The presence of moisture in powders and grains drastically changes the mechanical properties of the materials. Inter-particle cohesion due to capillary bridges, causes grains to agglomerate into clumps of sizes much larger than the size of the constituent particles. Besides lacking a complete understanding of the effects of inter-particle cohesion on granular mechanics, the agglomeration of granules makes the processing of such materials challenging, in particular during drying under agitation processes. The methods of drying a mixture of particles and liquid affect the state of agglomeration of the final dried product, particularly through the influence of impacts and shear forces on the agglomerates.
The project is based on the development of model experiments to understand and model the mechanics, size distribution, and time evolution of particle agglomerates. By controlling cohesion and grain properties, we hope to shed some light on the mechanical behavior of agglomerates to develop models at agglomerate scales. In particular, we consider the breakup of model agglomerates, with an application to more efficient drying of powders. Besides causing trouble in the processing of such materials, agglomerates can also sustain humidity within them, reducing the overall ability to dry such bulk materials.
During the first year of the project, different experimental tools were developed and tested with model particles - spherical glass beads - and without considering heat exchange and drying. We developed an oscillating system consisting of a mechanical shaker and a quasi-2D transparent box allowing us to observe the agglomerates. Preliminary tests with model glass beads and water have been performed to probe the role of acceleration and amplitude of oscillation on the agglomerate sizes. A second system, relying on an agitation provided by a turbulent airflow has been designed and led to some first results. Finally, we initiated model experiments consisting of the impact of isolated agglomerates on a solid surface to probe their mechanical properties and fragmentation.