Van Der Waals Partition Function Research Articles

The generalized van der Waals partition function. II. Application to the square-well fluid

A formulation of the generalized van der Waals partition function derived earlier is used here, together with insights obtained from computer simulation, to develop two new equations of state for the square-well fluid. One of these equations is remarkably simple in form, and leads to compressibility factor, vapor pressure and orthobaric density predictions which are as good as, or better than, those obtained with the much more complicated equations of state which have been proposed in the past for the square-well fluid. Further, using this equation, with square-well parameters obtained from second virial coefficient data, and only one adjustable parameter, remarkably good predictions are obtained for the P-V-T and saturation properties of argon and methane.

Thermodynamics of benzene + alkane and cyclohexane + alkane systems. An estimation of the free volume

A thermodynamic model for multicomponent mixtures is derived introducing the Carnahan and Starling expression for the free volume in the van der Waals partition function. The derivation of the model is equivalent to the one for the Prigogine-Flory-Patterson (PFP) model, and our results are compared with those of the PFP model. Expressions for the equation of state, excess properties, thermal expansion and thermal pressure coefficients are given. The values of the characteristic parameters for some molecules are calculated, and the results of predicted excess properties are compared with those already known for the PFP model. The discussion of binary mixtures is centred on the families of systems formed by benzene or cyclohexane and an alkane.

Gas solubility calculations. II. Application of a new group-contribution equation of state

A new equation of state has been developed for polar as well as nonpolar components. It is based on the generalized van der Waals partition function and uses local-composition mixing rules. The group-contribution version of this equation of state (the GC-EOS) is described and tables containing parameters for 14 solvent groups and 9 gases (H 2, N 2, CO, O 2, CH 4, C 2H 4, CO 2, C 2H 6 and H 2S) are presented. The GC-EOS predicts vapor-liquid equilibria well for all kinds of systems involving the groups considered. The method requires only information concerning readily accessible pure-component properties. Calculations for multicomponent systems show that the method suggested provides very good predictions of multicomponent high-pressure vapor-liquid equilibria and fairly good predictions of Henry's constants in mixed solvents.

Generalized van der waals partition function for fluids. Modification to yield better second virial coefficients

When parameters in the generalized van der Waals partition function are evaluated from high-density data, predicted second virial coefficients are too positive. An empirical modification is suggested; this modification gives marked improvement in the second virial coefficient without significantly changing the fit for data in the high-density region. Illustrations are given for argon and for water. Extension to mixtures is stragihtforward.