Thermodynamic and transport properties of gases from sophisticated potential models

The statistical mechanical equations for the thermophysical properties of dilute gases are evaluated using sophisticated, but still practical potential models with no more than three adjustable parameters. Universal combination rules for these parameters are formulated. It is shown that some data of dilute gas thermophysical properties of monatomic and simple linear molecules yield potential parameters that can be used to predict all other thermophysical properties of the pure gases and their mixtures with excellent accuracy. For monatomic fluids, these potentials are shown to give excellent results of the thermodynamic functions also in the liquid and dense gaseous state.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Correlation and extrapolation of dilute-gas properties of simple linear molecules with the SSR-MPA potential model

A three-parameter angle-dependent pair potential referred to as the SSR-MPA is used to correlate and extrapolate the dilute-gas properties of the simple linear molecules nitrogen, oxygen, and ethane. The statistical mechanical equations are solved by direct numerical integrations. When the shape of the molecules and the anisotropic long-range forces are properly accounted for, all data are reproduced or predicted essentially within the experimental uncertainties.     

Dilute-gas mixture properties from pure-component data

The second virial coefficient, dilute-gas viscosity, and binary diffusion coefficients of some binary-gas mixtures are predicted from potentials which have been fitted to the properties of the pure components. It has been noted that the SSR-MPA potential for polyatomic and the MSK potential for monatomic molecules together with a suitable set of universal combination rules are adequate to make predictions essentially within the inaccuracy of the data.     

Equation of state for compressed liquids and their mixtures from the cohesive energy density

A procedure is presented, based on statistical-mechanical theory, for predicting the equation of state of compressed normal liquids and their mixtures from two scaling constants that are available from measurements at ordinary pressures and temperatures. The theoretical equation of state is that of Ihm, Song, and Mason, and the two constants are the enthalpy of vaporization and the liquid density at the triple point, which are related to the cohesive energy density of regular solution theory. The procedure is tested on a number of substances ranging in complexity from Ar and CO₂ to n-heptane and toluene. The results indicate that the liquid density at any pressure and temperature can be predicted within about 5%, over the range from T _tp to T _c and up to the freezing line. Possible methods of determining the scaling constants are discussed, as well as other possible choices for scaling constants.Paper dedicated to Professor Joseph Kestin.     

Forced modes of dilute binary gas mixtures

Anomalous forced sound dispersion in dilute binary gas mixtures is studied as a function of the mass ratio of the two components, using one- and two-temperature theories as well as different interparticle potentials. For a disparatemass mixture, such as He-Xe, the results are compared with previous work due to Johnson et al. It is suggested that even for nondisparate-mass mixtures, a one-temperature treatment is not appropriate.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

The dilute-gas properties of some systems containing CO2

The SSR-MPA potential model is used to correlate and extrapolate the dilutegas properties of some systems containing CO₂. With parameters determined from a consistent set of second virial and Joule-Thomson data, the third virial coefficient of CO₂ as well as the second virial coefficients of various mixtures containing CO₂ can be predicted very well. The Mason-Monchik approximation fails for a complicated molecule such as CO₂, although at least a viscosity prediction of technical accuracy is obtained. If parameters fitted to the CO₂ viscosity are used, excellent predictions can be made for the viscosity of gaseous mixtures containing CO₂.     

A numerical method for the thermodynamic properties of monatomic ionized gases

A numerical method for the direct computation of the particle densities, mass density, enthalpy and specific heat at constant pressure of a monatomic ionized gas in thermodynamic equilibrium is presented. This method permits calculation of the thermodynamic properties without iteration or numerical differentiation of any of the formulae.     

Composition dependence of the thermal conductivity of low-density polyatomic gas mixtures

We present a predictive scheme for the composition dependence of the thermal conductivity of mixtures containing polyatomic gases at zero density. This supplements earlier work which developed a method to interpolate for the composition dependence of dense gas mixtures, as well as an earlier procedure to calculate the thermal conductivity of mixtures of monatomic gases. In all cases, the algorithm makes use of accurately measured values of the thermal conductivity of pure gases and is validated with the aid of almost equal accurately measured values of selected binary mixtures. Such accurate data have been obtained mostly in transient hot-wire instruments. The formulae proposed for the calculations use the Monchick-Pereira-Mason kinetic-theory analysis as a starting point but contain a number of detailed improvements. The present algorithm is tested by comparison with measurements on 22 mixtures, which show absolute average deviations from the predictions ranging from 0.7 to 2.7%, with one unexplained case, that of CF₄-He mixtures, which show deviations reaching as much as 7%. We estimate that the algorithm predicts the zerodensity thermal conductivity of binary mixtures, containing at least one polyatomic component, with a probable error in the order of 2%.     

Thermophysical properties of molten salts: Hypersonic velocities of molten alkali nitrates and their mixtures

By means of Brillouin scattering spectroscopy, hypersonic velocities in NaNO₃-KNO₃ binary melts have been measured at temperatures from the liquidus temperatures of the melts to 200 K above them over the entire range of compositions. The light beam scattered by the melt is analyzed with a pressure-scanned Fabry-Perot spectrometer. The hypersonic velocities obtained are about the same as the ultrasonic velocities reported at compositions rich in NaNO₃, but are markedly larger than those at compositions rich in KNO₃, indicating the occurrence of structural relaxation. Thermodynamic values such as adiabatic and isothermal compressibilities, constant-volume heat capacity, and internal pressure calculated from the sound velocity obtained show that the melt can be treated as a typical ionic liquid, though it contains a certain amount of associated species.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, Tokyo, Japan.     

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.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The mixing effects for real gases and their mixtures

The definitions of the adiabatic and isothermal mixing effects in the mixing processes of real gases were presented in this paper. Eight substances with boiling-point temperatures from cryogenic temperature to the ambient temperature were selected from the interest of low temperature refrigeration to study their binary and multicomponent mixing effects. Detailed analyses were made on the parameters of the mixing process to know their influences on mixing effects. Those parameters include the temperatures, pressures, and mole fraction ratios of pure substances before mixing. The results show that the maximum temperature variation occurs at the saturation state of each component in the mixing process. Those components with higher boiling-point temperatures have higher isothermal mixing effects. The maximum temperature variation which is defined as the adiabatic mixing effect can even reach up to 50 K, and the isothermal mixing effect can reach about 20 kJ/mol. The possible applications of the mixing cooling effect in both open cycle and closed cycle refrigeration systems were also discussed.     

Ways of improving the accuracy of certification for gravimetric standard gas mixtures

A requirement is substantiated for improving the accuracy of certification for gravimetric standard gas mixtures (GSGM). Principles are developed for external quality control of GSGM for working standards of the zero order with application of statistical monitoring methods for quality according to a quantified characteristic. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 33–36, February, 2007.     

Calculation of the thermal conductivity of dense real gases and their mixtures

A procedure is proposed for calculating the thermal-conductivity coefficients of compressed gases and their mixtures; the real first density correction is introduced into the Enskog equation with allowance for the contribution of the internal degrees of freedom of the molecules.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 34, No. 5, pp. 849–853, May, 1978.     

Bounds on the effective properties of some multiphase matrix mixtures of coated-sphere geometry

Some matrix multiphase mixtures of Hashin's coated-sphere assemblage geometry with homogeneous spherical inclusions, coated by spherical shells made from an isotropic matrix-phase are considered. The inclusions are randomly assigned the properties of different inclusion phases with the frequencies according to their volume fractions. In the first case, the inclusion phases are isotropic. In the other case, the inclusions are anisotropic, their relative anisotropic orientations are random. The explicit upper and lower estimates for the effective conductivity and bulk modulus of such configurations are derived.     

A method of correlating the law of corresponding states in calculating the thermodynamic properties of real gases and their mixtures

A method of correlating the law of corresponding states is described, aimed at enhancing the accuracy of calculation of the thermodynamic properties of gases and mixtures of gases.     

Initial density dependence of experimental viscosities and of calculated diffusion coefficients of the binary vapor mixtures methanol-benzene and methanol-cyclohexane

The paper reports experimental results for the viscosity of the vapor mixtures methanol-benzene (five mole fractions with densities up to 1.5kg·m^–3 and 0.022 mol·L ^–1) and methanol-cyclohexane (four mole fractions with densities up to 1.9kg·m^–3 and 0.026 mol·L ^–1). In analogy to the pure components, the measurements on the mixtures were carried out with an oscillating-disk viscometer with small gaps, completely made of quartz, beginning as near as possible to room temperature and continuing to a maximum temperature of 630 K. A first evaluation by means of the Chapman-Enskog theory of dilute gases has shown differences in the resulting values of the interaction viscosity _ij ⁽⁰⁾ in the limit of zero density exceeding the experimental errors. Consistent results were obtained by taking into account the initial density dependence of the viscosity within the framework of the modified Enskog theory for gaseous mixtures. The values of _ij ⁽⁰⁾ were also used to estimate binary diffusion coefficients of the mixtures.     

Laboratory versus plant production: impact of material properties and performance for RAP and RAS mixtures

Agencies are moving towards performance-based design methodologies for asphalt pavements, and different methods to evaluate the asphalt performance in the laboratory have been developed. The laboratory performance can be evaluated at the mix design and/or production stages. A good understanding of differences in the behaviour of mixtures produced in the laboratory and plant is required to assess anticipated field performance at the mix design stage. The objectives of this paper are to compare the measured properties of plant-produced and laboratory-produced mixtures, to evaluate the effect of mixture variables on the differences observed, and to translate these to anticipated differences in fatigue performance through pavement evaluation using a linear viscoelastic layered analysis. In this study, 11 plant mixed, plant compacted, and their corresponding laboratory-mixed, laboratory-compacted mixtures are evaluated through binder and mixture testing. Mixture variables include aggregate gradation, binder grade and source, and recycled materials’ type and content. Performance grading on extracted and recovered binders, and complex modulus and SVECD fatigue testing on mixtures were conducted, and fatigue life was predicted using layered viscoelastic pavement design for critical distresses software. Most of the results show the laboratory mixtures are generally stiffer than the plant mixtures, but there is no constant shift for all mixtures. Larger differences are observed for the 19 mm and PG 58-28 mixtures and binder source appears to influence the differences as well. Different plants result in different effects on the properties of plant and lab-produced mixtures. This study provides a unique set of data that expands understanding of differences between laboratory and plant production of asphalt mixtures.     

Calculation of the compressibility factor of natural gases based on the calorific value and the specific gravity

The measurement of large volume flows of natural gas in transmission lines requires an accurate equation of state for pressures up to about 12 MPa and in the temperature range from 265 to 335 K. If a detailed analysis of the gas mixture is available, one of the possibilities is to use the virial equation of state. However, such a gas analysis is time-consuming and expensive and, therefore, not always practical. We have developed a new equation which is based on the virial equation but requires limited input data. In general, for any given natural gas, the gross calorific value, the specific gravity, and the mole fractions of nitrogen and carbon dioxide are known. It will be shown that a knowledge of three of these four quantities is sufficient for an accurate prediction of the compressibility factor of the natural gas.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.