Calculation of the thermal conductivity of low-density CH4–N2 gas mixtures using an improved kinetic theory approach

Abstract

The thermal conductivity of low-density CH 4 -N 2 gas mixtures has been calculated by means of the classical trajectory method using state-of-the-art intermolecular potential energy surfaces for the CH 4 -CH 4 , N 2 -N 2 , and CH 4 -N 2 interactions. Results are reported in the temperature range from 70 K to 1200 K. Since the thermal conductivity is influenced by the vibrational degrees of freedom of the molecules, which are not included in the rigid-rotor classical trajectory computations, a new correction scheme to account for vibrational degrees of freedom in a dilute gas mixture is presented.The calculations show that the vibrational contribution at the highest temperature studied amounts to 46% of the total thermal conductivity of an equimolar mixture compared to 13% for pure nitrogen and 58% for pure methane. The agreement with the available experimental thermal conductivity data at room temperature is good, within ±1.4%, whereas at higher temperatures larger deviations up to 4.5% are observed, which can be tentatively attributed to deteriorating performance of the measuring technique employed. Results are also reported for the magnitude and temperature dependence of the rotational collision number, Z rot , for CH 4 relaxing in collisions with N 2 and N 2 relaxing in collisions with CH 4 . Both collision numbers increase with temperature, with the former being consistently about twice the value of the latter.

Cross second virial coefficients and dilute gas transport properties of the (CH 4 + CO 2 ), (CH 4 + H 2 S), and (H 2 S + CO 2 ) systems from accurate intermolecular potential energy surfaces

“…The transport properties of dilute gas mixtures can be calculated using the kinetic theory of polyatomic gases [8,14,[24][25][26][38][39][40][41][42]. For each transport coefficient, a system of linear equations needs to be solved.…”

“…The approaches employed in the present work for the calculation of the shear viscosity η, the thermal conductivity λ (under steadystate conditions, see reference [8] for details), and the product of the molar density and the binary diffusion coefficient, ρ m D, are the same as in our studies of the (CH 4 + N 2 ) system [8,14]. For completeness, we present the approach for viscosity here and refer the reader to references [14] and [8] for the details concerning the other two transport properties. We note that there is an error in the final expression for the mixture viscosity in reference [14].…”

“…The macroscopic properties of a dilute gas are governed by binary molecular interactions, and the recent computational advances in the field have allowed us not only to accurately determine the intermolecular potential energy surfaces (PESs) using quantum-chemical ab initio methods [3][4][5][6], but also to calculate the transport properties by making use of a rigorous molecular description [7,8]. Such calculations have been performed for a number of simple gases, such as methane [9,10], carbon dioxide [5], hydrogen sulfide [4,11], water vapor [12,13], or ethylene oxide [6], yielding transport property values with an uncertainty commensurate with the best experimental measurements over wide temperature ranges.…”

“…Such calculations have been performed for a number of simple gases, such as methane [9,10], carbon dioxide [5], hydrogen sulfide [4,11], water vapor [12,13], or ethylene oxide [6], yielding transport property values with an uncertainty commensurate with the best experimental measurements over wide temperature ranges. We have recently extended the calculations to binary mixtures and have reported values for three traditional transport properties (viscosity, thermal conductivity, binary diffusion coefficient) and for the cross second virial coefficient of (CH 4 + N 2 ) mixtures [8,14]. The objective of this paper is to extend the study to include (CH 4 + CO 2 ), (CH 4 + H 2 S), and (H 2 S + CO 2 ) mixtures.…”

“…To account for quantum effects semiclassically, the quadratic Feynman-Hibbs (QFH) effective pair potential [23] was utilized. Transport properties in the dilute gas limit have been determined by means of the classical trajectory approach in conjunction with the kinetic theory of molecular gases [8,14,[24][25][26]. The accuracy and usefulness of this approach has been demonstrated for several pure molecular gases and gas mixtures, see, for example, references [5][6][7][8][12][13][14].…”