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Jetting Observations In a Cold-Flow Fluidized Bed

Nathan P. Franka, Iowa State University, 2025 Black Engineering Building, Ames, IA 50011 and Theodore J. Heindel, Department of Mechanical Engineering, Iowa State University, 2025 Black Engineering Building, Ames, IA 50011.

Jetting in a 10.2 cm diameter cold-flow fluidized bed with a perforated plate gas distributor is observed using X-ray computed tomography (CT). The bed is filled with one of three 500-600 micron materials (glass beads, ground walnut shell, or ground corncob), and operated over a range of superficial gas velocities (1.25Umf 3Umf, where Umf is the minimum fluidization velocity). Local time-averaged gas holdup is determined in the entire bed from the CT data. Regions of high time-averaged gas holdup are observed directly above the perforated plate showing jet penetration into the fluidized bed.

The perforated plate is composed of 62 1-mm diameter holes arranged in a circular pattern. The CT images clearly show that not all aeration holes are active at low superficial gas velocities and the number of active aeration holes increases with increasing Ug. The more dense glass bead bed has less active holes at the same Ug when compared to the less dense beds of ground walnut shell or ground corncob. However, all aeration holes are active, for all bed materials, at the highest superficial gas velocities of this study. The CT images also show that the jets in the center of the bed dissipate before those near the bed walls. Eventually, all jets lose their identify.