J.R. Solana

Equations of state for D-dimensional hard sphere fluids

Abstract An equation of state, a kind of generalized Pade approximant, first proposed for the hard-sphere fluid in three dimensions is extended to the two-, four-, and five-dimensional cases in addition to the trivial one-dimensional case (hard rods). The corresponding equations of state show good to excellent agreement with existing simulation data.

Equations of State for Four-and Five-Dimensional Hard Hypersphere Fluids

Abstract Equations of state for the four- and five-dimensional hard hypersphere fluids have been obtained. Several procedures have been considered in each case: a) adapting the method of Carnahan and Starling to such dimensionalities; b) introducing Pade and Levin approximants suitable to the virial expansion and c) establishing a pole at a given density. In most cases, the results obtained agree satisfactorily with the available simulation data. The use of an additional fitting parameter furnishes nearly perfect agreement.

Behaviour of the equation of state of simple liquids at high pressures

Abstract The equation of state of the simple liquids Ar, Kr and Xe is analyzed at high pressures along a series of isotherms which cover the whole range of existence of the liquid phase. It is found that the experimental data behave similarly to the equation of state of a system of hard spheres at high densities. A parallel is established between this behaviour and that observed by various authors related with some transport properties.

Behaviour of the equation of state of liquid methane at high pressures

Abstract The equation of state of liquid methane is analyzed at high pressures along a series of isotherms which cover a substantial part of the range of existence of the liquid phase. It is found that experimental data are well reproduced by means of an equation of state which was initially proposed for the high density hardsphere system, provided that the effective excluded volume is properly determined for each isotherm. These effective excluded volumes decrease slightly as the temperature increases.

Behaviour of the equation of state of liquid nitrogen at high pressures

Abstract The equation of state of liquid nitrogen is analyzed at high pressures along a series of isotherms which cover a substantial part of the range of existence of the liquid phase. It is found that the experimental data obey an equation of state initially proposed for the high density hard-sphere system, provided that we properly account for the degree of coupling between the rotational and translational degrees of freedom and determine an adequate effective excluded volume for each isotherm. A parallel is established with the rough hard-sphere model for the self-diffusion constant of molecular liquids.

Temperature, pressure and volume dependence of the Grüneisen parameter of dense gaseous and liquid argon

Abstract The Gruneisen parameter is analyzed for dense gaseous and liquid argon. It is found that, similarly to solids, in the liquid region this parameter is nearly independent of temperature along isochores, whereas, contrary to its behaviour for solids, it increases with pressure and density along isotherms.

Behaviour of the equation of state of some liquid n-alkanes at high pressures

The equation of state of several liquid n-alkanes is analyzed along a series of isotherms in the liquid region. It is found that, for a substantial range of pressures for each isotherm, the experimental data are well reproduced by an equation of state, which was initially proposed for the high density hard-spheres system and later proved to be valid for several simple and molecular liquids, if we determined an effective excluded volume for each isotherm and provided that, in molecular liquids, we treat rotational degrees of freedom as equivalent translational ones.

Discussion of Some Thermoacoustical Relations for Simple Liquids

Abstract Our present work is an attempt to contrast the degree of validity for some proposed relations between temperature coefficients of the volume and the ultrasonic velocity making use of experimental results compiled by us and calculated data using the significant structures theory. There is a fair correlation between the experimental and theoretical values, except in the neighbourhood of the triple point. We conclude that the theory is useful for prediction in the absence of experimental data.

Relationship between excluded volume and effective molecular volume for some simple liquids

Abstract The excluded volumes of simple liquids Ar, Kr and Xe, determined by the authors as a function of temperature in a previous work, are compared with the effective volumes at regular close packing calculated in this work, for the same temperatures, by means of several procedures proposed in the literature. Good agreement is found with the different types of amorphous packing obtained experimentally or from computer simulation by several authors for the hard spheres system.

On the Divergency of the Equation of State of the Hard-Sphere Fluid at High Densities

Abstract The possible existence and situation of a singularity in the equation of state of the hard-sphere fluid at high densities is analysed from the existing simulation data, the known virial coefficients and Pade approximants. The convenience of introducing a prefixed pole in obtaining approximants for the equation of state of the hard-sphere fluid on the basis of the virial expansion is also discussed.