Reverse segregation in inclined chute flows of broadly bidisperse granular mixtures

Size-induced segregation in granular flows of narrowly bidisperse mixtures has been studied extensively, but questions remain about segregation behavior in the regime where the forces driving segregation of the larger species are weak compared to gravity. In the normal segregation scenario for stable inclined chute flows of bidisperse mixtures, segregation forces drive large particles towards the free surface, forming a large particle domain atop the small - if secondary flows are suppressed. Beyond a threshold large-to-small size ratio of roughly 3:1, gravity is expected to overpower segregation forces, causing the large particles to sink. To explore the broadly bidisperse limit, we perform discrete element method simulations considering size ratios of up to 8:1. Computed steady-state flow profiles indicate that depending on the size ratio and relative mass concentration of the larger species, several intriguing behaviors are apparent, including reverse segregation and a tendency to form alternating large and small particle layers along the vorticity direction, with layer thickness set by the large particle size.



Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.