| The vacuum generator is used in the pneumatic industry in the vacuum transportation process,which can quickly generate negative pressure and achieve short-distance negative pressure transportation.This paper combines the application of the vacuum generator in modern industry,and uses numerical simulation methods to discuss the including vacuum generation.The effect of structural factors and external factors on the degree of vacuum and pumping speed.This article first performed a simulation analysis on the Rafael nozzle separately.From the simulation results of the internal flow field of the Rafael nozzle being pulled down under different structures and conditions,(1)the area ratio of the Rafael nozzle(the exit section of the nozzle)And nozzle throat section)The value is uniquely determined by the Mach number of the nozzle outlet gas,that is,if a certain Mach number of fluid is to be obtained at the outlet of the Lafar tube,then the nozzle area ratio that can be achieved at this speed is the only fixed of.(2)The outlet fluid speed gradually increases with the increase of the intake pressure or the decrease of the outlet back pressure.After reaching the critical value,the constraint of the nozzle area ratio gradually stabilizes.(3)When the area ratio is determined,different exit expansion angles have less influence on the nozzle exit speed.Therefore,there is greater flexibility in the selection of the expansion angle in actual production.Based on Sokolov's theory,this paper calculated the theoretical values of the geometric parameters of the vacuum generator,and verified the results of the theoretical calculations by numerical simulation methods.The vacuum generators of different working conditions and different structures were separately analyzed.The simulation analysis explored the effect of 10 operating conditions on vacuum degree under different inlet pressures and different outlet back pressures.Through a comparative analysis of these 10 operating conditions,it is concluded that there is a critical operating conditionsuch that the maximum vacuum degree of the vacuum generator is exactly the maximum value in the limit state,and the maximum vacuum degree at this time is 80 kPa.If you continue to increase the inlet pressure or decrease the outlet back pressure,the vacuum will not continue to increase.However,if the intake pressure is reduced or the outlet pressure is increased before the critical point,the vacuum degree will decrease sharply,and the vacuum generator will leave the limit state.Then,under the same working conditions,the vacuum generators of 5 different mixing chamber diameters and 5different nozzle area ratios(ratio of the outlet area of the Lafar tube to the throat area)were simulated and analyzed.The maximum vacuum degree follows The nozzle area ratio increases with the increase.The larger the area ratio,the greater the maximum vacuum that can be achieved,but the growth rate is slower.The area is relatively small,and the upper limit of the vacuum degree reached is low,but the growth rate is fast,so a relatively high vacuum degree can be achieved at a lower intake pressure.In a certain range,the degree of vacuum increases with the increase of the diameter of the mixing chamber,but decreases with the increase of the diameter of the mixing chamber after reaching the maximum value.Therefore,there is an optimal mixing chamber diameter.The simulation result is between 28mm-30 mm.The difference between the diameter of the mixing chamber of the vacuum generator designed according to Sokolov's theory is within 10%.The outlet back pressure has a greater impact on the degree of vacuum.As the outlet back pressure increases,the pressure in the mixing chamber increases and continues to affect the vacuum chamber.When the back pressure reaches 100 kPa,the vacuum generator returns,a part of the working gas flows out from the ejection outlet,a positive pressure appears in the vacuum chamber,and the vacuum generator fails. |
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