Glass particles used in this study were characterized using QICPIC (manufactured by Sympatec GmBH). Distribution density of particle diameter is shown in Figure . These particles have a sauter mean diameter of 332 µm and are classified under Group B 24 characterized by good mixing behavior and vigorous bubbling 2 . Figure shows the cumulative distribution of sphericity and aspect ratio, having a median value of 0.93 and 0.97 respectively. In addition, Following particle characterization, tests were performed to estimate minimum fluidization velocity, U mf in all the columns. Further details regarding the procedure can be found in Vaidheeswaran at al. . Table summarizes values obtained in the 2.5-inch, 4-inch and 6-inch units which are consistent with previous findings of Cranfield and Geldart , Eisfeld and Schnitzlein 27 , Delbarre 28 , Di Felice and Gibilaro 29 and Rao et al. . Furthermore, Rao et al. suggest that the friction effects due to wall increases as the hydraulic diameter is reduced which leads to an increase in U mf for smaller geometries. Hence, a greater gas-phase inertia is required to support the weight of bed material and overcome resistance due to wall.