Non-Equilibrium Reacting Gas Flows

The exchange of momentum and energy in gas flows through microchannels is significantly influenced by the gas-surface interaction. At this scale often the gas is rarefied and therefore non-equilibrium effects in the fluid flow can arise in a layer which extends for a distance equivalent to the mean free path from the walls. Typical examples of non-equilibrium phenomena for rarefied gas flows are slip at the wall, thermal transpiration and temperature jump at the wall. The aim of the present study is to experimentally investigate the non-equilibrium effects present in an isothermal pressure induced flow for a large range of rarefaction conditions. The isothermal slip at the wall is usually characterized by the tangential momentum accommodation coefficient (TMAC). This coefficient depends on the molecular nature of the gas and on the physical characteristics of the surface, such as material and roughness. In particular this paper explores the influence of the surface material on the TMAC through measurements of the mass flow rate in capillaries for the special case of nitrogen. Commercially available microtubes of three different metallic materials — stainless steel, copper, and brass — were considered in the analysis. Measurements were performed with a dynamic measurement technique based on the constant volume method and comprehend the transitional flow regime and most part of the slip regime. Theoretical results obtained from the solution of the Boltzmann equation via the BGK kinetic model, which is a simplified approximation for the collisional term, were compared to the experimental results.

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Computational framework for the regularized 20-moment equations for non-equilibrium gas flows

International Journal for Numerical Methods in Fluids ◽

10.1002/fld.1747 ◽

2008 ◽

Vol 56 (8) ◽

pp. 1433-1439 ◽

Cited By ~ 5

Author(s):

S. Mizzi ◽

X. J. Gu ◽

D. R. Emerson ◽

R. W. Barber ◽

J. M. Reese

Keyword(s):

Gas Flows ◽

Moment Equations ◽

Computational Framework ◽

Non Equilibrium

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Analysis of Rotational Non-equilibrium in Rarefied Gas Flows by REMPI

The proceedings of the JSME annual meeting ◽

10.1299/jsmemecjo.2004.7.0_35 ◽

2004 ◽

Vol 2004.7 (0) ◽

pp. 35-36

Author(s):

Hideo MORI ◽

Tomohide NIIMI ◽

Isao AKIYAMA ◽

Takumi TSUZUKI

Keyword(s):

Rarefied Gas ◽

Gas Flows ◽

Rarefied Gas Flows ◽

Non Equilibrium

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A modular particle–continuum numerical method for hypersonic non-equilibrium gas flows

Journal of Computational Physics ◽

10.1016/j.jcp.2007.01.022 ◽

2007 ◽

Vol 225 (1) ◽

pp. 1159-1174 ◽

Cited By ~ 107

Author(s):

T.E. Schwartzentruber ◽

L.C. Scalabrin ◽

I.D. Boyd

Keyword(s):

Numerical Method ◽

Gas Flows ◽

Non Equilibrium

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On Singular Closures for the 5-Moment System in Kinetic Gas Theory

Communications in Computational Physics ◽

10.4208/cicp.201213.130814a ◽

2015 ◽

Vol 17 (2) ◽

pp. 371-400 ◽

Cited By ~ 12

Author(s):

Roman Pascal Schaerer ◽

Manuel Torrilhon

Keyword(s):

Maximum Entropy ◽

Maximum Entropy Principle ◽

Second Order ◽

Gas Flows ◽

Moment Equations ◽

Moment System ◽

Entropy Principle ◽

Kinetic Gas Theory ◽

Closure Theory ◽

Non Equilibrium

AbstractMoment equations provide a flexible framework for the approximation of the Boltzmann equation in kinetic gas theory. While moments up to second order are sufficient for the description of equilibrium processes, the inclusion of higher order moments, such as the heat flux vector, extends the validity of the Euler equations to non-equilibrium gas flows in a natural way.Unfortunately, the classical closure theory proposed by Grad leads to moment equations, which suffer not only from a restricted hyperbolicity region but are also affected by non-physical sub-shocks in the continuous shock-structure problem if the shock velocity exceeds a critical value. Amore recently suggested closure theory based on the maximum entropy principle yields symmetric hyperbolic moment equations. However, if moments higher than second order are included, the computational demand of this closure can be overwhelming. Additionally, it was shown for the 5-moment system that the closing flux becomes singular on a subset of moments including the equilibrium state.Motivated by recent promising results of closed-form, singular closures based on the maximum entropy approach, we study regularized singular closures that become singular on a subset of moments when the regularizing terms are removed. In order to study some implications of singular closures, we use a recently proposed explicit closure for the 5-moment equations. We show that this closure theory results in a hyperbolic system that can mitigate the problem of sub-shocks independent of the shock wave velocity and handle strongly non-equilibrium gas flows.

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