Modified Free Volume Theory of Self-Diffusion and Molecular Theory of Shear Viscosity of Liquid Carbon Dioxide (original) (raw)
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Non-equilibrium molecular dynamics calculation of the transport properties of carbon dioxide
Fluid Phase Equilibria, 1989
We compute the thermal conductivity and diffusion coefficient of supercritical carbon dioxide along the 313 K isotherm using non-equilibrium molecular dynamics. Comparisons are made with experiment at four densities corresponding to pressures of 30, 70, 200 and 500 bar. Two intermolecular potential models for carbon dioxide are compared. molecular dynamics (NEMD). This paper continues this study of the transport properties of supercritical fluids and focuses on the thermal conductivity and the self-diffusion coefficient of carbon dioxide along the 313 K supercritical isotherm. These papers are part of our continuing research program aimed at studying the transport properties of supercritical fluids using NEMD. The NEMD algorithms for computing thermal conductivity and self-diffusion coefficient are similar to the one used for the calculation of shear viscosity. All three algorithms involve
Living Journal of Computational Molecular Science, 2018
The ability to predict transport properties (e.g., diffusivity, viscosity, and conductivity) is one of the primary benefits of molecular simulation. Although most studies focus on the accuracy of the simulation output compared to experimental data, such a comparison primarily tests the adequacy of the force field (i.e. the model). By contrast, the reliability of different simulation methodologies for predicting transport properties is the focus of this manuscript. Unfortunately, obtaining reproducible estimates of transport properties from molecular simulation is not as straightforward as static properties. Therefore, this manuscript discusses the best practices that should be followed to ensure that the simulation output is reliable, i.e. is a valid representation of the force field implemented. We also discuss procedures to use so that the results are reproducible (i.e. can be obtained by other researchers following the same methods and procedures).
Heat and Mass Transfer, 2009
It is the purpose of this paper to extract unlike intermolecular potential energies of five carbon dioxidebased binary gas mixtures including CO 2-He, CO 2-Ne, CO 2-Ar, CO 2-Kr, and CO 2-Xe from viscosity data and compare the calculated potentials with other models potential energy reported in literature. Then, dilute transport properties consisting of viscosity, diffusion coefficient, thermal diffusion factor, and thermal conductivity of aforementioned mixtures are calculated from the calculated potential energies and compared with literature data. Rather accurate correlations for the viscosity coefficient of afore-cited mixtures embracing the temperature range 200 K \ T \ 3273.15 K is reproduced from the present unlike intermolecular potentials energy. Our estimated accuracies for the viscosity are to within ±2%. In addition, the calculated potential energies are used to present smooth correlations for other transport properties. The accuracies of the binary diffusion coefficients are of the order of ±3%. Finally, the unlike interaction energy and the calculated low density viscosity have been employed to calculate high density viscosities using Vesovic-Wakeham method. List of symbols A* Ratio of collision integrals a D Constant a a Constant a g Constant a k Constant B* Ratio of collision integrals b Impact parameter (m) b D Constant b a Constant b g Constant b k Constant C* Ratio of collision integrals c D Constant c a Constant c g Constant D ij Binary diffusion coefficient (m 2 /s) d a Constant d g Constant d k Constant E* Ratio of collision integrals e a Constant F* Ratio of collision integrals f D Higher order correction factor for the diffusion f a Constant f g Higher order correction factor for the viscosity G Inversion function h Plank's constant (Js) k Boltzman constant (J/K) k T
A Study of Molecular Transport in Liquid Mixtures Based on the Concept of Ultimate Volume
Industrial & Engineering Chemistry Fundamentals, 1976
A method for the characterization of transport properties of multicomponent liquid systems is developed by combining the concept of ultimate volume of pure liquids with the known behavior of the self-diffusion coefficient and extending the results to liquid mixtures. Comparison of the predictions of the resulting model with available data for several binary, ternary, and quaternary liquid systems yields excellent agreement. It is demonstrated that this approach, which does not involve any hypothesis concerning the existence of activated states, is capable of yielding accurate predictions of diffusion coefficients of liquid mixtures. These predictions require only readily accessible properties of the constituents of the mixtures.
The Journal of Physical Chemistry B, 2005
In this paper, we apply the Matteoli-Mansoori empirical formula for the pair correlation function of simple fluids obeying the Lennard-Jones potential to calculate reduced self-diffusion coefficients on the basis of the modified free volume theory. The self-diffusion coefficient thus computed as functions of temperature and density is compared with the molecular dynamics simulation data and the self-diffusion coefficient obtained by the modified free volume theory implemented with the Monte Carlo simulation method for the pair correlation function. We show that the Matteoli-Mansoori empirical formula yields sufficiently accurate self-diffusion coefficients in the supercritical regime, provided that the minimum free volume activating diffusion is estimated with the classical turning point of binary collision at the mean relative kinetic energy 3k B T/2, where k B is the Boltzmann constant and T is the temperature. In the subcritical regime, the empirical formula yields qualitatively correct, but lower values for the self-diffusion coefficients compared with computer simulation values and those from the modified free volume theory implemented with the Monte Carlo simulations for the pair correlation function. However, with a slightly modified critical free volume, the results can be made quite acceptable.
Self-Diffusion in Gases and Liquids
Industrial & Engineering Chemistry Research, 1997
A systematic study of the self-diffusion coefficient in hard-sphere fluids, Lennard-Jones fluids, and real compounds over the entire range of gaseous and liquid states is presented. First an equation is proposed for the self-diffusion coefficient in a hard-sphere fluid based on the molecular dynamics simulations of Alder et al. (J. Chem. Phys. 1970, 53, 3813) and Erpenbeck and Wood (Phys. Rev. A 1991, 43, 4254). That expression, extended to the Lennard-Jones fluids through the effective hard-sphere diameter method, represents accurately the self-diffusion coefficients obtained in the literature by molecular dynamics simulations, as well as those determined experimentally for argon, methane, and carbon dioxide. A rough Lennard-Jones expression, which contains besides the diameter σ LJ and energy LJ the translational-rotational factor, A D (which could be correlated with the acentric factor), is adopted to describe the self-diffusion in nonspherical fluids. The energy parameter is estimated using a correlation obtained from viscosity data, and the molecular diameter is obtained from the diffusion data themselves. The equation represents the self-diffusion coefficients with an average absolute deviation of 7.33%, for 26 compounds (1822 data points) over wide ranges of temperature and pressure.
On predicting self-diffusion coefficients from viscosity in gases and liquids
Chemical Engineering Science, 2007
The relations between self-diffusion and viscosity for compressed liquids and gases have been reviewed, and a new equation for correlating viscosities over wide ranges of temperature and pressure is proposed. This formula is inspired by the Lennard-Jones Chain model of Yu and Gao for self-diffusion, and represents the viscosities of 15 compounds (1046 data points) with an average absolute deviation of 6.95%. Moreover, as the presented equation and the Yu-Gao model require the same fitting parameters, the ability to calculate self-diffusion coefficients from the viscosity parameter is studied. Some of the classic reviewed relations, such as the Stokes-Einstein formula, are also contrasted with the available experimental data of both transport properties.
Transport coefficients of fluid mixtures
International Journal of Thermophysics, 1986
On the basis of the successful description of the equilibrium properties of simple fluids and fluid mixtures using perturbation theory, the consequences of including density-and temperature-dependent diameters in the formulas for the transport coefficients of dense hard-sphere fluid mixtures are investigated. The advantages and limitations of this approach for the correlation of the experimental data of real mixtures, together with numerical estimates for particular mixtures, are discussed. On the other hand, recent mean field kinetic theories which include the effect of the attractive tail in the intermolecular potential are employed to derive transport coefficients for mixtures. Numerical results are presented and comparison with other theories is also made.