Dissipative mass flux and sound wave propagations in monatomic gases

Predicting sound wave dispersion in monatomic gases is a fundamental gas flow problem in rarefied gas dynamics. The Navier‐Stokes‐Fourier model is known to fail where local thermodynamic equilibrium breaks down. Attempts to solve this problem are therefore usually based on the Boltzmann equation. Generally, conventional gas flow models involve equations for mass‐density without a dissipative mass contribution. In this paper we observe that using a dissipative mass flux contribution as a non‐local‐equilibrium correction can improve predictions of sound wave dispersion when compared with experimental data. Two mass dissipation models are investigated: a preliminary model that simply incorporates a diffusive density term in the set of three conservation equations, and another model derived from considering microscopic fluctuations in molecular spatial distributions.