UNIFAC (NIST-Modified) Activity Coefficient Model: DETAILS

The model is similar to the NIST-KT-UNIFAC model. Details of the parameterization for NIST-KT-UNIFAC are given here: NIST-KT UNIFAC Parameter Details

Distinctions from the NIST-KT UNIFAC model follow.

Parameters A, B, and C for each pair of main groups for the particular binary mixture are available as part of the TDE output.

Temperature dependence of interaction parameters is given by:

The combinatorial contribution is represented by:


Indexes i and j (above) belong to the components of the mixture. The molecular volume and surface area fi and qi are calculated from subgroup contributions (specific for NIST-modified UNIFAC) Rk and Qk, where nik is the number of occurrences of the k-th subgroup in molecule i.