Frank Rietz Department for Nonlinear Phenomena Otto von Guericke-University Magdeburg, Germany phone: +49-(0)391-6718528

Nonlinear Phenomena group Biophysics group

Department for Natural Sciences University Magdeburg

Convection rolls in almost densely filled rotating containers

Segregation and pattern formations in a granular medium that is almost densely packed in a flat container is experimentally demonstrated. The experiment is inspired by theoretical work of Awazu [Phys. Rev. Lett. 84, 4585 (2000)]. A flat transparent container is rotated around a horizontal axis at rates of a few rotations per minute. The granulate is a bimodal glass bead mixture. The 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, slow convection rolls that are accompanied by, and decorated by, a segregation of the mixture have been observed. In nearly filled cells, the granulate is on the brink of jamming and the mobility of particles almost inhibited. Convection modes develop with wave numbers related to cell height. Nonetheless, 'conventional' axial stripe patterns are also observable if the filling level of the container is below some critical value. In such cases the granulate exhibits a chute flow.
Although there are some superficial similarities to well known convection in vibrated granular systems there are striking differences concerning driving forces, segregation patterns, and number of rolls. Our system complements convection phenomena found in agitated granulates.

Movie in better quality (12MB) click here.

Research Highlight
Nature 452, 4 (2008).

A demonstration movie of the preparation of the experiment is available here.

4 rolls in a rotating container, experimental data (anim. gif)
dark/bright: enriched with small/large beads
(real time 16 hrs, 16cm x 4cm x 0.5cm)

sketch of the rotating flat container:
(measurements for movies below)

In order to construct a movie the cell is stopped every 20 rotations at vertical position (as shown in the figure above) and a picture is taken from the front side. For an impression you may download high resolution movies or play low resolution flash movies. These videos show the coarsening of axial stripe pattern (movie 1) and the evolution of convective flow patterns (movies 2-4). The container height is 8 cm and rotational speed 20 rotations per minute. Dark areas in movies indicate domination of small particles, light areas indicate domination of large particles.

Download of high resolution mpeg1 movies

Movie 1 (right click) chute flow regime, axial segregation
size: 28 MB; length: 33 s; time lapse: factor 1,800
total 20,000 rotations; maximum flow speed: 500 µm per rotation

Movie 2 (right click) convection regime, cluster motion
size: 35 MB; length: 42 s; time lapse: factor 1,800
total 25,200 rotations; maximum cluster speed: 40 µm per rotation

Movie 3 (right click) faster version of movie 2
size: 7 MB; length: 8 s, time lapse: factor 9,000
total 25,200 rotations; maximum cluster speed: 40 µm per rotation

Movie 4 (right click) coloured version of movie 2; top: movie 2, centre: vertical velocity component (red=upwards; blue=downwards), bottom: horizontal velocity component (red=right, blue=left)
size: 35 MB, length: 42 s, time lapse: factor 1,800
total 25,200 rotations; maximum cluster speed: 40 µm per rotation

You can also play these movies in lower resolution
(current version of Adobe Flash Player required, download here ≈1 MB)

Demonstration movie of the experiment

Tilo Finger, Andreas Voigt, Jörg Stadler, Heiko G. Niessen, Lama Naji, and Ralf Stannarius
Coarsening of axial segregation patterns of slurries in a horizontally rotating drum
Phys. Rev. E. 74, 031312 (2006). 

Tilo Finger and Ralf Stannarius
Influences of the interstitial liquid on segregation patterns of granular slurries in a rotating drum
Phys. Rev. E. 75, 031308 (2007).