Rheological modeling of particle flows in high shear granulation

Licentiatavhandling, 2014

High shear granulation is an important process in a wide variety of applications, more specifically in pharmaceutical industries as a basic step in the tableting process. The process includes two major steps: dry high shear granulation and wet high shear granulation. It aims at producing granules with a specific size and material composition. The quality of the process is determined by the flow regime. Therefore, a better understanding of the flow regime is required. Computational simulation of such systems is traditionally performed by tracking each particle and resolving its binary collision and interaction with other particles. This approach is not feasible for industrial granulators with billions of particles. The aim of this study is to evaluate the possibility of applying various continuum modeling options in studying dense or multi-regime granular flows. Kinetic Theory of Granular Flow formulates the dilute parts of the system, whereas there is no strong agreement on any approach to modeling dense granular flows. In this study, a recent model proposed by Jop et al. is applied as an alternative to the model by Schaeffer, traditionally used for such flow regimes. The results show that the present model is not only simple, but also clearly predictive. Besides, considering the simplicity of the model compared to its alternatives (KTGF or DEM), adding more details to develop the model can be performed with fewer obstacles. In order to validate the model proposed in this study, model results are compared with experiments performed in a disc impeller granulator. The experimental results were analyzed using advanced techniques including a high speed camera and Particle Image Velocimetry (PIV). Keywords: high shear granulation, continuum modeling, rheology, disc impeller