Simulation Of Pneumatic Conveying Of Charged Particle Flow In Pipe Based On CFD-DEM Method

In industrial production,pneumatic conveying,as a way of great economic efficiency,has been widely used in conveying of particle material.However,when particles are conveyed,they will be electrified and accumulate charges on their surfaces because of the particle-particle collisions and the contact between particles and the pipe wall,which may not only affect the pneumatic conveying efficiency,but also further cause safety accidents.However,the conveying conditions and particle charging on the conveying efficiency remains to be further studied.Therefore,in this thesis,the particle flow process in a pipe is simulated under different conveying conditions by coupling CFD-DEM method,in which the Mosaic model is used to calculate the charges carried by particles during transportation in a pipe,and further the conveying performance and efficiency under different conditions are investigated.First,CFD-DEM coupling modeling is established to simulate the particle flow in a pipe.The appropriate time-step and grid satisfying the computational accuracy are obtained on the basis of time independence and grid-independent verification.The effectiveness of the Mosaic model is verified by comparing the simulation results with the existing experimental results in the background of particle pneumatic conveying.Secondly,the effect of different conveying conditions on particle mass flow in pneumatic conveying is studied using the CFD-DEM method.It is found that the pipe inlet wind speed,pipe length,pipe diameter,and pipe inclination angle are key factors affecting the conveying efficiency of particle flow in pipe.When the pipe is vertical,the increase of wind speed will cause the particle charge increase,however,due to the limitations of the pipe length,the amount of particle charge will reach a maximum under a certain pipe length,at the same time making the particle mass flow reaches extremum.When the pipe diameter is as large as approximately 10 times the average particle size,the particle mass flow will not be affected by the pipe diameter.When the pipe is inclined,the particle mass flow peak will increase first and then decrease rapidly,while the inclination of horizontal peak platform increases gradually;with the increase of the inclination angle,the time that the particles flow through the pipe increases,so that the higher wind speed is needed to ensure that the particles are completely conveyed.While at the smaller wind speed,the particles may be stranded in the pipe further to cause blockage.Finally,by changing the pipe cross section size,the mass flow conveying performance and transport efficiency are studied when charged particles adhere to the pipe wall.By changing the cross-sectional size of the pipe,the relationship between the mass flow and the size of the cross-section is studied.The results show that,when the charged particles adhere to the pipe wall,the conveying particles show three different flow states,respectively,plugging,low and high efficiency flow.Improving the inlet wind speed can change flow state,and thus improve the conveying efficiency.At the same time,we can speculate that particle plugging is more likely to appear in the end of the pipe.