Effect of humidity on the static angle in granular systems

Abstract

The purpose of the present work is to study the influence of humidity effect on the static angle for single particles with diverse sizes on surfaces with differing roughness. The aim is to provide information about the characteristics of cohesive forces between grains and rough surfaces with different grain geometries. The study has an experimental part and it is complemented by Monte Carlo simulations (MCS) and an empirical formulation of the dependence of the critical angle on two important parameters of the problem. The experimental device consists of an inclined surface that allows studying the evolution of the static angle (Ɵs), that is, the angle at which a 50% percent of spheres are put in motion. Relative Humidity (RH) is controlled through hygroscopic salts saturated solutions. Values ​​obtained at different humidity rates are compared. For the MCS, the balance of the moments applied to the particle and necessary for its destabilization are taken into account as a basis for calculating the probabilities for movement. Simulations help to establish a fitting curve that is able to describe the complete set of results by correlating the fitting parameters with the surface roughness and the Bond number for the particles. We determine that for systems with high humidity, the formation of liquid bridges between particles affects the static angle for the onset of movement and this angle decrease as the diameter of the spheres increases. The type of surface has an important role on the static angle values.