Coarsening of axial segregation patterns of slurries in a horizontally rotating drum

Abstract

Segregation structures of granular mixtures in rotating drums represent classical examples of pattern formation in granular material. We investigate the coarsening of axial segregation patterns of slurries in a long horizontally rotating cylinder. The dynamics and the three-dimensional geometry of the segregation structures are analyzed with optical methods and nuclear magnetic resonance imaging. Previous studies have mainly considered global statistical features of the pattern dynamics. In order to get insight into driving mechanisms for the coarsening process, we focus on the details of the dissolution of individual bands. We treat the coarsening as a consequence of interactions of adjacent bands in the pattern, which are determined by their geometrical relations. In addition to initially homogeneous mixtures, which evolve to spontaneously formed patterns, we study the evolution of specially prepared simple initial states. The role of the three-dimensional geometry of the axial core in the dissolution process of segregation bands is demonstrated. Relations between geometry and dynamic processes are established, which may help to find the correct microscopic models for the coarsening mechanism.

Granular materials composed of shape-anisotropic grains

“…There are several common methods used to characterize grain ensembles, irrespective of grain shapes. Modern experimental tools like X-ray Computed Tomography (X-ray CT) or Magnetic Resonance Imaging (MRI) are increasingly used for characterizing not only coarse grain packing [24][25][26], but also local packing structures and orientation at the grain level [27][28][29]. Grain sizes accessible with X-ray CT equipment range from several micrometers [30] to centimeters [28].…”

“…MRI, on the other hand, requires the presence of liquids containing NMR sensitive nuclei, the most abundant ones being protons. In order to employ this method for the analysis of granular beds, one is either restricted to NMR sensitive grains like seeds [24] or pharmaceutic pills, or one has to study solid particles immersed in a liquid [26]. One can mark and trace particles with appropriate radio frequency and magnetic field gradient pulse sequences [31].…”

Radial and axial segregation of granular matter in a rotating cylinder: A simulation study

“…During the latter portion of the run, extending over more than half its total length, there is no suggestion of further pattern change. Band coarsening is a well-known experimental result, with the band count falling roughly logarithmically with time [20], although the dependence can be more complicated than this [22].…”

“…An alternative perspective is provided by systems that begin in an axially segregated state, a problem also studied experimentally with MRI [22,37]. Various scenarios exist, of which preserving the original state and axial mixing represent two extremes, while rearrangement into some other band pattern is also a possibility.…”

Motor-Mediated Microtubule Self-Organization in Dilute and Semi-Dilute Filament Solutions

“…Likewise, in [11], the authors find slow coarsening when studying the dynamics of slurries in circular and square tubes. When studied in complex, higher dimensional geometries, bands of segregated material have been known to exhibit slow coarsening but with more complicated dynamics [12]. Long term bundle formation is known to occur in liquid crystal systems as well; however, ordering in such systems is due mostly to thermodynamic considerations as opposed to active motor mediated effects [9].…”