Flow dynamics and segregation of dry granular materials and slurries

Granular flows and segregation are important in a wide range of industrial and geological situations varying from mixing powders and formulation for pharmaceutical industries to landslides. The goal of this work is to better understand both the flow dynamics and the segregation in granular materials using a prototypical system---a quasi-2D rotating tumbler. Both dry granular matter and wet granular matter (slurries) are considered. Particle Image Velocimetry (PIV) coupled with Particle Tracking Velocimetry (PTV) is used to measure the dynamics in the flowing layer to investigate the effect of the interstitial fluid. Under slurry conditions the flowing layer thickness and the angle of repose are higher than the dry counterpart for the same sized beads tumbled at the same angular velocity. However, the surface velocity and shear rate are smaller when the interstitial fluid is a liquid rather than air. The velocity profile is nearly linear throughout the layer except for a region near the fixed bed where the velocity profile is logarithmic. Experiments on granular segregation in a circular tumbler reveal that for particle size and density combinations where percolation and buoyancy both contribute to segregation, either radial streaks or a "classical" core can occur, depending on the particle size ratio. Mixing is observed instead of segregation when the denser beads are larger than the lighter beads so that the ratio of particle sizes is greater than the ratio of particle densities. Changes in the tumbler shape introduce chaos in the system and causes segregation patterns to differ significantly in shape. Regardless of the differences in the shape of segregation pattern for these tumblers, the final mixing efficiency predominantly depends on the particle parameters.