Mechanical Strength of Humidified Glass Beads

Abstract

In this work we measure the mechanical strength of a bed of glass beads that has been previously subjected to a controlled flow of humid air by using a fluidized bed setup. The material is first initialized in a reproducible state by subjecting it to a high flow of dry air that drives the bed to bubbling. Then the gas flow is abruptly turned off and, once the bed is settled, it is subjected to a small flow of humid air during a certain period of time. Water moisture is added to the fluidizing air by bubbling it through water. The relative humidity and dew point of the air are monitored on-line by using humidity sensors upstream and downstream of the bed. After the stationary condition is reached, the bed is slowly tilted and the avalanche angle and depth are measured. From Coulomb’s wedge model and Rumpf’s equation using the attractive capillary force, the predicted angle of avalanche of the humidified samples is shown to be close to the experimental value.