Numerical study of the mixing efficiency of a ribbon mixer using the discrete element method

Abstract

We describe a simulation of granular flow in an industrial ribbon mixer. Such simulations are important to analyze mixing efficiency but they have not been conducted previously in a ribbon mixer, owing to complex boundary conditions. The simulations in this study use the discrete element method (DEM) with a wall boundary model based on a signed distance function (SDF). Introduction of the SDF allows for an accurate representation of the boundary, which is important for proper analysis of granular flow in the ribbon mixer. The adequacy of the DEM/SDF approach was validated qualitatively and quantitatively. The degree of mixing in the ribbon mixer was evaluated using a binary mixture mixing index. The effects of the amount of powder, blade speed and initial loading on the degree of mixing were investigated numerically. In the ribbon mixer, the change of mixing state in the axial direction was found to be much smaller than in the perpendicular direction and an increase in the amount of powder and the blade speed generate better mixing. Only the initial loading and amount of powder were found to be critical for good mixing in the ribbon mixer. The mixing mechanism was investigated by DEM/SDF and an optimal initial loading and amount of powder were suggested for better solid mixing.