Flow Patterns in Particle Beds

Abstract

THE technique of observing gas-flow patterns in fluidized beds described in a recent communication¹ is a useful contribution to the methods available for investigating fluidization behaviour. A comparable technique has been developed here using dye injection for tracing the flow pattern of water passing through particle beds. Though this technique was found useful in the pre-expansion stage, it was the reverse during bed expansion when it actually tended to mask the interesting phenomena shown in Fig. 1. These photographs were taken by transmitted light without the use of dyes, and show the activation of a bed of 100µ glass spheres by water. Local bed expansion or increased voidage is indicated by increase in transmitted light. Photograph C13 shows the approximate steady-state conditions in a bed which, viewed superficially, has all the appearance of uniform and smooth participate fluidization. The series A1–A12 (of which A1, 3, 6 and 12 are reproduced) shows the development of a flow pattern in the same bed at a much lower superficial water velocity. The last of that series again approximates to steady-state conditions, the only changes thereafter being a slow meandering of the flow channels. Not seen in the photographs but observed visually are occasional series of mushroom-shaped low-density discontinuities rising in one or more of the channels.