Concentration non-uniformity in simple shear flow of cohesive powders

A method is developed to quantify the particle concentration non-uniformity of cohesive powders in a simple shear flow for both dilute and dense condi tions. The ratio of the variance of the particle number concentration, rt, to the square of mean particle number concentration, r = [n'2]/[n](2), is f irst obtained using a series of sub-cells of different volumes based on a d iscrete element simulation of particle dynamics in a simple shear flow. The deviation, ar, of r from the rapid shear rate limit at the same bulk conce ntration is taken as the measure of the particle concentration non-uniformi ty. The effects of shear rates on this concentration non-uniformity are qua ntitatively examined. The quantitative value of this non-uniformity is used to identify a change in the micro-scale cluster structure of dense powder flows under various shear rates and to help in understanding the mechanism for the observed non-monotonic stress-strain rate behavior. (C) 2000 Elsevi er Science S.A. All rights reserved.