The effective granular temperature based on the fluctuation-dissipation theorem

Dissipative granular systems that are driven continuously by an external forcing, like vertical shaking or fluid flow pulses, exhibit fluid like properties. Different definitions of granular temperature have been proposed for these systems, in analogy to regular fluids of microscopic particles. On the road to creating a setup for measuring both the temperature based on the fluctuation-dissipation theorem TFD and the kinetic temperature Tkin, experiments to measure TFD of a water-fluidized bed of glass beads (d = 250 μm) were performed with a torsion oscillator. For low flow rates around the onset of fluidization, (flow rate Q ∼ 0.30 ml/s) the temperature was on the order of kBTFD ∼ 10−16 J and showed a linear increase with the flow rate. A sharp increase of the damping of the torsion oscillator was found for decreasing flow rates around the onset of fluidization, which can be interpreted as the approach to a glassy regime of the fluidized bed.