The rheology of dense granular flows in a disc impeller high shear granulator

• The aim is to improve the modeling of dense flow regions of High Shear Granulators
• The model developed in Jop et al. 2006 is evaluated in a disc impeller granulator
• The model describes the dense granular flow as a visco-plastic fluid
• The model predictions were validated against PIV and bed shape measurements
• The model was found to capture the general features of the flow

The aim of the present study is to evaluate the new approach to dense particulate systems proposed by Jop et al. [1], in the dense regions of a High Shear Granulator (HSG). Wet granulation in high shear mixers is a common process in pharmaceutical technologies and a good understanding of the local mixing and flow patterns is a pre-requisite for this step. In the aforementioned model a dense granular flow is characterized as a visco-plastic fluid. Therefore the local rheology of the system can be predicted assuming averaged and virtual properties and a constant solid volume fraction.A simple disc impeller granulator with glass spheres was chosen for this study. The dynamics of the system have been studied using several techniques including PIV analyses, CFD simulation and image processing. The flow behaviour has been characterized for various impeller speeds and particle loads. Several cases have been analyzed from different aspects both in experiments and through equivalent simulations to evaluate the validity of the model in these particular applications.Results look promising in spite of the simplicity of the model. The model was found to give a good general description of the flow field and bed shape. On the other hand the model is insufficient in some aspects; mostly related to the regions with low volume fraction. The next step would be to combine the model with conventional models on rapid granular flow such as Kinetic Theory of Granular Flows (KTGF).

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