Title: Dynamics and Structure in a Uniformly Heated Granular Fluid

Author (Poster): Rohit Ingale, Pall Life Sciences

Abstract:

We report an experimental study of the velocity distributions and structure of a quasi-2D uniformly heated granular fluid over a wide range of densities and experimental parameters. We generate a uniformly heated granular fluid by vertically vibrating an ensemble of monodisperse spheres (diameter $D =1.191mm$) confined between two horizontal glass plates separated by $1.6D$, thus ensuring a quasi-2D configuration. The horizontal arrangement and strong vibrational forcing, suppress the effects of gravity, allowing us to study a wide range of filling fractions. The driving bottom plate is chosen to be a rough glass disk, which upon vibration, efficiently randomizes the trajectories of individual particles and minimizes gravity induced rolling. We follow a statistical mechanics approach to study the particle velocity distributions, over a wide range of filling fraction and vibration parameters (frequency and amplitude). In agreement with previous studies, we find a consistent overpopulation in the distribution's high energy tails. Moreover, we calculate the particle velocity deviations from Maxwell-Boltzmann distribution and find it to be well described by a 4th-order polynomial. We also study the crystallization transition, of the quasi-2D granular fluid, which is accompanied by certain structural changes in the fluid. We quantify these structural changes using Voronoi tessellation accompanied by a certain shape factor (ratio of circumference squared to surface area of Voronoi polygons). The shape factor analysis provides a clear physical picture of competition between less and more ordered domains and of gradual building of a regular hexagonal arrangement in the region of phase transition. In general, the results of our experimental study provide a much deeper understanding of physics of granular materials.