Dynamics of particle wetting in wet granulation: Micro-scale analysis

Abstract

Particle wetted surface area affects the probability of particles aggregation in the fluidized bed wet granulation process. Modeling the dynamics of binder spreading over particles and binder evaporation can help to determine the wetted area in time. To this end, a possible chain of events in the particle/droplet level has been proposed to reveal the effect of binder spreading and evaporation on granulation. Then, a second-order model has been introduced based on the key points of spreading, including the initial spreading radius, d∗, and the equilibrium radius. The model is compatible with conventional laws that R(t)∝t0.5 in the inertia-dominant regime and R(t)∝t0.1 in the viscous dominant regime. The binder evaporation has been considered in two situations including the simultaneous evaporation with spreading and evaporation after spreading. In the latter situation, the evaporation model of a sessile droplet on a substrate was employed while in the former situation the evaporation model has been merged with the proposed spreading model. This model has been validated by experimental data and two available theoretical models of spreading. In addition to simplicity and no need for tuning parameter, the present model shows the acceptable accuracy in comparison with the other models. Finally, the effects of impact velocity, equilibrium contact angle, droplet diameter, and temperature on the dynamics of spreading diameter have been investigated using the present model.