Equations of state for fluids: The Dieterici approach revisited

In 1873, van der Waals proposed a simple equation of state that qualitative ly described the phase behavior of fluids. Since then, the principles behin d the van der Waals equation have been used and refined countless times in the quest for an accurate equation of state. Despite the enormous amount of work reported, the goal of a simple and accurate equation of state for eve n relatively simple systems, such as monatomic or polyatomic gases, has pro ved elusive. Therefore, the analysis of phase equilibria with equations of state is more often than not an exercise in data fitting rather than genuin e prediction. In this work, we revisit the early work of Dieterici. When co upled with modern developments in equations of state, this little used appr oach has the potential of generating useful equations of state. To illustra te the usefulness of the Dieterici formula, we use it to derive a simple eq uation of state based on the Carnahan-Starling hard-sphere term and van der Waals interactions. This simple approach yields more accurate predictions of the phase co-existence of fluids than the traditional additive approach used to develop equations of state. (C) 2001 American Institute of Physics.