Heat Flux in a Granular Gas

TL;DR

This paper investigates the modified Fourier law in granular gases, revealing an additional density-gradient-driven heat flux component and deriving related transport coefficients through theoretical and simulation methods.

Contribution

It introduces a simple physical interpretation of the diffusive heat flux in granular gases and derives the associated transport coefficients, comparing theory with simulations.

Findings

Modified Fourier law with an additional density-gradient term.

Derived expressions for thermal and diffusive heat conductivities.

Good agreement between theoretical predictions and simulation results.

Abstract

A peculiarity of the hydrodynamic Navier-Stokes equations for a granular gas is the modification of the Fourier law, with the presence of an additional contribution to the heat flux that is proportional to the density gradient. Consequently, the constitutive relation involves, in the case of a one-component granular gas, two transport coefficients: the usual (thermal) heat conductivity and a diffusive heat conductivity. A very simple physical interpretation of this effect, in terms of the mean free path and the mean free time is provided. It leads to the modified Fourier law with an expression for the diffusive Fourier coefficient that differs in a factor of the order of unity from the expression obtained by means of the inelastic Boltzmann equation. Also, some aspects of the Chapman-Enskog computation of the new transport coefficients as well as of the comparison between simulation results and theory are discussed.