Bed height and material density effects on fluidized bed hydrodynamics

Characterizing the hydrodynamics of a fluidized bed is of vital importance to understanding the behavior of this multiphase flow system. Minimum fluidization velocity and gas holdup are two of these key characteristics. Experimental studies addressing the effects of bed height and material density on the minimum fluidization velocity and gas holdup were carried out in this study using a 10.2 cm diameter cylindrical fluidized bed. Three different Geldart type-B particles were tested: glass beads, ground walnut shell, and ground corncob, with material densities of 2600, 1300, and 1000 kg/m3, respectively. The particle size range was selected to be the same for all three materials and corresponded to 500–600 μm. In this study, five different bed height-to-diameter ratios were investigated: H/D=0.5, 1, 1.5, 2, and 3. Minimum fluidization velocity was determined for each H/D ratio using pressure drop measurements. Local time-average gas holdup was determined using non-invasive X-ray computed tomography imaging. Results show that minimum fluidization velocity is not affected by the change in bed height. However, as the material density increased, the minimum fluidization velocity increased. Finally, local time-average gas holdup values revealed that bed hydrodynamics were similar for all bed heights, but differed when the material density was changed.