Discrete element analysis of the particle mixing performance in a ribbon mixer with a double U-shaped vessel

In this study, a discrete element method is employed to simulate the mixing process of solid particles in a horizontal ribbon mixer with a double U-shaped vessel. A mixing index, i.e. the so-called Lacey index, is adopted to evaluate the mixing quality of particles. The effects of the operational and geometrical parameters including initial loading, particle size, impeller rotational speed, and inner blades on the mixing quality of particles have been investigated. Results suggest that the initial loading and the impeller rotational speed have significant effects on the mixing quality of particles, while the other two parameters have relatively small effects. Moreover, the effect of each parameter on the mixing quality has been explained by utilizing the relative velocity components between the centroids of particles after collision, and this ribbon mixer provides much more intense relative movements of particles along the vertical direction than the axial and side-side directions. Finally, the mixing performance between the ribbon mixers with respective single and double U-shaped vessels is compared. Results show that the ribbon mixer with a double U-shaped vessel shows better mixing performance under top-bottom and front-back initial loadings, however, worse mixing performance under side-side initial loading.