| Gas ejector is a device that uses high-pressure working gas to suck low-pressure gas.It is widely used in many fields,such as refrigeration system,vacuum system,ventilation system and fuel cell for its simple structure,no moving parts,easy maintenance and wide application range.Due to the shortcomings of traditional one dimensional design theory and single factor structural analysis based on experiment or numerical simulation method,this paper adopts genetic algorithm to optimize the multi-structure parameters of gas ejector,which can significantly improve the performance of gas ejector compared with the traditional method.In this paper,firstly,the gas injector is designed based on sokoloff's method,and then CFD software STAR-CCM+ is used for numerical modeling,and the model is verified.Then,the effects of the cross-sectional area ratio between the mixing chamber and the nozzle outlet,the nozzle spacing,the length to diameter ratio of the mixing chamber,the diffusion angle,the nozzle reducing-angle and the mixing chamber reducing-angle on the performance of the gas ejector are studied by using a single factor method.On this basis,through the orthogonal test compares the various structural parameters affect the size of the performance of gas ejector,select three structure parameters of greater influence as optimization variables.The relation expression is established between the three structure parameters and entrainment ratio by using the response surface method,using genetic algorithms for structural optimization;Finally,aiming at the optimal structure of gas ejector obtained by genetic algorithm,the influence of operating parameters and working gas types on its performance are studied.The results show that the entrainment ratio increases with the decrease of the mixing chamber's decreasing angle,and increases first and then decreases with the increase of the mixing chamber's cross-sectional area ratio,the nozzle spacing,mixing chamber's length-diameter ratio,nozzle's decreasing angle and diffusion angle.Under design conditions,the optimal levels of the structure parameters are as follows: mixing chamber and the nozzle exit section area ratio is 35;the nozzle spacing is 100 mm;mixing chamber's length to diameter ratio is 4;nozzle reducing-angle is 15° and mixing chamber reducing-angle is 15° and diffusion angle is 4°.When the gauge pressure of working gas increased from 0.4 atm to 0.7 atm(1atm is 101325 Pa),the best mixing chamber to the nozzle exit area ratio increases from 25 to 35.The optimum nozzle nozzle spacing increases from 0 to 100 mm.The best mixing chamber's length to diameter ratio increases from 3 to 5.The best nozzle reducing-angle increases from 10° to 15°.The best mixing chamber reducing-angle keeps into 15°.The best diffusion angle decreases from 5° to 3°.The entrainment ratio corresponding to the optimal structure obtained by genetic algorithm optimization is 12.638,which is 26.99% higher than the designed structure's entrainment ratio of 9.952.Through the analysis of the variable working conditions,it is found that the entrainment ratio increases with the increase of the working gas pressure,the increase of the suction gas pressure and the decrease of the outlet pressure.When the working gas pressure is lower than the critical value or the outlet pressure is higher than the critical value,the gas ejector cannot work normally.When different working gases sucks air,the smaller the molecular mass of the working gas is,the larger the entrainment ratio will be.The entrainment ratio is approximately proportional to the inverse of the arithmetic square root of the molecular mass of working gases. |
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