Dynamics of levitated granular materials

Abstract

This diploma thesis deals with the experimental studying of granular gas dynamics. The dissipation of kinetic energy during collision governs the overall dynamical behaviour of a granular gas. Thus some characteristic differences to molecular gas dynamics arise, such as a deviation of the velocity distribution from the Maxwell-Boltzmann distribution, or the spontaneous breaking of the left-right symmetry in a cautiously driven box, that is equally partitioned by an internal barrier. The later phenomenon is often referred to as Maxwell's demon. Yet another consequence of the dissipative nature of granular matter is the formation of cluster states in absence of strong external forces, i.e. a freely evolving granular gas will inevitably "cool" down, that is loose all its kinetic energy. To observe these dissipative processes in granular gases without the overlaying gravitation effect, the gravity of the granular sample has to be balanced. Here, this is experimentally realised by using diamagnetic granular samples that can be levitated in a strong magnetic field. The experimental findings are compared to theoretic predictions, which can, in many cases, be gained from a modified kinetic gas theory or computer simulations. By doing so, it is found that the "cooling" of a freely evolving granular gas is indeed well described by Haff's law, which was first derived 1983 from a modified kinetic gas theory. For the velocity distribution as well good agreements with some predictions made can be found. First attempts to describe the separation in the so called Maxwell's demon experiment theoretically, by solving the equations of motion obtained from the modified kinetic gas theory assuming a number density distribution for granular particles comparable to that of the barometric hight formula, can only partly be true.