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On the Rarefied Gas Experiments

Department of Energy Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and Economics (BME), 1111 Budapest, Hungary
Department of Theoretical Physics, Wigner Research Centre for Physics, Institute for Particle and Nuclear Physics, 1121 Budapest, Hungary
Montavid Thermodynamic Research Group, 1112 Budapest, Hungary
Entropy 2019, 21(7), 718;
Received: 6 July 2019 / Revised: 20 July 2019 / Accepted: 22 July 2019 / Published: 23 July 2019
(This article belongs to the Special Issue Entropy and Non-Equilibrium Statistical Mechanics)
PDF [597 KB, uploaded 23 July 2019]


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. The discussion 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 presented. 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 on sound speed in rarefied gases at high frequencies, performed by Rhodes, is analyzed in detail. It is shown that the density dependence of material parameters could have a severe impact on modeling capabilities and influences the scaling properties. View Full-Text
Keywords: rarefied gases; non-equilibrium thermodynamics; kinetic theory rarefied gases; non-equilibrium thermodynamics; kinetic theory

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Kovács, R. On the Rarefied Gas Experiments. Entropy 2019, 21, 718.

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