Controlling granular segregation using modulated flow

Unsteady flows of granular media are ubiquitous yet remain largely unexplored. In this research, we apply unsteady flows to strongly segregating granular materials to control the segregation pattern and enhance overall mixing. Size-bidisperse granular mixtures with large size ratios flowing onto a quasi-2D bounded heap form stratified layers of large and small particles when the flow rate is modulated. These layers exhibit better average mixing than the segregated patterns generated by steady feed rates. The mechanisms of layer formation under modulated flow differ from those for spontaneous stratification and are related to changes in the composition of the flowing layer at different stages in each feed cycle. The thickness and length of the stratified layers can be controlled by changing the feed rates and feed cycle durations, which is potentially useful for reducing segregation in industrial processes. (C) 2017 Elsevier B.V. All rights reserved.