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.)