Chi-Hwang Tai

Effect of moisture content on the convection motion of powders in a vibrated bed

Abstract The cohesive forces between grains, such as capillary forces, van der Waals forces and electrostatic forces, play significant roles in the motion of particulate solids. This paper intends to investigate the influence of moisture content on the convection motion of wet granular materials in a vibrated bed. The rising velocity of a larger bead in the background of smaller beads in a vibrated bed was used to characterize the strength of the convection cells. It was found that the moisture content in the bed influenced the rising velocity of the larger bead. Under some specific vibration conditions, the rising velocity of the larger bead increased with the addition of a small amount of water. In these cases, the small amount of water produced a lubrication effect which resulted in the enhancement of the convection motion of the bed. With greater amount of water, the rising velocity of the larger bead decreased due to the viscous force and liquid bridge force between the water and beads.

The flow behavior of granular material due to horizontal shaking

This paper studied the convection phenomena that occurred in a granular bed under horizontal vibration. High-speed photography was employed to measure the movements of particles. The fields of the instantaneous velocities and the long-term velocities were plotted. Two symmetric convection rolls were observed. The granular temperature distributions were also measured and analyzed. The controlling parameters included the acceleration amplitude and the wall condition. The convection strength was found to increase linearly with the total granular temperature in the bed.