Simulation of the properties of a binary carbon dioxide-water mixture under sub- and supercritical conditions

A method for determining the multiphase thermodynamic equilibriums of a binary mixture expressed in pressure-enthalpy-mixture composition variables is suggested. The use of such variables, in contrast to the classical thermodynamic pressure-temperature-composition variables, makes it possible to determine not only the two-phase, but also three-phase states of a mixture. The method can be used to describe real properties of mixtures in a wide range of pressure and temperature values containing critical points; it can be helpful in modeling of the mixture flows in a porous medium. The suggested problem of calculating the multiphase equilibrium can be visually interpreted in terms of geometry by constructing a convex envelope for the thermodynamic potential of the mixture. This method is used to study the phase diagram of the carbon dioxide-water mixture.