Modeling of multiphase thermodynamic equilibria of $\rm NaCl$–$\rm H_2\rm O$ binary mixture in a wide range of pressures and temperatures

A method is proposed for the determination of the multiphase thermodynamic equilibria of a binary $\rm NaCl$–$\rm H_2\rm O$ mixture over a wide range of pressures and temperatures, including the critical thermodynamic conditions and the $\rm NaCl$ melting point. The method is based on calculation of the thermodynamic potential of the mixture which is entropy as a function of pressure, enthalpy, and $\rm NaCl$ concentration. The potential is calculated from two mutually consistent equations of state. The first equation of state of the van der Waals type describes the parameters of the vapor and liquid phases and the supercritical fluid. The second, simpler, equation describes the parameters of the solid phase of the salt. The chemical potentials of the equations are consistent for the calculation of single-phase, two-phase, and three-phase equilibria of the vapor–liquid–solid phase type. The phase diagrams of the mixture in the pressure–enthalpy–composition and pressure–temperature–composition variables are constructed.