Characterization of de-fluidized regions in the wake of submerged objects in a small particle fluidized bed

• The de-fluidized wake region behind submerged objects in a fluidized bed is studied.
• The de-fluidized region consists of a dead region in the near wake.
• The dead region is followed by a cylindrical percolating region.
• Voids induced by the submerged object cause gas separation from the submerged body.
• The de-fluidized region significantly impacts object buoyancy.

The structure of the de-fluidized hood, an area of un-fluidized material found in the wake of submerged objects, is studied with special interest on the internal de-fluidization levels and shape of the hood. Previously, the structure of the region was determined based on indirect photographic evidence. The findings on the structure of the de-fluidized region allow for better prediction of the buoyancy on submerged objects within a fluidized bed.In the present study the force imparted by the wake region at various depths on a submerged object within a fluidized bed of “Geldart A” particles was measured providing insight into the size of the region, as well as levels of the fluidization within the wake. Additionally, bed collapse with an object near the surface and the ability of that free surface to support weight were measured. The results show the region to have multiple regions: a stagnant dead layer directly above the object, topped by a larger percolating region with particle circulation and an expanding region. The overall shape is found to resemble a cylinder with a rounded top. The roles played by voids generated by the submerged object, angles of repose and secondary circulation are discussed.

The de-fluidized hood in the wake behind a sphere in a fluidized bed of Geldart A particles operating at minimum fluidization velocity is shown. Arrows show the pattern of gas re-entry into the wake and ellipses represent voids. The hood consists of a dead region followed by a percolating region.Figure optionsDownload as PowerPoint slide