Blade–granule bed stress in a cylindrical high shear granulator: I—Online measurement and characterisation

Abstract For high shear granulators, the rotating impeller blades exert forces on the granules, which are subsequently transmitted throughout the granule bed through inter-granule collisions. The effect of these collisional stresses on the granule growth behaviour is varied; as the granules could deform, consolidate and/or break under stress. This paper focuses on the normal stress between the blade and the granule bed in a cylindrical high shear granulator, which was directly measured using a custom-built telemetric impeller pressure sensor system. The stresses, evaluated at different operating conditions (impeller speed) and granule bed attributes (bed load, granule size and granule/particle type) were also fitted to a stress model derived based on the inertial force transferred from the blade to a continuous, cohesionless granule bed block. For the granule bed velocity and height parameters required in the model, the surface velocity of the bed at the sensor region and the bed height near at the wall, measured by high speed imaging, were used. A surface velocity corrected blade–granule bed stress model to account for the use of surface velocity and the effect of different flow regimes enabled much improved prediction of the stress for all types of dry granule beds used in this study. The effects of some individual granule/particle properties such as size, shape and strength on the stress were also negligible provided that the bulk flow behaviour is similar.