Granular segregation in the double-cone blender: Transitions and mechanisms

We investigate granular segregation in one of the most common industrial de vices used in granular processing: the double-cone blender. We report sever al new and spontaneously occurring segregation patterns, including stripes, bands, and a symmetry-breaking state in which one species vacates half the tumbler. By varying the tumbling speed along with particle size and size r atio, we find that the transitions between segregated patterns are extremel y sharp: Changes in fill level or speed of under one percent are sufficient to produce a reproducible qualitative change in the observed pattern. We s how that the several distinct segregation patterns observed experimentally can be reproduced from a simplified model in which outward rolling on the c onvective granular cascade competes against inertial motion of rapidly movi ng large particles. Finally, we identify a cutoff particle size ratio above which large particles become buried in the cascading flow, and segregation appears to cease. (C) 2001 American Institute of Physics.