Inducing axial banding in bidisperse-by-density granular systems using noncylindrical tumbler geometries

We present evidence of axial banding in rotated, binary granular beds comprising particles of equal size but differing material density. It is demonstrated that the presence of differing particle densities alone may produce limited, localized axial segregation arising due to end-wall effects, but that true axial banding, i.e., axial segregation patterns pervading the full extent of the system may be induced through the use of a rotating tumbler whose internal geometry comprises alternating convex and concave segments. The segregation patterns formed are observed to be stable and reproducible, unlike the unpredictable, metastable banding typically observed in systems containing particles differing in size. Moreover, we demonstrate that, by varying the axial extent and positioning of the individual convex and concave segments, the system geometry may be deliberately tuned in order to directly control both the positions and the widths of the axial bands produced-a finding with significant potential benefits for a range of industrial processes.