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, 4th ed., (New York: McGraw-Hill, 2001).

The following expressions define the terms leading to the equation for G^EX.

t₁₂ = exp{-u₁₂/(R×T)} and t₂₁ = exp{-u₂₁/(R×T)}
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}

G^EX/(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.)