Detailed modeling and process design of an advanced continuous powder mixer.

A vertical in-line continuous powder mixing device (CMT - Continuous Mixing Technology) has been modelled with the discrete element method (DEM) utilizing a calibrated cohesive contact model. The vertical design of the mixing device allows independent control of mean residence time (MRT) and shear rate. The hold-up mass and outlet flow are controlled by an exit valve, located at the bottom of the in-line mixer. A virtual design of experiments (DoE) of DEM simulations has been performed and parameters such as particle velocities, powder bed shape, residence time distribution (RTD), travel distance, and mixing quality are evaluated for the complete operating space. The RTD of the DEM model has been validated with tracer experiments. The resulting RTD has been fitted with an analytical form (generalized cascade of n continuous stirred tank reactors) and utilized to study the downstream response of the continuous mixing device to upstream fluctuations in the inlet material stream. The results indicate a high mixing quality and good filtering properties across the operating space. However, the combination of low hold-up mass and high impeller speeds leads to a reduced filtering capability and wider exit valve openings, indicating a less desirable operating point.

Investigation of serrated roll surface differences on ribbon thickness during roller compaction.

Many parameters are considered when developing a roller compaction process. However, roll serration volume is generally not considered when using serrated rolls. It was hypothesized that serration volume of concavo-convex rolls can have a significant effect on ribbon thickness due to differences in nip angle. Experiments were conducted to investigate ribbon thickness using different roll sets having a range of serration volumes. Roll sets with approximately twice the serration volume produce ribbons 20-25% greater in thickness. These results correlated with physical measurements taken of the serrations from each set. Thus, differences in roll serration volume can significantly affect ribbon thickness.