Dense Fluid Phase Research Articles

Molecular dynamics simulation of CH 4 in the dense fluid phase

A molecular dynamics study of methane in the dense fluid phase is reported. Systems studied consist of 108, 256 and 500 molecules, interacting with a site-site Lennard-Jones potential. Thermodynamic properties, the mean-squared force, the mean-squared torque and the site-site radial distribution function g CC ( r) are calculated. The compressibility and the phase transition from the liquid phase to the translational ordered phase are in good agreement with high-pressure experimental values.

Temperature and volume dependence of the thermal conductivity of solid neon

The thermal conductivity $\ensuremath{\kappa}$ of solid natural neon has been measured by the linear-flow method for specimens isobarically frozen from the dense-fluid phase within a high-strength steel cell. By crossing the fusion curve at several different pressures to as high as 7 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ bars, crystalline samples with molar volumes between 11.16 and 13.35 ${\mathrm{cm}}^{3}$/mole were grown, and for each the isochoric variation of $\ensuremath{\kappa}$ vs $T$ was determined at a set of temperatures in the experimentally accessible range between 5 and 40 K. The large magnitude of $\ensuremath{\kappa}$ and reproducibility of the results demonstrate that the present method of preparation and manipulation of solid neon consistently yields good-quality specimens. An analysis utilizing the zero-degree limit of the Debye temperature ${\ensuremath{\Theta}}_{0}$ to account for all volume dependence indicates that the array of data, when expressed in terms of the resistive mean free path, may be rendered into a single function of the inverse reduced temperature $\frac{{\ensuremath{\Theta}}_{0}}{T}$. The exponential variation of this common curve over more than 2 orders of magnitude is characteristic of three-phonon umklapp scattering and thereby gives support to Peierls's model of heat transport in dielectric crystals. More recent first-principles theoretical calculations are in qualitative agreement with experiment but yield conductivities somewhat below the observed values.

Modified cell theory: Equation of state for hard spheres

A modified cell theory - introducing a distribution of different cell sizes - is applied to hard spheres. Using a relation developed by Hoover a successful uniform equation of state is given for both the solid and the dense fluid phase.

Pulsed NMR study of submonolayer and multilayer 3He films adsorbed on Grafoil

The nuclear spin relaxation times T 1 and T 2 of submonolayer and multilayer 3He films adsorbed on Grafoil have been measured at temperatures between 1.2 and 4.2 K by a pulsed NMR technique. The T 1 data for high-coverage films (solid and dense fluid phases) and the substrate registered phase are interpreted in terms of thermally activated vacancies. In solids the quantum exchange inherent in 3He is shown to be important at low temperatures. The data for multilayer films are discussed in the light of the particle exchange between layers and the relaxation time of each layer. The dynamical behavior of adatoms in the solid, fluid, and substrate registered phases as well as the nature of phase transitions between them are discussed on the basis of information obtained from the analysis of T 1 and T 2 data. The present results as a whole seem to support the phase diagram determined by specific heat measurements. In addition, the nuclear susceptibility in submonolayer films has been measured by the same technique. The effect of Fermi degeneracy was not seen in the temperature range between 1.2 and 4.2 K.

Studies in molecular dynamics. XIV. Mass and size dependence of the binary diffusion coefficient

The velocity autocorrelation function and the binary diffusion coefficient of a single hard sphere test particle whose mass and size is less than that of the solvent are computed in the dense fluid phase. Large deviations from the Enskog theory of uncorrelated motion are found as the diffusion coefficient vanishes for the lighter and larger test particle at higher densities. Comparison with experimental values leads to the conclusion that the correlated motions observed in hard spheres correspond well to those observed in real systems.

Studies in Molecular Dynamics. VII. Hard-Sphere Distribution Functions and an Augmented van der Waals Theory

Hard-sphere radial distribution functions are evaluated in the dense fluid phase and compared to the predictions from various integral equations. Perturbation theory is then used to add various attractive potentials to the hard core in order to demonstrate the near constancy of the van der Waals energy density parameter a. The augmented van der Waals theory which replaces the parameter b by the hard-sphere equation of state and “a” by its theoretical value is then used to predict the dependence of the critical point on the shape of the intermolecular potential. The critical volume and temperature are found to be sensitively dependent on the range and depth of the intermolecular forces.

Superconducting Magnet Materials

Superconducting Magnet Materials

Viscosity of Hydrocarbon Gases Under Pressure

Abstract The viscosity of hydrocarbon mixtures, whether in the gas or liquid phase, is a function of pressure, temperature, and phase composition. This paper presents methods for the prediction of the viscosity of the gas or less dense fluid phase over the practical range of pressure, temperature, and phase compositions encountered in surface and subsurface petroleum production operations. The correlation necessary to predict the effect of pressure on viscosities is presented in Part I. Serious discrepancies in high pressure gas viscosity data in the literature are discussed. The application of the correlation to predict absolute viscosities is discussed in Part II. Auxiliary correlations are presented to enable calculations of viscosities from a knowledge of the pressure, temperature, and gravity of the gas phase. Introduction A knowledge of the viscosity of hydrocarbon fluids is needed to study the dynamical or flow behavior of these mixtures through pipes, porous media, or more generally wherever transport of momentum occurs in fluid motion. Since flow is predominantly in the laminar region in petroleum reservoirs, the influence of fluid viscosity on this flow is especially important. As early as 1894, Onnes and Onnes and de Haas noted that the viscosities of homologs under corresponding states could be correlated. The theorem of corresponding states has been further developed and applied to the viscosity of pure, nonpolar gases under pressure by Comings, Mayland, and Egly. Serious discrepancies in the viscosity of pure hydrocarbon gases at high pressures have been called to our attention by Comings, Mayland, and Egly. They made a careful analysis of the following methods commonly used to measure gas viscosities:Oscillating disc viscometer.Rolling ball viscometer.Capillary tube viscometer