Spray models for discrete element simulations of particle coating processes

In the pharmaceutical industry, drum coating is routinely used for the production of film tablets. In order to produce a high-quality product, it is important to understand this seemingly simple process in great detail. In our study we present the implementation of three different methods to include spray coating in DEM simulations: (1) an enhanced “spray zone approach” working during run-time, (2) the “discrete drop method”, a novel approach for tablet coating also applied at run-time, and (3) the “ray-tracing method”, which is applied after the DEM simulation using the saved data. Each method is described in detail. For evaluation purposes, the different models were applied to simulate the same coating process, and the comparability, advantages and limitations are discussed. In general, all three methods can give comparable results. However, the spray zone approach depended heavily on its model parameters; the discrete drop method was more reliable and versatile. While the time resolution is higher for the first two methods listed above, the third is faster and more flexible.