(221c) DEM Study of a Batch Blending Process

Mathematical models, like discrete element method (DEM), developed from micro-mechanics principles and calibrated with experimental data, provide process understanding and prove to be a resource- and time-saving alternative when compared to experimental methods for process design. These savings are noteworthy when the process is powder mixing, which is a crucial step that dictates blend uniformity ahead of any further processing and dose creation. DEM is often used to simulate material flow as it treats the particles as discrete entities. The success of DEM models significantly depends on thorough calibration, which in turn, relies on the quality of material properties testing. Determining accurate values for bulk density, cohesion, particle/wall friction and particle/particle friction, are consequential in ensuring the accuracy of the DEM model. This quality also includes the exactness of the material in the application that the DEM model is attempting to simulate. Often, materials that are deemed a close-enough match or surrogates of the actual material are utilized to obtain properties for DEM calibration. A material mismatch can reduce the representativeness of the simulation and therefore the usefulness of the model to the physical process it is aiming to mimic. In this study, the material testing was performed on the actual materials used in the blending operation to ensure that the measured properties represented the blending process.

The material testing was conducted on two materials - one cohesive and the other free-flowing - that were blended in a ribbon blending operation. This research aims to simulate the mixing dynamics of the overall cohesive blend within the batch ribbon blender using DEM to inform the development of strategies to promote homogeneous composition and minimize areas of segregation. The results from the simulation were validated against the experimental blending data. Parameters of interest that were explored include the relative standard deviation (RSD) and stagnant zones, which are critical quality attributes in powder mixing processes.