Remarkable simplicity in the prediction of nonspherical particle segregation

Size-disperse mixtures of noncohesive particles segregate, or demix, during flow. For spherical particles, mixture segregation can be predicted based on the relative particle diameters. However, most particle systems in industry and geophysics involve nonspherical particles. Accounting for the immense range of particle shapes introduces additional parameters. As a proxy for nonspherical particles in general, we perform discrete element method simulations of gravity-driven free-surface flows of bidisperse mixtures of mm-sized particles that vary widely in their size and shape (disks, rods, and spheres). Remarkably, the propensity to segregate, measured in terms of a segregation length scale that characterizes the segregation velocity of the two species, can be predicted based on only the volume ratio of the two particle species. The segregation length scale increases linearly with the log of the volume ratio, as it does for bidisperse mixtures of spherical particles, independent of particle shape.