In the second year of this project, we have continued research into mixing and segregation behaviors in tumblers and shakers. Among the key results are the following.
1. We have determined that different blenders of industrial design share common dynamical behaviors, including
(a) extremely sharp transitions between segregation states, that are observed across wide length scales.
(b) a cut-off size ratio beyond which segregation mechanisms appear to shut down.
The existence of dynamical similarity across length scales (and in different geometries) opens up the possibility to produce new scaling relations for the practical scale-up of blenders of common design. The presence of a cut-off indicates new prospects for designing products to mitigate segregational tendencies.
2. We have identified previously unreported segregation phenomena due to differential particle density in shakers and have begun study of density-induced segregation in tumblers.
3. We have established that particle shape can have a significant effect on blending behavior for coarse grains. In particular,
(a) particles with different shape but nearly identical size and density segregate in tumblers and shakers. Combined shape- and density- variations produce novel and poorly understood effects;
(b) we have identified a new regime of behavior in which shape-induced segregation is reversible -- i.e. particles of different shape can be either mixed or separated at will.
4. We have developed cellular automata models that successfully predict segregation in rotating drums, rocking drums, drums tumbled end-over-end, and V-blender shells.