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 ø is varied from 45° to 90° and then to 135° 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 ø 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 ø=135° For ø=135°, 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.