(425a) Numerical Modeling Of Particle Agglomeration By Dynamic Liquid Bridge

In fluidized bed granulation, a binder solution is sprayed to fluidized particles and the particles are agglomerated by liquid bridge of the sprayed binder, resulting in particle size enlargement by the agglomeration. This liquid bridge formed between particles is not static and can be easily compressed, deformed, and ruptured, because the particles inside the granulators are always moving. Therefore, particle agglomeration by such a “dynamic” liquid bridge should be modeled to understand micro scale particle agglomeration mechanism inside the granulators. In this study, modeling of the dynamic liquid bridge between two particles was performed by a numerical approach.

Numerical modeling of the dynamic liquid bridge between two particles was conducted using a coupling simulation of a discrete element method (DEM) with a computational fluid dynamics (CFD). In this simulation method, a particle motion was solved by the DEM, and a liquid–gas two-phase fluid flow consisting of a liquid bridge was simulated by the CFD. To solve governing equation of the liquid–gas two-phase fluid flow, the constrained interpolation profile (CIP) method was used. A surface force acting at an interface between liquid-gas-solid phases, i.e., contact line, was calculated by a continuous surface force (CSF) model so that a wetting behavior of a droplet on a particle was simulated. A capillary force acting on the particles was calculated by integrating the surface forces of the contact line. A viscous force acting on the particles was simulated using a immersed boundary (IB) method.

A wetting behavior of a droplet on flat and curved surfaces with different contact angles (different hydrophilicity/hydrophobicity) was initially simulated. Repealing and spreading of the droplet was well simulated. A break up behavior of a liquid bridge between two spheres was then simulated, and the simulation result showed good agreement with an experimental result. Finally, particle coalescence and rebound mediated by the dynamic liquid bridge were simulated at various conditions, and key parameters determining the particle agglomeration were investigated. Consequently, numerical modeling of the dynamic liquid bridge between particles was successfully performed. This numerical approach can provide significant insights into a micro scale mechanism of particle agglomeration in fluidized bed granulation as well as the other wet granulation processes.