Break-up of cylindrical clusters of solid particles under gravity flow in a 2-dimensional column

A 0.012 m x 0.12 m two-dimensional column has been used to study gravitational motion and break-up of 0.032 m diameter cylindrical clusters of solid particles. Clusters were analysed by means of a KODAK SPIN PHYSICS SP2000 Motion Analysis System. Shape deformations, volume expansions and surface perturbations have been estimated for clusters of various solids at different distances from the point of release. Aspect and expansion ratios, times for onset of surface perturbations, and also cluster fall-velocities have been measured. Depending on the nature of the solids, three types of cluster have been considered: undeformable clusters, gas-impermeable clusters and gas-permeable clusters. Particle-to-particle forces are considered responsible for compacting solids of undeformable clusters. Two dimensionless numbers have been developed for the case of gas-impermeable clusters: the first is related to the aspect ratios of the cluster, whereas the second is related to the time needed for the appearance of surface perturbations on the cluster front. It has been suggested that the ratio of particle to cluster size controls expansion and break-up of gas-permeable clusters.