Available values of the surface tension of 81 common fluids were fitted by using the same model presently used in the REFPROP program V9.0 by NIST. A set of data was built for every fluid by including mainly those values given in the DIPPR and DETHERM databases. For some fluids, other available sources of data were added in order to obtain adequate sets. For every fluid, we checked the accuracy of the REFPROP program and we made a new fit in order to improve the performance of the correlation. We found good general agreement between the REFPROP predictions and the data for 44 fluids, and therefore only very slight improvements are made for them. For the other 37 fluids, the REFPROP correlation can be more clearly improved. In particular, our new correlation is significantly more accurate for ammonia, deuterium, ethanol, and neon, because the version of REFPROP used gives values in clear disagreement with other data sources.

When thermodynamic properties of a pure substance are transformed to reduced form by using both critical- and triple-point values, the corresponding experimental data along the whole liquid-vapor coexistence curve can be correlated with a very simple analytical expression that interpolates between the behavior near the triple and the critical points. The leading terms of this expression contain only two parameters: the critical exponent and the slope at the triple point. For a given thermodynamic property, the critical exponent has a universal character but the slope at the triple point can vary significantly from one substance to another. However, for certain thermodynamic properties including the difference of coexisting densities, the enthalpy of vaporization, and the surface tension of the saturated liquid, one finds that the slope at the triple point also has a nearly universal value for a wide class of fluids. These thermodynamic properties thus show a corresponding apparently universal behavior along the whole coexistence curve.

Twenty two di †erent analytical expressions for the compressibility factor of the hard sphere system have been collected and reviewed in order to perform two applications : Firstly, the accuracy of these expressions in reproducing six available computer simulation data sets for the hard sphere system, some of which are very recent, is tested. It is shown that there is not a direct relation between the simplicity or complexity of their analytical form and their accuracy. Secondly, the expressions, together with the VerletÈWeis formula for the temperature dependence of the molecular diameter, have been used to reproduce our molecular dynamics results for the pressure of the Lennard-Jones reference system proposed in the WeeksÈChandlerÈAndersen theory. We conclude that the approximation of using hard sphere equations of state together with the VerletÈWeis formula is very accurate at temperatures and densities near the Lennard-Jones critical point. At densities close to the triple point or to the liquid curve in the liquidÈvapour equilibrium, the coincidence is adequate (deviations around 3%) only if the appropriate hard sphere equation of state is used.

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ABSTRACT:The asymptotic expansion method is extended by using currently available accurate values for the first ten virial coefficients for hard sphere fluids. It is then used to yield an equation of state for hard sphere fluids, which accurately represents the currently accepted values for the first sixteen virial coefficients and compressibility factor data in both the stable and the metastable regions of the phase diagram.2