Dresden 2014 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 22: Slow Dynamics in Glasses and Granular Matter I (Joint Focus Session with DY and CPP)

DF 22.9: Vortrag

Donnerstag, 3. April 2014, 12:15–12:30, HÜL 186

Slow convection in densely packed granular mixtures — •Frank Rietz and Ralf Stannarius — University of Magdeburg, Institute of Experimental Physics, Department of Nonlinear Phenomena

Handling of granulate in partly filled rotating containers is a common situation in industrial processes. Contrary to ensembles of loosely packed grains, the container can be filled so dense that fluidization is limited to a shallow surface layer. Then, the deeper layers are in a locked state, only creeping motions on longer time scales are possible.

We study such a situation in a flat rotating container of aspect ratio 1 that is almost completely filled with a bidisperse mixture. Irrespective of the limited mobility of the grains we observe nonuniform segregation patterns accompanied by slow convective motion. Many features of the convection flow amplitude, like regular oscillatory modulations of the convection velocity, cessations and spontaneous reversals of the circulation are comparable to convection in ordinary liquids at high Rayleigh numbers, in geometries with aspect ratio 1.

[1] F. Rietz & R. Stannarius, Phys. Rev. Lett. 108, 118001 (2012).