An Experimental Investigation of Throughflow Velocities in Two-Dimensional Fluidized Bed Bubbles: Laser Doppler Anemometer Measurements

Abstract

Detailed nonintrusive measurements have been made to determine the throughflow velocity in isolated fluidized bed bubbles. In air-fluidized beds, the throughflow component has been rather neglected and measurements of the visible bubble flow alone have, therefore, failed to clarify the overall distribution of gas flow between the phases. A single component fiber optic laser Doppler anemometer was used to map the fluid flow through a bubble rising in a two-dimensional bed. The bed was fluidized at a superficial velocity slightly higher than incipient. The conditioned sampling technique developed to characterize the periodic nature of the bubble phase flow revealed that the throughflow velocity in two-dimensional beds increases linearly with increasing distance from the distributor, thereby enhancing the convective component in the interphase mass transfer process. Bubble growth was accounted for and the end-effects were minimized. Dependence of the bubble throughflow on the elongation of the bubble was observed thus confirming the theoretical analysis of some previous investigators. However, experimental evidence presented in this paper showed that the existing models fail to accurately predict the convective component in the bubble phase of two-dimensional fluidized beds.