Intermolecular repulsions and the equation of state for fluids

Abstract

Abstract This investigation demonstrates the advantages of an improved expression for intermolecular repulsions in equations of state. A highly accurate equation of state for the rigid‐sphere fluid is used as the model of repulsion behavior in real fluids. A method for general usage of this new rigid‐sphere equation in real fluid models is presented via reformulation of van der Waal's equation using the accurate new rigid‐sphere equation to describe repulsion effects. To test this reformulation, properties of methane, ethane, propane, n‐butane, isobutane, hydrogen sulfide, nitrogen, ethylene, acetylene, methyl chloride, cyclohexane, pentane and octane have been calculated. The advantage of using the accurate rigid‐sphere equation was demonstrated by the general improvement in calculated properties relative to the original van der Waals and Redlich‐Kwong equations. Calculations of enthalpy departures for mixtures of nitrogen and methane, propane and methane, pentane and cyclohexane, and pentane and octane also indicated the desirability of using the accurate rigid‐sphere equation to describe repulsion effects in mixtures.