Mixing of powders under periodic shear stress: effect of initial filling level

Abstract

Powder Mixing continues being of great importance in the field of particle technology because of the challenge to get homogeneous mixtures at a large scale. However, it is still moderately understood because of the complexity of designing 3D experiments that consider all the factors affecting the powder flow and powder mixing, hindering the acquisition of enough data that would provide a basic conception of powder behavior. This study involves a simple granular material mixing system of low friction that has five walls, where two of them are high friction moving walls following a cyclic function, and the others are non-friction static walls. The purpose was to create a complete set of 3D experiments of powder distribution to have a better insight into the inside mixing behavior as a function of the initial powder filling level. Experiments at different filling heights were run, obtaining the best mixing at the highest filling level. It was obtained a non-mixing zone with a triangle shape highly affected by the column particle weight. The increase of the vertical component of the resultant force produced by the acrylic motion walls causes a high momentum transfer in the x, y and z directions resulting in a decrease in the no-mixing zone. It was found an asymptotic behavior of the triangle height as a function of the initial filling height of the powders which indicates that values above a limited initial filling level will not have a significant effect on the triangle. A filling height increment of 100 % from 3.81 to 7.62 cm causes an increase in the mixing of 4.44 %. DEM simulations for mixing in the low-shear equipment were run to compare the experimental work