  In dense flowing bidisperse particle mixtures varying in size or density
alone, smaller particles sink (driven by percolation) and lighter particles
rise (driven by buoyancy). But when the particle species differ from each other
in both size and density, percolation and buoyancy can either enhance
(large/light and small/heavy) or oppose (large/heavy and small/light) each
other. In the latter case, a local equilibrium condition can exist in which the
two segregation mechanisms balance and particles remain mixed: this allows the
design of minimally-segregating mixtures by specifying particle size ratio,
density ratio, and mixture concentration. Using experimentally validated DEM
simulations, we show that mixtures specified by the methodology remain
relatively well-mixed in the thin rapid surface flows characteristic of heaps
and tumblers commonly used in industry. Furthermore, minimally-segregating
particle mixtures prepared in a fully segregated state in a tumbler mix over
time and eventually reach a state of nearly uniform species concentration.
