An Experimental Study of Bubble Size Distribution in a Two-Dimensional Gas-Solid Tapered Fluidized Bed

Bubbles are very common in gas-solid fluidized bed reactors. They form the core of fluidized bed hydrodynamics, which affects the heat transfer, mass transfer and reaction kinetics as well as mixing and segregation behaviour of fluidized beds. The bubble behaviour of columnar fluidized beds is well studied and reported in the literature. However, there is a lack of study of bubble behaviour in tapered/conical fluidized beds, which is significantly different from the columnar fluidized beds. To study bubble behaviour, experiments were carried out using Geldart group B glass beads in a laboratory-scale pseudo-two-dimensional tapered fluidized bed with air as the fluidizing medium using high speed imaging technique. The images that were captured using high speed camera, were further processed using digital image analysis technique to quantify the bubble phase from the emulsion phase. The bubbles were classified into three groups: small (0-3 cm), medium (3-6 cm) and large (>6 cm), based on their diameters. The effects of tapered angle and superficial air velocity on the bubble size and its’ distribution were studied along the vertical and lateral directions. It is found to be affected by these parameters significantly. Further, coalescence and break-up of bubbles that were observed in the bed is also found to affect the bubble size and its’ distribution.