Granular gas and liquid-gas transition
Coordination : Sébastien Aumaître, CEA Saclay, France
Motivation : The Space Grains WP1 is devoted to the study of the behavior of a granular gas under microgravity. A dissipative granular gas differs from a usual gas of hard spheres due to the inelastic collisions between particles. Continuous injection of energy is thus necessary to sustain a stationary state in this dissipative out-of-equilibrium system. Inelastic collisions are the only interaction mechanism in low-gravity environment. In this working project WP1, we will experimentally study how a granular gas deviates from the quasi-elastic limit (usual gas) when dissipation increases in the system. One way to do that is to increase the volume of the container at a constant particle density all things being equal as it was shown numerically . By varying parameters of the experiment (the number of beads and the volume of the cell), one will try to observe how the granular system deviates or tends to the quasi-elastic limit. Another set of experiments will be devoted to quantify more precisely the clustering transition in order to establish the phase diagram between gas- and solid-like phases and to compare with recent numerical results . Control parameters will be the number of beads, the amplitude and frequency of the forcing, and the moving wall numbers. By means of camera and impact sensors, measurements of the local density of the particles, their velocities, and the force on the confining walls are of primary interest.
 S. Aumaître, A. Alastuey, and S. Fauve, A quasi-elastic regime for vibrated granular gases, Eur. Phys. J B 54, 263 (2006)
 E. Opsomer, F. Ludewig and N. Vandewalle, Phase transitions in vibrated granular systems in microgravity, Phys. Rev. E. 84, 051306 (2011)
 E.Opsomer, F.Ludewig, and N.Vandewalle, Dynamical clustering in driven granular gas,
EPL 99, 40001 (2012)
In the movie below, the color scale is associated to the kinetic energy of the particles. This movie illustrates the injection of energy at the walls, as well as the dissipation of energy in the center of the granular gas.