Free flowing and cohesive powders agitation in a cylindrical convective blender- kinetics experiments and Markov chain modelling

Université de Toulouse, Centre RAPSODEE, CNRS UMR 5302, Ecole des Mines d’Albi, Campus Jarlard, 81013 Albi Cedex 09, France

^* Corresponding author: mmilhe@mines-albi.fr

Published online: 30 June 2017

Abstract

An original methodology for studying powder flow in a cylindrical convective blender has been developed. A free-flowing and a cohesive powder were studied, at a fixed stirring speed, in rolling regime. For both powders, three apparent flow mechanisms were evidenced: convection in the volume swept by the blades, diffusion/shearing between the agitated zone and the stagnant one, as well as in the stagnant zone itself, and avalanches at the powder bed surface between agitated and stagnant zones. After defining six zones in the blender, tracing experiments were carried out by placing appropriate tracers in different starting zones and sampling the whole bed at different stirring times, which lead to mixing kinetics of the powders into themselves. A Markov chains model of the blender allowed the quantification of the three mechanisms respective magnitude by fitting the experimental data. This simple model has a good agreement with the free-flowing powder data, but is not able to represent well the observations for the cohesive powder. Bed consolidation should probably be taken into account for this kind of powders and thus a linear Markov model is not sufficient.