(21e) Flow Structure Study on Expanded Bed in Gas Fluidization of Fine Ellipsoids
Combined approach of computational fluid dynamics for gas phase and discrete element method for particles (CFD-DEM) is used to draw a picture of the typical three stages in expanded beds in gas fluidisation of fine ellipsoids. The results illustrate that in the start-up stage, the bulk disconnects into two major bulks with a lowest contact force on the axial direction, especially for flat and elongated particles. The positions of the lowest point of contact force only slightly change with time for oblate and prolate particles, but it moves from bottom to top for spheres. A slower gas introduction process has a mildest change in bed height (porosity). The fractures gradually disappear when the cohesive forces become smaller. In the transition stage, when aspect ratio deviates from 1.0, the pressure drop fluctuation significantly increases. In the stable stage, when the aspect ratio decreases or increases from 1.0, the contact forces and van der Waals forces increases, and the particle-fluid forces become less uniformly distribution in the beds. Spherical particles have the lowest porosity increment in the expansion process. Ellipsoidal particles undergo an orientation rearrangement during the expansion process.
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