Granular flow in a planetary mixer

Wet massing granulation is widely used within the particle-forming industries. However, the process is difficult to monitor and control and the structure of the granular flow is poorly understood. Positron emission particle tracking was used to study powder flow patterns in a planetary mixer. Prior to studying granulating systems, a dry system of a model pharmaceutical formulation was studied to develop understanding of the interaction between mixer parameters such as the speed, level of fill, and the structure of the flow. Two quite different regimes of tracer motion exist. Within the central core of the vessel the powder behaviour was determined by the rapid movement of the agitator. In contrast, in the regions close to the wall, the material was found to exhibit ascending steps dictated by the planetary rotation. These two forms of behaviour were observed at all levels of fill and agitator speeds. The angular velocity and total speed scaled with the agitator speed. Further analysis showed that the radial and axial velocities of the tracer were up to an order of magnitude lower than the tangential component.