(237c) Estimating Aggregation Efficiency from Observation of Flow Behaviour in a High Shear Mixer

High speed images of the bulk motion in a high shear granulator have been analysed using particle image velocimetry (PIV) to obtain surface velocity fields. The surface velocity field is found to contain a systematic component and an apparently random component induced by particle-particle collisions. This random component is found to exhibit a Gaussian distribution, allowing the kinetic theory of granular flow to be used to extract the granular temperature from the velocity field. The granular temperature is then used to estimate the collision frequency of granules within the bulk flow. Aggregation rates were determined experimentally for the system calcium carbonate ? polyethylene glycol from temporally resolve granulate size distributions measured offline. A binary aggregation population balance equation was fitted to the temporal granule size distributions using a discretised population balance model. For corresponding time points high speed images were recorded of the granular bed and collision frequencies estimated. Using the collision frequencies and the fitted aggregation rates, aggregation efficiency was estimated for the duration of the granulation experiment. Aggregation efficiency was found to decrease with granulation time and to be of the order of 2e-8.