Measurement of the Drag on Spheres Moving through Gaseous Fluidized Beds

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Abstract
Certain substances float on the surfaces of gaseous fluidized beds and others sink. This phenomenon has industrial applications in separation by creaming and sedimentation. To help the development of these applications the author measured the drag on metallic spheres falling through various fluidized beds of glass beads and certain granular powders. The meta***llic spheres were attached to a nylon thread which passed over a pulley system. Different balance weights were attached to the other end of the thread to produce different uniform velocities of fall. The friction of the system and the buoyancy of the immersed metallic spheres were predetermined. The drag on the sphere was then the only unknown. It was found that the drag is a function of three dimensionless groups, namely Reynolds number, Froude number and the ratio of the diameter of the metallic spheres to the mean diameter of the glass beads or powders forming the fluidized beds. For spheres above a certain diameter deviation occurred in the measurement of the drag owing to wall effect.

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