E. Villar

Equations of state for hard spheres fluid in the metastable fluid region

A number of existing approximants are reviewed and tested for the equation of state of the hard spheres fluid in the metastable fluid region, namely, at densities higher than the normal freezing density: ρ*=0.943. This is a region which is particularly sensitive to the quality of a given equation of state; however, it is frequently ignored in the study of analytical equations of state. A new set of approximants is also discussed, including as particular cases several other currently used equations of state for the hard spheres fluid.

Behaviour of the internal pressure of liquids in accordance with variations in temperature, volume and cohesive energy density

Abstract A study is made of the variations to be found in the internal pressure of different types of liquid in accordance with variations in temperature and volume. These relationships are established through simple analytical equations. Variations in the cohesive energy density and the Hildebrand parameter in accordance with temperature variations are also calculated and it is shown that the internal pressure and the cohesive energy density are both analogous manifestations of the cohesion property of liquids and of the diminution of this property with falls in temperature.

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.

Temperature dependence of excluded volumes of some simple liquids from high density P-V-T data

Abstract The excluded volumes of the simple liquids Ar, Kr and Xe have been determined as a function of temperature from experimental high density P-V-T data. The results show a slight decrease as the temperature is raised in a similar way as the covolume does in the generalized Van der Waals theory.

A test of the modified Enskog theory for the transport properties of liquids

The modified Enskog theory (MET) has been applied to various fluids in the liquid range (between the triple point and the critical point), and the viscosity, thermal conductivity, and self-diffusion coefficients have been calculated. The temperature dependence of the covolume has been introduced explicitly, bypassing the use of virial coefficients. The agreement is generally acceptable and sometimes good. There is an evident regularity in the results when the reduced temperature is introduced as an independent variable.

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.