Effect of vibration parameters and wall friction on the mixing characteristics of binary particles in a vertical vibrating container subject to cohesive forces

Abstract

The effect of particle cohesion, vibration parameters, and wall-particle friction conditions on the mixing process of binary spherical particles in a vertical vibrating container were studied by the discrete element method. The phenomena in the simulation can be explained by three mechanisms: void filling, convection, and self-organization. The results show that the mixing rate decreases with the increase of particle cohesion. Increasing the amplitude can increase the mixing rate, but the effect of improvement is no longer obvious when the amplitude exceeds a threshold. There is an optimal vibration frequency, and a higher or lower frequency will lead to the reduction of the mixing rate. The macro convection caused by the strong wall friction can promote the flow and disaggregation of particles, but also cause the segregation that large particles gather in the center of the convection unit and thus reduce the mixing index. The degree of segregation is approximately linearly related to the shear force difference from the sidewall to the center of the container. Cohesion changes the segregation by influencing this difference. Under proper conditions, the segregation increases first and then decreases with the increase of cohesion. The expected mixing degree can be obtained by selecting appropriate wall friction conditions and particle cohesion. • Mixing of binary particles depends on vibration parameters, wall friction and particle cohesion. • The strong wall friction effect leads to the convective segregation of particles. • The shear force difference has a linear negative correlation with the segregation. • There is an upper limit to the effect of promoting mixing by increasing amplitude. • There is an optimal value by changing frequency to promote mixing.