Executive Summary : | Powdered materials, characterised by their frictional, collisional and at times cohesive interactions, pose several problems in their flowability. The frictional and cohesive interactions can cause flow clogging and sticking of particles to the shearing boundaries as well as between themselves thereby hindering smooth operation. Such occurrences are encountered frequently in pharmaceutical industries handling powdered material in various operations and at differing lengthscales which eventually leads to inferior product quality. A solution, used frequently in these industries, is to add another fine, cohesive powder in small concentrations which acts as a lubricant between larger particles, thereby improving their flow properties. While the type of lubricant materials are standardised and their effect on final product quality is known very well, the underlying mechanism of the lubrication process is understood quite poorly. The lack of this knowledge precludes the availability of
predictive tools for lubrication, thereby posing difficulties while dealing with different powders encountering newer problems.
The primary objective of this work is carry out a fundamental study of the shear flow of granular material in the presence of lubricant particles. The work will be carried out for a range of particles, including typical pharmaceutical powders, in presence standard lubricants. Two different shear geometries, widely used for model studies, will be considered, viz., chute flow and Couette geometry, to study the effect of nature and extent of the imparted shear on the lubrication behavior. The experimental part of the work will involve high speed camera imaging and visualisation, image analysis and torque/stress measurements. This will be complemented by discrete element method (DEM) simulations for model spherical particles using open source softwares and for highly aspherical, plate-like powders and lubricants using proprietary software. The simulation parameters
will be tuned using experimental measurements. The flow profiles, concentration distributions, stress variations obtained from both studies will provide wealth of information to understand the primary lubrication mechanism.
The proposed work also opens up a newer fundamental research area within the significantly studied domain of granular systems, lying at the interface of dry granular flows, cohesive granular material and de-mixing of bi-disperse particle systems. The outcome will provide impetus towards newer theoretical models and pave the way for further innovative and significant research work. More importantly, it will provide a sound fundamental base to improve and optimise various industrial processed handling powdered materials, thereby enhancing the final product quality. |