Ray Casting DEM Simulation Data to Characterize the Spray Coating of Superquadric Particles

Abstract

Drum spray coating of tablets is a common unit operation in the pharmaceutical production process. Increasingly, the Discrete Element Method (DEM) is being used to study and optimize this process in order to improve the resulting tablet coating uniformity. Multi-spheres are a popular approach to shape approximation in DEM, but have been shown to be insufficient at modeling the bulk kinematics of certain tablet shapes. This work develops a method that enables the use of superquadrics in DEM to study inter- and intra-tablet coating variability. Specifically, a standalone C++ program is developed that models the spray by casting rays on data exported from DEM simulations. Acceleration techniques like spatial subdivision and bounding volumes are used to reduce the runtime, and an efficient intra-particle representation is developed and used to compute the intra-tablet coating variability. The final implementation is capable of processing a 180 second simulation containing 2 million tablets in just a few hours on a conventional desktop computer. Key parameters of the implementation are studied through benchmarks and suggestions of suitable values are made. The tool is finally used to show that the blockiness of the DEM shape representation has a significant impact on intra-tablet coating variability, but further studies are needed to better understand this effect.