THE AREA METHOD FOR PURE FLUIDS AND AN ANALYSIS OF THE 2-PHASE REGION

The Area method, developed recently for solving multicomponent phase e quilibrium problems, has been extended to pure fluids. The method is b ased on maximizing a single objective function in the Helmholtz-volume surface along any given isotherm, which reduces the number of indepen dent variables to only two: the saturated liquid and vapour volumes. T wo techniques are employed to find the maximum of the objective functi on, the integral and iterative. The integral always finds the thermody namically stable solution without any prior assumptions about the valu es of the molar volumes. This factor distinguishes the integral from t he iterative technique and also from methods based on the Maxwell equa l-area principle. The method has been applied to a group of high accur acy non-cubic equations of state and some of the thermodynamic inconsi stencies which occur inside the two-phase region are explored. A new i nequality constraint which eliminates these inconsistencies during the development of new equations of state is proposed, and initial result s with fitting a preliminary Helmholtz equation of state for benzene a re encouraging. (C) 1997 Elsevier Science B.V.