Scaling factors in granular flow—analysis of experimental and simulations results

The relationship between the design of powder mixers and their performance is of crucial importance for many industrial processes and yet is not well understood. Here the flow patterns generated by an agitator carrying a long flat blade were compared to those generated by a single ploughshare using positron emission particle tracking and DEM. The performances of these agitators were also assessed against those of multi-blade and multi-plough agitators. The powder flows created by the different designs had some qualitative similarities. Indeed, all the agitators were shown to generate a loop of circulation below the free surface of the bed. The radial support of each mixing element was also observed to act as a separatrix for the axial flow, leading to the formation of a loop of circulation on each side of the mixing elements, thus inhibiting axial convection of material. The single-blade agitators, be the flat blade or the plough, were found to induce a pulsing regime, this feature being also observe with the multi-blade agitators but with a lesser amplitude. For moderate agitator frequencies of rotation where inertial effects are negligible, fundamental characteristics of the flow patterns extracted from power spectra of axial displacements could be scaled with the number of blade passes.