  In bidisperse particle mixtures varying in size or density alone, large
particles rise (driven by percolation) and heavy particles sink (driven by
buoyancy). When the two particle species differ from each other in both size
and density, the two segregation mechanisms either enhance (large/light and
small/heavy) or oppose (large/heavy and small/light) each other. In the latter
case, an equilibrium condition exists in which the two segregation mechanisms
balance and the particles no longer segregate. This leads to a methodology to
design non-segregating particle mixtures by specifying particle size ratio,
density ratio, and mixture concentration to achieve the equilibrium condition.
Using DEM simulations of quasi-2D bounded heap flow, we show that segregation
is significantly reduced for particle mixtures near the equilibrium condition.
In addition, the rise-sink transition for a range of particle size and density
ratios matches the combined size and density segregation model predictions.
