Activity Coefficient Model: UNIQUAC
The model is described in: Bruce E. Poling, John M. Prausnitz, John P. O'Connell, The Properties of Gases and Liquids, 5th ed., (New York: McGraw-Hill, 2001).
The following expressions define the terms leading to the equation for GEX.
t12 = exp{-u12/(R
×T)} ; and t21 = exp{-u21/(R
×T)}; for the symmetric form, u12 = u21
t1 = (x1
×q1)/{x1
×q1 + (1 - x1)×q2} and t2 = {(1 - x1)×q2}/{x1
×q1 + (1 - x1)×q2}
f1 = (x1
×r1)/{x1
×r1 + (1 - x1)×r2} and f2 = {(1 - x1)×r2}/{x1
×r1 + (1 - x1)×r2}
GEX/(R ×T) = -q1 ×x1 ×ln(t1 + t2 ×t21) - q2 ×x2 ×ln(t2 + t1 ×t12) + x1 ×ln(f1/x1) + x2 ×ln(f2/x2) + 5{q1 ×x1 ×ln(t1/f1) + q2 ×x2 ×ln(t2/f2)}
Details of the model implementation in TDE, including ThermoML-Equation representation are available. (See the ThermoML web site for details of this IUPAC communication standard.)