Visualization of the effect of a shroud on entrainment of fluidized solids into a gas jet

Submerged gas jets issuing into fluidized beds are used in many different industries and it is important to have a fundamental understanding of how the gas and surrounding medium interact - to understand the flow patterns and how the solids behave in the vicinity of the nozzle jet. Following the discussions of Bohnet and Teifke (1985) and Idelchek (1994) it was decided to qualitatively investigate the effects of altering the region surrounding the contact between the jet and the fluidized bed. Alteration of the flow pattern was accomplished using a semi-cylindrical shroud (0.035 m i.d. and 0.043 m long) that formed a physical barrier around the nozzle tip. The nozzle inner diameter was 0.0016 m i.d. and the motive gas flow rate was supersonic. Videos were recorded of the solids and gas flow patterns via a special transparent plate on the wall of the fluidized bed for a half-jet with and without a shroud at a superficial fluidization gas velocity of 0.11 m/s. Presented below are the original videos and observations derived from the two simple experiments in a fluidized bed with a rectangular cross-section (0.10 by 1.20 m and 2.0 m high). There was a significant difference in the flow patterns of the solids in the vicinity of the nozzle tip when the shroud was present. Furthermore, the jet expansion angle and penetration were observed to decrease by approximately 50% and 43%, respectively.