Numerical Simulation And Stirring Characteristics Of Powder Mechanical Stirring Process

As a typical unit operation,stirring is widely used in chemical,food,biological,pharmaceutical and other industries.Because of the complexity of mixing process,there is no accurate and reliable power calculation formula for powder mixing equipment.In practical engineering application,the determination of mixing power is generally estimated by experience,which has a large error.When the power of the motor selected is not suitable,the production cost increases and the power factor reduces during operation.Therefore,with the aim of estimate the mixing power accurately,moreover to provide a theoretical guidance for practical engineering applications,the numerical simulation and experimental verification are employed in this paper.The effect of characteristic parameters and powder mixing process on the mixing power are investigated in this research.Finally,the power calculation formula is obtained by fitting.In addition,the stress and strain of the impeller are analyzed by DEM-FEM co simulation method,and the optimization method is proposed for the severe deformation.The main research contents and results are as follows:（1）It is found that the particle is in the state of tangential motion,and the particle is in the state of upward motion.The combined velocity and tangential velocity of particles at the tip of impeller in powder mixer are higher than those in other areas,while the minimum combined velocity is in the center of bed bottom and the minimum tangential velocity is in the center of mixing drum.The vertical velocity of particles in each region is close,and the vertical velocity near the wall is slightly higher than that in other regions.（2）Numerical simulation and power test are used to study the influence of specific powder mixer parameters on power consumption and torque.The results show that power consumption P in powder mixer is positively correlated with speed n,impeller diameter d,inner diameter D,powder densityρand blade number n.When the impeller diameter changes only,P=0.68N³（d/D）^3.81D⁵ρ,R²=0.993;when the impeller number changes only,P=0.51N³ρ^2/3n^2.27,R²=0.99;considering the above factors,it is concluded that P=2.23N³（d/D）^2.51D⁵ρn^0.56,R²=0.95.（3）The mixing process is similar to the simulation,and the simulated particle distribution is in good agreement with the experimental results.The torque speed relationship and the power speed relationship are similar to the simulation,and the simulation results are in good agreement with the test results.The deviation between the experimental value and the calculated value is less than 10%,which indicates that the derived power calculation formula is reliable.（4）The influence of particle characteristics on stirring power and torque is studied.The results show that when the filling amount of particles is the same,the torque value and power value increase with the decrease of particle size at the same rotating speed;no matter what particle size,the power value increases linearly with the increase of rotating speed;under the same particle size scale,the influence of particle distribution mode on torque is relatively small;the phase change is obvious At the same packing height,except for spherical particles,the torque and power values of particles with other shapes decrease with the decrease of sphericity.（5）The results of DEM-FEM co simulation show that the stress at the tip of the impeller is the largest,and it is seriously deformed by particle impact,and its stress value is significantly higher than that in the center of the impeller.The simulation results show that the optimization method is reliable,and the optimized impeller reduces the overall stress and strain,which can improve the stability of the powder mixer.