Introduction. The Classical Geldart’s Diagram and the New Type of Gas-Fluidization Behavior
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A typical fluidized bed consists of a vertical vessel closed at the bottom by a porous plate on which a bed of particles is resting. A fluid is supplied to the powder bed from below. At sufficiently high gas flow, the gas pressure drop balances the material weight per unit area and the bed expands in the so-called fluidized state. Traditionally, fine particles were impossible to fluidize by gas due to their strongly cohesive behavior. However, a new class of powders has arisen in the last few years that can be uniformly fluidized in a nonbubbling fluid-like state. Fine particles in these special powders aggregate according to a dynamic aggregation process, which ends up with the formation of porous light aggregates that can be fluidized by a gas, much like coarse beads are fluidized by a liquid. In this chapter, the classical Geldart diagram and the newly-reported fluid-like behavior exhibited by this special class of fine powders are reviewed.
KeywordsFumed Silica Atomic Layer Deposition Fluidization Behavior Minimum Fluidization Interparticle Force
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