Acoustic fluidized bed hydrodynamics characterization using X-ray computed tomography

Abstract

Acoustic vibration in a fluidized bed can be used to enhance the fluidization quality of particulate matter; this particular noninvasive method provides no internal changes to the bed material structure. However, due to the complexity of this multiphase flow system, characterizing the hydrodynamics of a fluidized bed has become critical in understanding this system behavior. The local void fraction behavior in a cold flow 3D fluidized bed with and without acoustic intervention is investigated in this research. Several noninvasive techniques like gamma-ray computed tomography (GRT), X-ray computed tomography (XCT), or electrical capacitance tomography (ECT), can be used to study the void fraction distribution in multiphase flow systems. In this study, XCT imaging is used to determine the time-average local void fraction or gas holdup. Experiments are implemented in a 10.2cm ID fluidized bed filled with glass beads or ground walnut shell, having a material density of 2500kg/m3 and 1440kg/m3, respectively, and particle size ranges between 212 and 600μm. In this study, three different bed height-to-diameter ratios are examined: H/D=0.5, 1 and 1.5. The loudspeaker’s frequency, used as the acoustic source, is fixed at 150Hz with a sound pressure level of 120dB for glass beads, and 200Hz and 110dB for ground walnut shell. Local time-average gas holdup results show that the fluidized bed under the presence of an acoustic field provides a more uniform fluidization, the bed exhibits less channeling, and the jetting phenomena produced by the distributor plate is less prominent when compared to no acoustic field. Thus, acoustic intervention affects the local hydrodynamic behavior of the fluidized bed.