Evaluation of Coating Variability in a Wurster Coater via Ray Tracing and Spray Zone Methods

Abstract

This study investigated systematically the coating processes of ellipsoidal tablets in a Wurster coater by coupling CFD-DEM simulations and postprocesses. The tablets were represented by superquadrics in the CFD-DEM simulations. Two postprocessing methods (i.e., the ray tracing method (RTM) and the spray zone method (SZM)) were established and compared. Their algorithms were introduced in detail, and the effects of important model and operation parameters were analyzed, including the number of rays, the number of facets per tablet, the time step of the postprocesses, the fluidizing gas velocity, and the spray angle. Implemented in a postprocessing mode, the two methods provided a flexibility to simulate different spray settings with only one round of DEM runs. The RTM is able to provide multiple pieces of information relating to the coating processes but with a relatively high computation cost. By contrast, the SZM is simpler and faster but cannot estimate the intratablet coating variability and the coating efficiency. Besides, it is generally difficult to define a spray zone accurately under various conditions for this method. There is no obviously better choice at this stage, and more comparisons with experiments should be implemented in the future.