| Liquid-gas ejector is a fluid machinery and mix reaction equipment which is used to transfer energy and quality. It is reliable, convenient for installation and maintenance,good sealing, and make for transporting toxic, explosive, flammable and radioactive medium. All kinds of energy can direct to be the work force of jet pump and don’t need to add other ancillary equipment. So the jet pump has integrated high-value application.but the structure of jet pump is rather special, it has large energy loss during the fluid mixing process, so that the jet pump efficiency is low, to some extent, it limits the application range of jet pump.In this study, numerical simulation method was adopted, with the help of FLUENT 14.0 package, the influence of nozzles structure and geometry parameters changing on ejector performance was investigated from the flow structure changing point of view, which can maintain working stability and improve gas sucking ability of liquid-gas ejector.The main research studies contained in this thesis are as follows:1. Choosing suitable turbulence model,multi-phase model and reasonable solve strategies to cope with flow s tructure in liquid-gas ejector under certain conditions, and the simulation results were validated with experimental data.2. Conducting numerical simulation by changing two important parameters of jet pump which is the distance between throat and nozzle, area ratio. It is found that ejector’s gas absorbing ability achieve the best when NXP value reaches 1.5 times the diameter of the nozzle and area ratio vary range within the range from 4 to 73. Using numerical simulation method,to plot the flow structure and two phase liquid-gas mixing rulesinternalthe single nozzle ejector, then change structural form of nozzle, that is changing convergent nozzleto the orifice nozzle, to stuy the ejector external gas-sucking characteristics,and internal flow mechanism..4. Acquire simulation result of multi-nozzle ejector,compare performance differences and internalflow characteristic between the single nozzle and multi-nozzle ejector. It is illustrated that flow field structure internal jet pump is closely related with the structure and number of the nozzle.Effect of spraying of four nozzle is better than that of single nozzle, high speed liquid jet from four small nozzle, will immediately be scattered, dispersed into small droplets and is uniformly mixed with the surrounding gas, and in the middle of the throat the process of mixing has been completed. In contrast, it takes a long distance before the high speed jet core disappear when the jet is sprayed from the single orifice nozzle before thevelocity difference between two phase is still larger before reach the exit.5. Comparing gas sucking capacity between the 4 nozzle,5nozzle and 9 nozzle to explore the internal cause resulting in external variation of suction gas capacity. It is indicated that the number and arrangement of nozzle is a very important aspect of of jet pump, compared with the other two cases,9 nozzles caes is provided with has better performance of gas sucking.This study above demonstrated that distance frome nozzle to throat,area ratio of nozzle and throat are two important parameters affecting the external performance of ejector, where exists an optimal value making the suction gas efficiency achieve the best. The number and distribution of nozzles change the flow pattern and the mixed behavior of two phase within the ejector causing the performance of gas-sucking varies widely.T Under the condition of the same area rate of two type 9 nozzle ejector, parallel and focusing arrangement of nozzle causes distribution of the pressure field, velocity field and temperature field inside the ejector differently.Therefore, through the numerical simulation research about flow structure within liquid-gas ejector can understand the internal mechanism of nozzle structure and geometry parameters changing on steam ejector performance fundamentally, it also provide theoretical basis for design optimization and performance improvement for steam ejector. |
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