(421q) Examination of Mixing and Segregation Regions in Three Dimensional Granular Tumbler Flow Using Subsurface X-Ray Visualization

Granular mixing in rotating tumblers is often plagued by flow induced segregation due to differences in particle size or density. The mixing and segregation behavior are connected to geometrical effects of the tumbling protocol and tumbler shape, which can be captured by modeling the flow as a continuum dynamical system. To better understand granular mixing, we study blinking spherical tumbler (BST) flow in which a partially-filled spherical tumbler is rotated sequentially about two axes by angles up to 180 degrees. Though the BST flow is a simple three-dimensional flow, it is predicted to exhibit two specific behaviors based on the dynamical systems model: persistent barriers to mixing (KAM tubes) occur in regions that surround curves of elliptic periodic points, while mixing occurs more readily in regions that surround curves of hyperbolic periodic points.  To test the validity of the dynamical systems model, we measure, using X-ray subsurface imaging, the location of X-ray opaque tracer particles in a bed of X-ray transparent particles. Displacements of particles within hyperbolic mixing regions and the elliptic KAM regions are compared to the dynamical systems predictions.  Ultimately, a dynamical systems perspective has potential to better inform mixing strategies for 3D tumbled granular flow. Funded by NSF Grant CMMI-1000469.