Fracturing-induced fluidization of vibrated fine-powder column

Abstract

We experimentally investigate the effect of vertical vibrations on the brittle behavior of fine cohesive powders consisting of glass beads of 5 microns in diameter. This is an attempt to understand the sole role of vibrations in fluidizing Geldart's group C powders, which is known for posing difficulty while fluidization. We find that the cohesive powder column can be compacted, fractured, and effectively fluidized by increasing the strengths of external vibrations. This process of vibration-induced fracturing is summarized in a full experimental phase diagram showing four distinct phases of the vibrated powder column: consolidation (CS), static fracture (SF), dynamic fracture (DF), and convective fracture (CF). We find that the boundary separating the consolidated and fracture regimes depends on the dimensionless shaking strength, S. However, in the DF regime, the decompaction wave propagation speed normalized to gravitational speed is found to be independent of S. In order to reach our ultimate goal of effective fluidization of group C powders, we explore geometrical parameters like container shapes, sizes, and base conditions. We find that the circular cylinder with hemispherical base condition is the most effective container in order to achieve effective fluidization of group C powders when vibrated.