A recent argon–argon interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation [B. Jager, R. Hellmann, E. Bich, and E. Vogel, Mol. Phys. 107, 2181 (2009); 108, 105 (2010)] was used to calculate the most important thermophysical properties of argon governed by two-body interactions. Second pressure, acoustic, and dielectric virial coefficients as well as viscosity and thermal conductivity in the limit of zero density were computed for natural argon from 83 to 10,000 K. The calculated values for the different thermophysical properties are compared with available experimental data and values computed for other argon–argon potentials. This extensive analysis shows that the proposed potential is superior to all previous ones and that the calculated thermophysical property values are accurate enough to be applied as standard values for the complete temperature range of the calculations.

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Ab initio potential energy curve for the neon atom pair and thermophysical properties for the dilute neon gas. II. Thermophysical properties for low-density neon

Thermal conductivity data for molten metals, published since the review of Touloukian et al. in 1970, are collated and evaluated. Where possible recommended values are given. Where availability of data permits, the Wiedemann-Franz-Lorenz equation relating electrical and thermal conductivities has been assessed. It has been found to be valid for most pure metals at their melting point.

Thermal conductivities of molten metals: Part 1 Pure metals

Transverse thermal conductivity of CFRP laminates: A numerical and experimental validation of approximation formulae

A new reference krypton-krypton interatomic potential energy curve was developed by means of quantum-chemical ab initio calculations for 36 interatomic separations. Highly accurate values for the interaction energies at the complete basis set limit were obtained using the coupled-cluster method with single, double, and perturbative triple excitations as well as t-aug-cc-pV5Z and t-aug-cc-pV6Z basis sets including mid-bond functions, with the 6Z basis set being newly constructed for this study. Higher orders of coupled-cluster terms were considered in a successive scheme up to full quadruple excitations. Core-core and core-valence correlation effects were included. Furthermore, relativistic effects were studied not only at a scalar relativistic level using second-order direct perturbation theory, but also utilizing full four-component and Gaunt-effect computations. An analytical pair potential function was fitted to the interaction energies, which is characterized by a depth of 200.88 K with an estimated standard uncertainty of 0.51 K. Thermophysical properties of low-density krypton were calculated for temperatures up to 5000 K. Second and third virial coefficients were obtained from statistical thermodynamics. Viscosity and thermal conductivity as well as the self-diffusion coefficient were computed using the kinetic theory of gases. The theoretical results are compared with experimental data and with results for other pair potential functions from the literature, especially with those calculated from the recently developed ab initio potential of Waldrop et al. [J. Chem. Phys. 142, 204307 (2015)]. Highly accurate experimental viscosity data indicate that both the present ab initio pair potential and the one of Waldrop et al. can be regarded as reference potentials, even though the quantum-chemical methods and basis sets differ. However, the uncertainties of the present potential and of the derived properties are estimated to be considerably lower.

State-of-the-art ab initio potential energy curve for the krypton atom pair and thermophysical properties of dilute krypton gas.

A four-dimensional potential energy hypersurface (PES) for the interaction of two rigid nitrogen molecules was determined from high-level quantum-chemical ab initio computations. A total of 408 points for 26 distinct angular configurations were calculated utilizing the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory and basis sets up to aug-cc-pV5Z supplemented with bond functions. The calculated interaction energies were extrapolated to the complete basis set limit and complemented by corrections for core–core and core–valence correlations, relativistic effects and higher coupled-cluster levels up to CCSDT(Q). An analytical site–site potential function with five sites per nitrogen molecule was fitted to the interaction energies. The PES was validated by computing second and third pressure virial coefficients as well as shear viscosity and thermal conductivity in the dilute-gas limit. An improved PES was obtained by scaling the CCSDT(Q) corrections for all 408 points by a con...

Ab initio potential energy surface for the nitrogen molecule pair and thermophysical properties of nitrogen gas

A guarded hot-plate apparatus for small circular samples has been developed for the temperature range from −75 to 200‡C. To avoid edge losses, the apparatus is immersed in a liquid whose temperature is a few degrees lower than the mean temperature of the samples. A detailed evaluation procedure with several correction calculations leads to a remaining uncertainty of measurement of 0.5% for measurements on glass samples. This has been confirmed by experiment. Measurements on glass and on insulation material showed that the developed apparatus and the evaluation procedure applied can be used in a relatively wide range of thermal conductivity values (factor 50).

A guarded hot-plate apparatus for thermal conductivity measurements over the temperature range −75 to 200‡C

Air desorbed from the measuring instrument can falsify the thermal conductivity of a gas measured by steady-state methods. For a guarded hot-plate apparatus the contamination effect was determined to depend on both the residence time in the system and the temperature. The investigation covered the gases H2, He, Ne, CH4, N2, air, Ar, and Kr. For gases whose conductivity is better than that of air (H2, He) the measured values are too small, and for gases of poorer conductivity they are too high. Corrections for the effect of impurity have been applied to the measurements presented. These impurity corrections are considerably larger than the precision of the measurements, but they are of the order of the estimated overall uncertainty of the measurements. The departures between the corrected thermal conductivities reported here and values taken from the correlations in the literature run up to 5 % at the highest temperatures.

The thermal conductivity of gases: Incorrect results due to desorbed air

The thermal conductivity of lead (99.99%) has been measured in the range −180 to 500°C using four measuring devices (steady-state method). The thermal conductivity of both solid and liquid lead can be represented as a linear function of the temperature. The uncertainty of the measured values is estimated at 2.5% (solid) and 3% (liquid). Between the melting point and 500°C, the thermal conductivity increases by 14%. The ratio of the thermal conductivity of solid to liquid lead at the melting point corresponds to the ratio of the electric conductivities. The Lorenz function for liquid lead is approximately 1% above the ideal value at the melting point and some 3% lower than the ideal value at 500°C.

W. Hemminger

Papers

A guarded hot-plate apparatus for thermal conductivity measurements over the temperature range −75 to 200‡C

The thermal conductivity of gases: Incorrect results due to desorbed air

Thermal conductivity of lead in the range -180 to 500°C