Showing papers by "Peter T. Cummings published in 1993"

Shear viscosity of model mixtures by nonequilibrium molecular dynamics. I. Argon–krypton mixtures

Abstract: We present nonequilibrium molecular dynamics simulations of argon–krypton liquid mixtures at constant temperature and pressure (T=135 K and P=40 bar) as the base case for a consistent study of the role of intermolecular potentials on the transport properties of molecular liquids and their mixtures. Using Lennard‐Jones models for the two species, very good agreement with experiment is obtained for the thermodynamic and transport properties of the two pure fluids. Simulations at constant temperature and density using the Barker–Fisher–Watts potentials for pure fluids yields predictions for thermodynamic properties and viscosity in excellent agreement with experiment.

Non-Equilibrium Molecular Dynamics Calculation of the Shear Viscosity of Carbon Dioxide/Ethane Mixtures

Abstract: Non-equilibrium molecular dynamics simulations of the shear viscosity of mixtures of carbon dioxide and ethane at a fixed total density (20 mole-dm3) and at five compositions ranging from pure carbon dioxide to pure ethane are reported. In this study, two-site Lennard-Jones potential models are used for all the inter-molecular interactions. The cross parameters of ethane/carbon dioxide potential have been fitted to the azeotrope of the mixture. Results from the simulations are in good agreement with experimental data. In particular, a plateau region in the experimental data as a function of composition is reproduced by the simulations but is not predicted by extended corresponding states correlations.

Relationship between McQuarrie and Helfand equations for the determination of shear viscosity from equilibrium molecular dynamics

Abstract: A proof of the validity of the Chialvo-Debenedetti conjecture [Phys. Rev. A 43, 4289 (1991)], the crucial element to achieve an equivalence between the McQuarrie [Statistical Mechanics (Harper Row, New York, 1976)] and Helfand [Phys. Rev. 119, 1 (1960)] shear-viscosity equations, is presented here. Some theoretical consequences of that validity are also discussed, such as the unification of most shear-viscosity expressions into one given by Andrews for first-order transport coefficients [J. Chem. Phys. 47, 3161 (1967)]. The system-size dependence of the McQuarrie shear-viscosity values is analyzed and an extrapolation method is proposed and tested to determine the asymptotic values.

Relationship between McQuarrie and Helfand equations for the determination of shear viscosity from equilibrium molecular dynamics

Abstract: A proof of the validity of the Chialvo-Debenedetti conjecture [Phys. Rev. A 43, 4289 (1991)], the crucial element to achieve an equivalence between the McQuarrie [Statistical Mechanics (Harper & Row, New York, 1976)] and Helfand [Phys. Rev. 119, 1 (1960)] shear-viscosity equations, is presented here. Some theoretical consequences of that validity are also discussed, such as the unification of most shear-viscosity expressions into one given by Andrews for first-order transport coefficients [J. Chem. Phys. 47, 3161 (1967)]. The system-size dependence of the McQuarrie shear-viscosity values is analysed and an extrapolation method is proposed and tested to determine the asymptotic values

Structure of Mixed Solvent Electrolyte Solutions via Gibbs Ensemble Monte Carlo Simulation

Abstract: Previously reported Gibbs ensemble Monte Carlo simulations of vapor-liquid equilibrium in methanol-water and methanol-water-NaCl mixtures are extended to permit study of the microscopic structure of the liquid phases of these systems. The salt effect in a prototypical mixed solvent electrolyte solution (water-methanol-NaCl) is microscopically interpreted in terms of the structural changes undergone by the solvation shells of the ions in the liquid phase of water-methanol-NaCl systems in vapor-liquid equilibrium at constant pressure.

Unified expression for the calculation of thermal conductivity in the canonical ensemble

Abstract: A proof of the theoretical equivalence between the E. Helfand, 1960, Phys. Rev., 119, 1 and the D. McQuarrie, 1976, Statistical Mechanics (Harper & Row), Chap. 21 equations for the calculation of thermal conductivity via the Einsteintype relations is presented here. Some theoretical implications of that equivalence are also discussed, such as the unification of the thermal conductivity expressions into one similar to that given for linear transport coefficients by F. C. Andrews, 1967, J. Chem. Phys., 47, 3161.