(166c) Experimental Verification of Drag Laws for Binary, Gas-Fluidized Systems

Axial species segregation measurements were carried out in a fluidized bed with a binary mixture of Geldart Group B particles. Several bed loadings with glass-polystyrene and polystyrene-polystyrene mixtures were investigated. The experimental results were then compared with MP-PIC numerical simulations with two drag laws for polydisperse systems, following the method described in the companion work by Leboreiro et al. (2006). The first drag law is an ad-hoc extension of a monodisperse drag law; the second one explicitly accounts for the binary nature of the system.

In glass-polystyrene experiments, the polystyrene particles (larger and more massive than the glass ones) act as flotsam; in polystyrene-polystyrene systems the fines act as flotsam. The ad-hoc extension of the monodisperse drag law captures the qualitative segregation profile in the glass-polystyrene systems better, but tends to overpredict the segregation in systems with dissimilar species' concentrations; the binary drag law consistently predicts almost full to full segregation for the corresponding systems. In the case of polystyrene-polystyrene systems, where the species differ only in size, the roles of the two drag laws reverse, with the binary drag law predicting a mild concentration profile and the extended monodisperse drag law predicting full segregation.

The observed discrepancies may be related to differences in bed dynamics between the experimental and simulated systems and/or limitations of the monodisperse drag law. Preliminary results from granular kinetic theory, together with comparisons between the bubbling patterns of the experiments and simulations, are currently being applied to evaluate the relative abilities of the drag laws.