Application of the extended corresponding states method to the calculationof the ammonia-water mixture thermodynamic surface

The paper presents an application of the one-fluid extended corresponding s tates method to the calculation of the thermodynamic surface of the ammonia -water mixture. Each pure component of the mixture is considered as a refer ence fluid, and to lest the behavior of the model in wide ranges of tempera ture and pressure, the Haar-Gallagher and the Pruss-Wagner equations of sta te were chosen for pure ammonia and water, respectively. To avoid numerical problems during the calculation of the pure-component equivalent substance reducing ratios (or scaling factors), a method based on the mapping define d by the extended corresponding states algorithm and two-dimensional interp olation is proposed. The estimation of the binary interaction parameters wa s performed using the general case of the Least squares method, i.e., the c ase when all measurements (observations) and unknowns are subject to uncert ainty and are adjusted simultaneously with the constraint equations. The re sults show a strong temperature and composition dependence of both interact ion parameters for the liquid, as well as for the vapor phase. A formulatio n for the binary interaction parameters as continuous functions of these va riables was also derived and optimized using the structural optimization an d regression analysis. The final statistical quality of the approach presen ted in the paper was assessed using the available data on thermophysical pr operties of the mixture.