Mathematical model for exergy in the system NaCl-H2O

In this work mathematical models for the exergy and relative enthalpy of the water solution of sodium-chloride and the pure crystalline sodium-chloride where derived. The environment was defined with the temperature 20 °C, pressure 101,325 kPa and with liquid water and crystalline sodium-chloride, both having at the defined environmental conditions the value of exergy equal zero. The obtained mathematical model is valid in the temperature interval from 0 to 170°C and for the all compositions of solution, until to saturation. The derived mathematical model for the exergy is based on the Pitzer's ion interaction equation which satisfactory represents the dependence of the osmotic coefficient and the mean ionic activity coefficient on the composition of solution. The calculated values of exergy using the mathematical model were compared with the appropriate diagram for the exergy constructed using the table values of activity coefficients, osmotic coefficients and partial molar enthalpies.