Humidity-Induced Cohesion Effects in Granular Media
- PDF / 133,005 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 325 Views
Humidity-Induced Cohesion Effects in Granular Media Nathalie Fraysse1, Luc Petit Laboratoire de Physique de la Matière Condensée, UMR 6622 CNRS - Université de Nice, Parc Valrose, 06 108 Nice cedex 2, France. 1 [email protected] ABSTRACT Experiments were performed under accurately-controlled humidity conditions in order to quantify effects induced by humidity on granular materials. Measurements of the maximal stability angle of a pile made of small glass beads are reported as a function of the relative vapor pressure in the cell, up to close to saturation. The comparison of the results obtained with fluids differing in their molecular interactions with glass, namely water and heptane, shows that the wetting properties of the interstitial liquid on the grains have a strong influence on the cohesion of the nonsaturated granular medium. This suggests that gravimetric experiments which could indirectly give information on the size of the capillary bridges that form between grains should be useful to understand the close connection that exists, through interparticle forces, between microscopic properties such as wetting properties and surface roughness of the grains, and global-scale properties of the pile, as its stability and flowability. INTRODUCTION The wide variety of behaviors observed for dry granular media according to various external constraints originates from two main interparticle forces that are the solid friction and an elastic repulsion. If now considering wet granular media, capillary forces and possibly viscous forces have also to be taken into account; at the global scale, cohesion and lubrication effects, which are totally absent in dry sand, may appear as the result of these additional local interactions between grains. Such humidity-induced effects come into play in many applications that involve granular materials. The presence of an interstitial liquid can have various causes; the atmospheric humidity is the most obvious and maybe the most common one as, in usual practice, grains are most of the time stored and handled in the open air. Note that the consequences of humidity effects are negative in most of industrial processes (e.g. blocked flows from hoppers or silos) but they might be positive: For instance it is conceivable that humidity effects oppose the annoying segregation phenomenon. Therefore it is of great importance to precisely know and to fully understand humidity effects on granular media, from a practical point of view as well as from a fundamental one. In this paper we present experiments that we have performed under accurately-controlled humidity conditions in order to quantify such moisture-induced effects. We report the quantitative measurements of the maximum angle of stability of a pile, as a function of the relative vapor pressure, up to close to saturation. We also investigate the influence of the wetting properties of the interstitial liquid on the grains on the stability of the pile.
EXPERIMENT BB7.1.1 Downloaded from https://www.cambridge.org/core. Macquarie University, on
Data Loading...
