UC San Diego

Suspensions or solutions of polymers are widely used in the pharmaceutical industry to coat tablets with different agents. These allow controlling the rate at which the drug is delivered, taste or appearance. The coating is performed by spraying and drying the tablets at moderate temperatures. The spreading of the coating on the pills surface depends on the droplet Webber and Reynolds numbers, angle of impact, but especially on the rheological properties of the drop. We present simplified models for the evaporation of suspension and solution droplets in a hot air environment with temperatures substantially lower than the boiling temperature of the carrier fluid. As the liquid vaporizes from the surface in the solution case, the solution becomes more concentrated, until reaching its saturation point. After saturation, precipitation occurs uniformly within the drop. As the surface regresses, a compacting front formed by the solid precipitate at its maximum packing density advances into the drop, while more solute continues