Thermodynamics of polyatomic fluid mixtures—I theory

Heat transfer, a review of current literature

Monte Carlo simulations on mixture systems composed of hydrogen molecules and helium atoms have been performed to develop an improved one‐fluid van der Waals model. This model is applicable to three‐parameter potentials having an exponential‐6 form. The proposed model has been shown to be as accurate as the conventional one‐fluid van der Waals model, but it can be used over an extended density and temperature range, where the conventional model is physically less appropriate.

Simple mixing rule for mixtures with exp-6 interactions

https://www.cheric.org/files/research/ip/g200104/g200104-201.pdf

A Helmholtz energy equation of state for calculating the thermodynamic properties of fluid mixtures

It is a hundred years since van der Waals related the pressure, volume and temperature of a fluid by the equation which bears his name. This article which is based on a lecture delivered at an Institute of Physics Conference at the University of Kent in April, describes the background and present value of his work.

Legacy of van der Waals

A new ideal K value is defined which does not depend on the Lewis and Randall ideal solution rule but is derived only from composition dependent pseudo criticals and the corresponding states principle. Properties of the liquid and vapor mixtures are evaluated from either experimentally measured properties of closely related pure substances or from generalized tables of thermodynamic properties. A derivation of an improved pseudocritical expression applicable to liquids which may be approximated by simple spherical molecules is presented. The derivation illustrates the assumptions involved and points the way for a possible extension of the technique to more complex molecules.

There are some advantages to this approach. It does not require the troublesome extrapolation of liquid properties into regions where no liquid can exist, a fact which is characteristic of K value calculations from the ideal solution rule. It is especially useful for systems in which an equation of state is not available for all of the components present. It avoids the difficulties in defining combination rules for complicated equations of state. Even for systems including very complex or moderately polar molecules it provides a base for subsequent empirical modification. This base follows the correct isotherm of In K vs. In P up to the actual critical of the system without the difficulties associated with defining a convergence pressure or evaluating the extremely large activity coefficient corrections to the ideal solution rule in the critical region. For mixtures of simple molecules the calculated ideal K value is within about 10% of the experimental value in both the low pressure and in the critical region. The entire calculation may be expressed completely analytically for use on a digital computer and may be coupled with an equilibrium flash calculation so that the ideal K values may be determined from a given overall composition, temperature, and pressure.

Bernard W. Gamson

Papers

Prediction of vapor‐liquid equilibria from the corresponding states principle