Aspen Physical Property System - Physical Property Models

�k is the activity coefficient of a group at mixture composition, and �k i is the
activity coefficient of group k in a mixture of groups corresponding to pure i.
The parameters �k and �k i are defined by:
With:
And:
The parameter Xk is the group mole fraction of group k in the liquid:
Parameter
Name/Element
UFGRP (k,� k, m, � m, ...)
2 Thermodynamic Property Models 173
Symbol Default MDS Lower
Limit
Upper
Limit
— — — — —
GMUFQ Q k — — — — —
GMUFR R k — — — — —
Units
GMUFB b kn — — — — TEMPERATURE
The parameter UFGRP stores the UNIFAC functional group number and
number of occurrences of each group. UFGRP is stored in the Aspen Physical
Property System pure component databank for most components. For
nondatabank components, enter UFGRP on the Properties Molecular Structure
Functional Group sheet. See Physical Property Data, Chapter 3, for a list of
the UNIFAC functional groups.
UNIFAC-PSRK
The PSRK property method uses GMUFPSRK, the UNIFAC-PSRK model, which
is a variation on the standard UNIFAC model. UNIFAC-PSRK has special
groups defined for the light gases CO2, H2, NH3, N2, O2, CO, H2S, and argon,
and the group binary interaction parameters are temperature-dependent,