Theoretical Study And Numerical Simulation Of Vacuum Generator In Pneumatic Conveying

The vacuum generator is applied in the cleaning process of pneumatic conveying system,which can increase the air flow by introducing the external air without extra compressed air.This paper puts forward the application of the vacuum generator in the pipeline cleaning system,and designs the flow chart of the application of vacuum generator in the pipeline cleaning process of pneumatic conveying system.Based on CokoIIoB's theory,the optimal injection coefficient,geometry parameters and critical back pressure of vacuum generator were programmed using python software,which solves the problems such as repeatedly iteration,table look-up and interpolation.The numerical simulation method was used to verify the theoretical calculations.Through the verification of 15 vacuum generators,the maximum error value between the theoretical calculation and the simulation values of the optimal injection coefficients is18.79%,which indicates that the values based on the theory is highly reliable.Using numerical simulation methods,this paper also discusses the influence of different working conditions and different geometric parameters on the performance of the vacuum generator.Through the simulation of 16 different working conditions,which founds there is only one working condition that makes the vacuum generator happens to be in the limit state.At this time,increasing the working pressure or reducing the outlet back pressure will keep the vacuum generator under the limit state,but if reducing the working pressure or increasing the back pressure,the vacuum generator will be out of the limit state,and the injection coefficient and critical back pressure will rapidly decrease.Based on the simulation of vacuum generator with 5 different mixing chamber diameters and 9 different nozzle distances under different compression ratios,it is concluded that the diameter of the mixing chamber of the vacuum generator designedaccording to Coko?oB's theory is the optimal value,but the throat distance deviates from the optimal value,and the optimal value of the throat distance should be equal to the size of the nozzle throat diameter.The injection coefficient is influenced by the the diameter of the mixing chamber and the throat distance.The pressurization capacity of the vacuum generator is mainly affected by the diameter of the mixing chamber.In order to expand the adaptable operating range of the vacuum generator,two regulation ways which included nozzle throat adjustment and working pressure adjustment are discussed in this paper.The nozzle throat diameter or required working pressure can be calculated according to the variable outlet back pressure while the outlet air flow keeping constant.