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

In this study the simulations of granular flow in a batch mixer with independent double axial mixing are presented. The simulated granular flows were used to analyze the mixing efficiency. Such analysis has not been conducted previously for such a batch mixer, because of the complex mixing conditions. The simulations performed 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 batch mixer. The adequacy of the DEM/SDF approach was validated quantitatively in experiments. The degree of mixing in the batch mixer was evaluated using a mixing index of a binary mixture. The effects of the powder amount, blade speed, initial loading patterns and secondary mixing on the degree of mixing were investigated numerically. In the batch mixer considered in this work, the change in mixing state in the axial direction was found to be much smaller than that in the perpendicular direction. The increase in the mixing speed not only reduces mixing time but also substantially increases the mixing performance if measured per number of rotations. However, the increase in the powder amount reduces the mixing performance. The additional secondary mixing affects the axial-mixing performance. However, the overall mixing performance does not change. In addition, neither the mixing axis position nor the mixing speed appreciably affects the mixing performance. All the mixing differences can be associated with the differences in the granular behavior, irrespective of different speeds, powder amounts or mixing setups. (C) 2016 Elsevier B.V. All rights reserved.