Influence of air bubble size on float–sink of spheres in a gas–solid fluidized bed

The float–sink of density adjusted spheres of different diameter (10–40 mm) in a gas–solid fluidized bed was investigated at various bed heights (50–200 mm). The maximum density of floating spheres (ρfloat) and the minimum density of sinking spheres (ρsink) were determined by the float–sink experiments. The fluidized bed density (ρfb) was measured using the height and cross section of the fluidized bed and total weight of the fluidized media. The diameter of air bubbles at the bed surface was measured at each bed height, and was normalized by the sphere diameter. It was found that the value of ρfb–ρfloat approaches zero as the normalized bubble diameter decreases from 4 to 0.5 regardless of the sphere diameter. The value of ρsink–ρfb for sphere diameter = 10 mm approaches zero as the normalized bubble diameter decreases from 4 to 1.5, whereas the value for sphere diameter = 20–40 mm rises from zero as the normalized bubble diameter decreases from 1.5 to 0.5. The float and sink of spheres basically tend to follow the fluidized bed density with decreasing the normalized bubble diameter. However, relatively larger spheres do not sink based on the density difference as the normalized bubble diameter decreases, which may be due to that the fluidized bed viscosity becomes larger as the normalized bed diameter decreases.

Figure optionsDownload as PowerPoint slideHighlights
► We investigated the float–sink of different sized spheres in a gas–solid fluidized bed at various bed heights.
► The float–sink of smaller sized spheres does not follow the fluidized bed density at higher bed height.
► The float–sink of smaller sized spheres is stabilized by lowering the bed height.
► The stability of the spheres’ float–sink depends on the relationship between the sphere size and the bubble size.