THE STRUCTURE OF MIXTURES OF PARTICLES GENERATED BY TIME-DEPENDENT FLOWS

A computer-controlled mixing apparatus has been used to investigate the mixing of glass beads in a cylindrical vessel rotating about its axis and rocking in the vertical direction. The structures of mixtures generated in these experiments are preserved in an undisturbed state using a solidification technique. Experiments show that the motion of particles is strongly affected by end-wall effects. Mixing patterns at internal cross-sections differ significantly from patterns observed at end walls, indicating that observations at exposed surfaces are not representative of mixing processes inside the powder bed. Solidified structures are also used to compare the mixing effectiveness of different motion protocols such as varying the number of revolutions and rocking frequency. Structures generated solely by steady rotational motion exhibit very slow mixing while structures produced with simultaneous rotational and rocking motions reveal that significant mixing enhancements can be achieved when the time-periodicity of the rotational and rocking flows is disrupted.