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DY: Fachverband Dynamik und Statistische Physik

DY 31: Granular matter / contact dynamics II

DY 31.8: Vortrag

Freitag, 30. März 2007, 12:00–12:15, H2

Segregation and convection of granular mixtures in a rotating Hele-Shaw cell at high fill levels — •Frank Rietz and Ralf Stannarius — Otto-von-Guericke Universität Magdeburg, Fakultät für Naturwissenschaften, Institut für Experimentelle Physik, Abteilung Nichtlineare Phänomene

We describe experimentally the segregation and pattern formations in a granular medium that is almost densely packed in a flat container. The experiment is inspired by theoretical work of Awazu [1]. The container is rotated around a horizontal axis at rates of a few rotations per minute. The granulate is a bimodal glass bead mixture. Our experimental results are qualitatively completely different from observations in a loosely packed container, where fluidization of the material leads to the formation of regular segregation stripes, like they are commonly found in rotating drums. Instead, we observe slow convection rolls that are accompanied by and decorated by a segregation of the mixture. 'Conventional' axial stripe patterns are observable for fill levels below 95% tapped volume. At fill levels above 95%, the granulate is nearly jammed and the mobility of particles almost inhibited. Convection modes develop with wave numbers related to cell height. The velocity of these regular convection motion decreases when the initial fill level approaches 100%.

[1] Phys. Rev. Lett. 84, 4585, 2000