Effect of particle surface modification on the onset of spouting in a rectangular spouted bed

Experiments were conducted in a rectangular spouted bed to study the effect of surface modification of the particles on the gas-solid hydrodynamics. The surface was modified by doing coating the particles with acrylic paint. A completely different solid flow pattern was observed at the onset of spouting when coated particles were used. Instead of forming a cavity at the gas entry nozzle, particles from the top of the bed were fluidized at a particular gas flow rate, and a crack propagated downwards. After that, a big gas bubble formed at the bottom, which subsequently underwent bursting with the release of pressure. We report such hitherto unknown phenomena for a shallow granular bed for the first time. Instantaneous particle dynamics have been characterized using high-speed imaging. It is deduced that the cohesiveness of coated particles is the controlling parameter for this anomalous spouting behavior. Peak pressure drop and the corresponding superficial gas velocity for coated glass beads are more significant than uncoated particles for the same static bed height. A homogenous mixture of uncoated and coated glass beads exhibited bed characteristics as that of pure coated particles if the volume fraction of coated particles is greater than 20 %.