A DEM study of the mixing of particles induced by a flat blade

Powder mixers often deploy blades of various kinds to impart convective motion to particles. Here, a single blade is followed through a bed, an arrangement that has previously been effective for understanding mixing, to investigate the effects of blade rake angle and blade speed on the blade-induced mixing behaviour of particles by means of the Discrete Element Method. When the blade rake angle phi is varied from 45 degrees to 90 degrees and then to 135 degrees at a fixed blade speed of 0.2 m/s, Froude (Fr) number varies from 0.144 to 0.10 and then back to 0.144, respectively and the horizontal force on the blade is found to decrease monotonically with increasing phi if the blade immersion depth is held constant. This force is not affected by the blade speed in the range of 0.2-0.6 m/s (or in the Fr number range of 0.14-1.3) at phi=135 degrees. For phi=135 degrees, particle dispersion is found to be the largest at the top and bottom of the bed. Convective mixing behaviour of particles is shown to be predictable by velocity-field based particle-motion simulations. Dynamic similarity is confirmed to occur in geometrically similar systems in the macroscopic quantities such as the non-dimensional horizontal force on the blade and scaled average horizontal particle velocity. Further, the single-blade model can be used to understand mixing in a vertically shafted two-bladed cylindrical mixer. The results demonstrate the potential for utilising the results developed for the single-blade model in much complex industrial systems. (C) 2012 Elsevier Ltd. All rights reserved.