Granular flow

Effective temperature in a vibrated granular medium


Effective temperature in a vibrated granular medium

        The flow state of granular system can be tuned by increasing vibration intensity from closing to the jamming state to a dense flow. The motion of tracking particles are analyzed using ultra-fast synchrotron X-ray imaging techniques. The viscosity and diffusion constant are calculated, and the effective temperature is hereafter derived using the fluctuation-dissipation theorem. It is demonstrated that the relaxation time increases rapidly as the system approaches the jamming transition. The characteristic energy scale obtained using Arrhenius fitting in our system is consistent with previous works on hard sphere model, suggesting that the relaxation process in granular system is taken place by creating free volume against external pressure. The work has been published on Soft Matter 10, 5398 (2014).  ( PDF )

Figure: X-ray projection images of the tracers inside the acrylic container filled with glass beads before (a) and after (b) the extended period of vibration. (c) Schematic of the experimental setup. The granular medium in the container develops a strong surface tilting and convection. Two intruder particles are placed near the corner which as the largest surface height H. (d) Effective temperature versus vibration intensity. (inset) The normalized structural relaxation time as a function of nor