Positron emission particle tracking (PEPT) with positron annihilation spectroscopy was possible to visualize the high speed behavior of particulates within a fluid bed in a mixer, which is an important basic operation in materials processing. This study provides new findings on a number of different regions with particle flow as well as on the performance resulting from different impeller blade geometries within a high shear mixer. There are marked differences in the flow pattern between the two blade designs. PEPT also revealed different characteristic impact velocities in each region (depending on the location within the granulator) as well as significant differences in powder flow when using flat or beveled impeller blades. These new results should prove useful for the design as well as for the operation and scale-up of high shear mixers.