Use of angle of repose and bulk densities for powder characterization and the prediction of minimum fluidization and minimum bubbling velocities

Abstract

The angle of repose (AOR), aerated bulk densities ( ρ A ), and tapped bulk densities ( ρ T ) of 18 fractions of spherical glass beads of mean particle size of 12– 190 μm were studied. The ratio of AOR to ρ A (“weighted” AOR) was found not only to be correlated well with the ratio of ρ T to ρ A , (which is referred to as the Hausner Ratio, HR) for the free-flowing powders, as suggested by Wouters and Geldart (Part. Part. Syst. Characterisation 13 (1996) 254), but also to be able to extend to cover powders showing degrees of cohesiveness. Results of this study suggest that ρ A in the “weighted” AOR could be replaced by ρ T in order to reduce errors caused by the sensitivity of ρ A measurements. The minimum fluidization velocity ( U mf ) and the minimum bubbling velocity ( U mb ) of the powders studied were determined in a cylindrical fluidized bed. The results demonstrated that the ratio of AOR to bulk densities or to HR exhibited a strong exponential decaying characteristics with U mf and U mb with good correlation coefficients. It is believed that U mf and U mb predicted based on the angle of repose and bulk densities are more realistic since the methods for the measurements of AOR and bulk density bear some degrees of “dynamic” aspects of the powders which are responsible for their fluidization behaviour.