Solids motion and segregation of binary mixtures in a rotating drum mixer

Mathematical modelling based on the continuum assumption and the dense phase kinetic theory is used in the work. It is found that the model captures the main features of solids motion and segregation in the drum and the results agree well with limited experimental data. The results show a clear two-region bed structure in the transverse plane of the drum operated in the rolling mode in terms of both total solids concentration and solids velocity distributions, a surface (active) layer with a low average concentration and a high velocity, and a passive layer close to the drum wall with high solids concentration and low solids velocity. The thickness of the two regions in terms of solids concentration differs greatly from that in terms of solids velocity, suggesting inaccuracy of the thin layer approximation models proposed in the past for predicting solids motion in the surface layer of rotating drums operated in the rolling mode. The results also show a clear core-shell structure in the transverse plane of the drum in terms of concentration of small and large particles. Under the conditions of this work, small particles tend to concentrate in the core region, while large particles tend to occupy the shell region, consistent with most experimental observations. Starting with a homogenous mixture of small and large particles, the above mentioned bed structures are found to be nearly fully developed within ∼2.56 drum revolutions, which is consistent with experimental observations. An initial attempt has also been made to simulate the axial particle segregation. Although the initial results are promising, more work is clearly needed to establish a better picture of axial segregation.