occurs.As the working steam pressure increases,the ejection coefficient first increases and then decreases,and the jet core volume will always increase;Increasing the injection steam pressure will lead to an increase in the ejection coefficient.The relationship between the two is a proportional function and the increase of the injection steam can improve the anti-backpressure capability of the ejector.4.The nozzle throat diameter that has the most impact on the performance of the ejector is studied.It is found that the larger the nozzle throat diameter is,the stronger the anti-backpressure capability of the ejector is,but the lower the highest ejection coefficient is,the higher the maximum back pressure that the ejector can work If the working steam pressure changes,the ejection coefficient of the ejectors with different throat diameters will always reach the optimal value as the working steam pressure increases.The working steam mass flow that reaches the optimal value is a fixed value;the smaller the nozzle throat diameter,the The faster the injection coefficient increases with the ejection steam pressure.In this paper,through the comprehensive analysis of different nozzle structure parameters and operation parameters,and through the comprehensive analysis of the flow situation inside the injector(jet core phenomenon,shock wave phenomenon,boundary layer separation phenomenon),we can provide help for the structural design and operation parameters design of the injector.