Collective phenomena in vertically shaken granular matter
This project focuses on phase transitions which occur in vertically shaken granular matter. In analogy with classical physics, studying the statistics of such systems at and close to critical points will help the understanding of the nature of the transitions and answer the question if and how the granular hydrodynamic approach breaks down.
The first example of such a transition is the granular Leidenfrost effect which is observed in an experiment with a quasi-2D container filled with glass beads (see Figure 1). The setup is vibrated vertically using our powerful shaker up to an acceleration equivalent to 90g and analyzed using images recorded with a high-speed camera. We find that for a sufficiently large number of particle-layers and above a critical shaking strength a density-inverted state is reached in which the density near the bottom is distinctively lower than above: A dense cluster of beads with an almost perfect hexagonal close packing is elevated and supported by a few fast particles underneath the cluster. This is reminiscent of the original Leidenfrost effect where a water droplet hovers on top of a vapor layer over a hot plate.
When the shaking is sufficiently strong, granular convection rolls are formed from the granular Leidenfrost state (Figure 2). A group of particles picks up an excess of energy from the vibrating bottom and collectively moves upward. A downward motion of neighboring particles balanced the upward motion leading to the formation of a convection roll.
Figure 1: In 1756 Johann Gottlob Leidenfrost first discovered that a drop of water on a red-hot spoon floats on its own vapor layer. The effect occurs above a critical temperature of 220°C. The drop survives for an astonishingly long time (easily exceeding a minute), because the vapor-cushion prevents direct heat transfer from the hot surface to the droplet. The granular version of the Leidenfrost effect can be observed in an experiment with a quasi-2D container filled with glass beads.
Figure 2: Convection rolls in vertically shaken granular matter
Info: Devaraj van der Meer
Researchers: Sylvain Joubaud, Peter Eshuis, Detlef Lohse, Ko van der Weele, Devaraj van der Meer.
Collaborators: Stefan Luding (MSM UTwente), Peter Reimann (Universität Bielefeld)