V. Vesovic

The prediction of the viscosity of dense gas mixtures

An extension of an earlier procedure for the evaluation of the viscosity of very dense gas mixtures is proposed. The scheme is based upon the rigid-sphere theory of dense fluids, which is modified to take into account the behavior of real gases in a self-consistent manner. In particular, it is shown that a pseudoradial distribution function for each pure gas constructed from pure component viscosity data is a smooth function of density and is well behaved in limits of both high and low density. The method proposed removes the restrictions on the range of applicability of earlier methods. Comparisons with the limited amount of experimental information available indicate that the procedure allows evaluation of the viscosity of gas mixtures to within a few percent.

On the validity of the simplified expression for the thermal conductivity of Thijsse et al.

The simplified expression for the thermal conductivity of polyatomic gases originally proposed by Beenakker and co-workers has been tested above 300 K. Using recent experimental and correlated results it has been found that a very good representation of the experimentally determined thermal conductivity coefficients can be achieved when this simple formula, eq. (20) in text, is applied to N2, CO, CO2,, CH4 and CF4. Additional results for the coupling cross-section (10E10D) point to an inadequacy of the Mason-Monchick approximation.

Viscosity of Natural-Gas Mixtures: Measurements and Prediction

New measurements of the viscosity of a natural-gas mixture are reported. The measurements were performed in a vibrating-wire viscometer, in the temperature range from 313 to 455 K at a pressure close to atmospheric and in the temperature range from 240 to 353 K at pressures up to 15 MPa. The uncertainty of the reported measurements is estimated to be ±1%. The data were employed to validate further an existing method of predicting the viscosity of mixtures at high pressures.

The transport properties of ethane. I: Viscosity

A new representation of the viscosity of ethane is presented. The representative equations are based upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory in the zero-density limit, vapor phase, and critical region. The representation extends over the temperature range from 100 K to the critical temperature in the liquid phase and from 200 K to the critical temperature in the vapor phase. In the supercritical region, the temperature range extends to 1000 K for pressures up to 2 MPa and to 500 K for pressures up to 60 MPa. The ascribed accuracy of the representation varies according to the thermodynamic state from ±0.5 % for the viscosity of the dilute gas near room temperature to ±3.0% for the viscosity at high pressures and temperatures. Tables of the viscosity, generated by the relevant equations, at selected temperatures and pressures and along the saturation line, are also provided.

Predicting the viscosity of natural gas

The viscosity of natural gas has been evaluated by four methods: the Lohrentz–Bray–Clark (LBC), Pedersen et al. (PFCT), SUPERTRAPP, and Vesovic–Wakeham (VW) methods. The predictions have been compared with available experimental data that cover the temperature range from 240 to 444 K and pressures up to 55 MPa. The PFCT and VW methods showed the smallest rms deviations, while the predictions of SUPERTRAPP were only marginally worse. The results indicate that these three methods are capable of predicting the viscosity of natural gas with an rms deviation of 3% and maximum deviations of 5 to 6%. The LBC method proved less reliable with maximum deviations of 8 to 9%.

The transport properties of ethane. II: Thermal conductivity

A new representation of the thermal conductivity of ethane is presented. The representative equations are based upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory in the zero-density limit and in the critical region. The representation extends over the temperature range from 100 K to the critical temperature in the liquid phase and from 225 K to the critical temperature in the vapor phase. In the supercritical region the temperature range extends to 1000 K for pressures up to 1 MPa and to 625 K for pressures up to 70 MPa. The ascribed accuracy of the representation varies according to the thermodynamic state from ±2% for the thermal conductivity of the dilute gas near room temperature to ±5% for the thermal conductivity at high pressures and temperatures. Tables of the thermal conductivity, generated by the relevant equations, at selected temperatures and pressures and along the saturation line are also provided.

Alternative expressions for the thermal conductivity of dilute gas mixtures

New expressions for the thermal conductivity of a multicomponent mixture of polyatomic gases have been derived within the semi-classical Wang Chang-Uhlenbeck kinetic theory. Using the Wang Chang-Uhlenbeck formulation of the solution of the kinetic equations, the thermal conductivity is written explicitly, to an arbitrary order of approximation, in terms of a series of effective cross-sections for the first time and in a form suitable for computer implementation. In the alternative formulation of Thijsse, t Hooft, Combe, Knaap and Beenakker, the thermal conductivity of the mixture is also written explicitly in terms of the effective cross-section. The resulting expression proves to be much simpler than hitherto available.

Thermal conductivity of multicomponent polyatomic dilute gas mixtures

A new expression for the thermal conductivity of anN-component polyatomic gas mixture in the dilute-gas limit has been derived, based on the Thijsse approximation. The results are presented in terms of experimentally accessible quantities to allow for easier calculation of the thermal conductivity and easier interpretation of the experimentally available data. The resulting expression are much simpler than other formulae hitherto available. An additional new expression for the thermal conductivity of anN-component polyatomic gas mixture has been derived by replacing the effective cross-section by their spherical limits. These results are cast in a form which is analogous with, and no more complicated than, the corresponding expressions for purely monatomic mixtures.

Practical, accurate expressions for the thermal conductivity of atom-diatom gas mixtures

The use of an expansion vector based upon the total energy flux has led to a considerable simplification of the kinetic theory results for the thermal conductivity of a polyatomic gas mixture. In this paper the simplification process is taken further in order to provide expressions for the thermal conductivity of a mixture of atomic and diatomic species that are both accurate and practical for the interpretation of experimental data. In particular, the thermal conductivity of the mixture can be cast in a form that is analogous to, and no more complicated than, the corresponding expression for entirely monatomic systems. The accuracy of the resulting expression is demonstrated with the aid of new calculations of the relevant kinetic cross sections for realistic potential models.

Theoretically based data assessment for the correlation of the thermal conductivity of dilute gases

This paper presents two schemes for a theoretically based data assessment of the thermal conductivity of dilute polyatomic gases. The first employs the simplified Thijsse expression, combined with accurate experimental data obtained from a transient hot-wire apparatus, as reference. The second makes use of theoretical results for the temperature dependence of the ratio Dint/D. Both methods lead to mutually consistent results for linear molecules and to useful criteria for discriminating between experimental data sets. The paper also demonstrates the influence of data burdened with systematic errors upon the final results of different correlation schemes.