The effect of rotational speed on granular dynamics and homogenization in a vertical bladed mixer

Abstract

Mixing of granular materials is very widespread operation used in many industrial applications. Nevertheless, at present time the descriptions of homogenization mechanisms are still not well explained. Therefore, in this work the mixing process of approximately 42,000 spherical beads differed only by their colors was studied in a vertical mixer with two opposed flat blades with 45° rake angle by using Discrete Element Method (DEM). Generally, it is known for liquids that rotational flow can be divided into two types: primary and secondary motions. Homogenization is especially caused by secondary flow. In case of granular mixing, the situation is not so simple. Even though many investigations deal with the influence of secondary flow in liquids, knowledge about existence of the granular secondary motion is almost negligible. In this work, the methodology for granular secondary flow detection is proposed by averaging radial and axial velocity fields in tangential direction. The main aim of this work is the description of influence of primary and secondary flows on the homogenization process. It has turned out that tangential velocity has significant effect on the homogenization of side-by-side configuration and secondary flow influences especially effectiveness of mixing process for bottom-up initial packing.