Solids motion caused by a bubble in a fluidized bed

Abstract

Theoretical analyses of the motion of a sphere or a cylinder through an inviscid fluid have been applied by previous authors to consideration of particle motion caused by a single bubble in a fluidized bed. The theories, however, take no account of the wake attached to a bubble; examination of the effect of the wake on the interpretation of displacement profiles has shown that the wake size can readily be calculated from experimental profiles using a thin layer of tracer particles. Profiles obtained in a two-dimensional bed of glass ballotini indicate that the wake area is 13–28% of the bubble area. The passage of a bubble across any horizontal plane causes a downward displacement of the dense phase to replace the wake material. Superimposed on this net downward displacement is a drift movement, similar to that of the inviscid fluid theories. Only a small area at the top of the peak of the drift profile crosses the horizontal level under consideration; this constitutes an additional quantity of material displaced upwards by the bubble with area about 5% of the bubble area. Consideration in the same terms of the results of other authors indicates that these conclusions are roughly applicable also to three-dimensional beds.