Coalescence of deformable granules in wet granulation processes

In this work, the coalescence of deformable granules in wet granulation processes is modelled. The model accounts for both the mechanical properties of the granules and the effect of the liquid layer at the granule surface. It is an extension to the model of Ennis et al. (1991) to include the possibility of granule plastic deformation during collisions. The model is written in dimensionless groups such as viscous and deformation Stokes numbers and the ratio of granule dynamic yield strength to granule Young's modulus (Yd/E*). These variables are bulk parameters of the powder‐binder mixture and also functions of the process intensity. The model gives the conditions for two types of coalescence–type I and type II. Type I coalescence occurs when granules coalesce by viscous dissipation in the surface liquid layer before their surfaces touch. Type II coalescence occurs when granules are slowed to a halt during rebound, after their surfaces have made contact. The model explains some of the trends observed in the literature, are preliminary validation of the coalescence criterion with drum granulation data is encouraging. An extension is also made to the case of surface dry granules, where liquid is squeezed to the surface during granule deformation.