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Liquid-grains interactions - Pascal Raux

Surface du Verre et Interfaces, Saint-Gobain Recherche, Aubervilliers

In this seminar, I will illustrate the diversity of liquid-grains interactions through various examples inspired from the industry :
- Adding liquid increase the cohesion of a granular material. Most studies focus on the limit with little liquid, where only independent capillary bridges are present. We discuss here the cohesion of unsaturated granular media with a larger liquid content. From a paste obtained by mixing glass beads to the liquid, we cast a compact beam and study its rupture under its own weight. For high liquid contents, the cohesive strength increases with the amount of liquid. This behavior diverges from what is expected from individual capillary bridges, suggesting a role of the liquid repartition in the granular medium.
- The cohesion induced by the liquid allows the formation of aggregates. We propose a model experiment for the granulation process : a bead-liquid paste is vibrated at large amplitude. We study the size of the agglomerates formed, and compare our results with available data from industrial high-shear granulation processes.
- I will finish by some results on suspensions, i.e. when the proportion of grains and liquid are reversed. For dilute suspensions, it is well known that the particles increase the effective viscosity. However, this only holds in the continuum approximation, and should fail in a confined situation such as a liquid sheet. I will present results on the dynamics of a thin film of suspension formed upon the impact of a suspension drop. We show that the atomization process varies when the thickness of the liquid film is smaller than the particle’ size, leading to a loss of stability of the sheet. Our results highlight the influence of capillary effects in this confined flow.


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