Empirical equations for the thermodynamic properties of aqueous sodium chloride

Equations for the thermodynamic properties of aqueous sodium chloride near its vapour pressure are presented. The equations are functions of temperature and concentration, and may be used to estimate aqueous sodium chloride’s solubility, density, vapour pressure, specific enthalpy and entropy. They are valid for temperatures from 0 to 300°C, and concentrations extending to saturation with suitable accuracy. The thermodynamic equations are represented graphically and compared with published experimental data. These equations should prove to be a useful tool for modeling desalination equipment, particularly distillation processes.

Equations were presented that predict the solubility, vapour pressure, density, enthalpy and entropy of an aqueous solution of sodium chloride. The equations are valid near the solution’s vapour pressure for temperatures from 0–300°C and may be used for any concentration with increasing uncertainty above 0.26 sodium chloride mass fraction. The solubility, vapour pressure, density and heat capacity equations exhibited adequate agreement with experimental data. The data used to develop the enthalpy equation had an underlying error of +/–20% and thus both the enthalpy and entropy have a similar uncertainty. More accurate enthalpy equations could be developed if more plentiful data taken with standardized procedures were available for analysis. The equations and curves presented herein should prove to be a useful tool for modeling desalination equipment, particularly distillation processes.