Models of fluidized granular materials: examples of non-equilibrium stationary states

TL;DR

This paper reviews models of fluidized granular materials under various external forces, highlighting their non-equilibrium stationary states, density correlations, and the role of granular temperature in these systems.

Contribution

It provides a comparative overview of different models of granular materials under external forcing, emphasizing the significance of granular temperature in non-equilibrium stationary states.

Findings

Granular temperature differs from the bath temperature in driven systems.

Mixed granular materials can have different stationary temperatures.

Granular temperature influences escape times in potential wells.

Abstract

We review some models of granular materials fluidized by means of external forces such as: random homogeneous forcing with damping, vibrating plates, flow in an inclined channel and flow in a double well potential. All these systems show the presence of density correlations and non-Gaussian velocity distributions. These models are useful to understand the role of a kinetically defined ``temperature'' (in this case the so-called {\em granular temperature}) in a non-equilibrium stationary state. In the homogeneously randomly driven gas the granular temperature is {\em different} from that of the driving bath. Moreover two different granular materials mixed together may stay in a stationary state with different temperatures. At the same time, granular temperature determines (as in equilibrium systems) the escape time from a well in a double well potential.