AREA METHOD FOR PREDICTION OF FLUID-PHASE EQUILIBRIA

A new method is developed to predict and calculate phase equilibria from equations of state for binary and ternary fluid mixtures to high pressures, including the critical and retrograde regions. The method minimizes the Gibbs energy by integrating, rather than differentiating, the Gibbs energy curve. The area method provides a sufficient condition for global Gibbs energy minimization, rather than only the necessary condition provided by the tangent-plane methods. The area method performs well along phase boundaries and has approached mixture critical points to within 10 mK from both the bubble and dew point curves. Cricondentherm temperatures have been calculated to within 10 nK and pressures within 0.1 mbar. The area method has been tested with several binary systems, including a three-phase system. An example further shows how the method may be extended to a ternary system. The results are in good agreement with examples from the literature, which used previous Gibbs minimization techniques.