Rational Extended Thermodynamics of a Rarefied Polyatomic Gas with Molecular Relaxation Processes

TL;DR

This paper refines rational extended thermodynamics for rarefied polyatomic gases by individually modeling molecular relaxation processes, using a triple hierarchy of moments and maximum entropy closure, and validates ultrasonic wave dispersion predictions with experimental data.

Contribution

It introduces a detailed thermodynamic model with a triple hierarchy of moments and new production terms, enhancing the understanding of molecular relaxation in polyatomic gases.

Findings

Dispersion relation predictions match experimental data for CO2, Cl2, and Br2.

The model effectively captures rotational and vibrational relaxation processes.

The ET7 theory provides a comprehensive framework for ultrasonic wave analysis.

Abstract

We present a more refined version of rational extended thermodynamics of rarefied polyatomic gases in which molecular rotational and vibrational relaxation processes are treated individually. In this case we need a triple hierarchy of the moment system and the system of balance equations is closed via the maximum entropy principle. Three different types of the production terms in the system, which are suggested by a generalized BGK-type collision term in the Boltzmann equation, are adopted. In particular, the rational extended thermodynamic theory with seven independent fields (ET7) is analyzed in detail. Finally, the dispersion relation of ultrasonic wave derived from the ET7 theory is confirmed by the experimental data for CO2, Cl2, and Br2 gases.