On the rarefied gas experiments

TL;DR

This paper compares two advanced theories for modeling rarefied gases, analyzing their ability to match experimental data and emphasizing the importance of density-dependent parameters in accurate modeling.

Contribution

It provides a detailed comparison of Rational Extended Thermodynamics and non-equilibrium thermodynamics with internal variables for rarefied gas modeling, highlighting the impact of density dependence.

Findings

Density dependence significantly affects modeling accuracy.

Theories show different capabilities in matching experimental results.

Modeling of rarefied gases requires careful consideration of material parameters.

Abstract

There are limits of validity of classical constitutive laws such as Fourier and Navier-Stokes equations, phenomena beyond those limits have been experimentally found many decades ago. However, it is still not clear what theory would be appropriate to model different non-classical phenomena under different conditions considering either the low-temperature or composite material structure. In this paper, a modeling problem of rarefied gases is addressed. It covers the mass density dependence of material parameters, the scaling properties of different theories and aspects of how to model an experiment. In the following, two frameworks and their properties are discussed. One of them is the kinetic theory based Rational Extended Thermodynamics; the other one is the non-equilibrium thermodynamics with internal variables and current multipliers. In order to compare these theories, an experiment performed by Rhodes is analyzed in detail. It is shown that the density dependence of material parameters has a severe impact on modeling capabilities and can lead to very different results.