Modelling of droplet absorption and evaporation during pharmaceutical tablet coating

The shelf life of a pharmaceutical tablet is affected by the amount of water that interacts with it during the aqueous film coating process. The purpose of this work is to simulate the spreading, absorption and evaporation of water droplets after impact on a porous tablet core. We divided the spreading, absorption and evaporation phenomena into three separate phases: the kinematic, the capillary and the evaporation phases. For the kinematic phase, we modified 1-D spreading models found in the literature which solve the kinetic energy balance equation. Subsequently, for the capillary phase we solved the Navier-Stokes equation using the lubrication approximation theory. For the evaporation phase, we developed a novel model that treats the tablet as a particle with a wet core surrounded by a dry crust. Our numerical results were in good agreement with recent experimental data found in the literature