Aspen Physical Property System - Physical Property Models

Note: Reduced temperature Tr is always calculated using absolute
temperature units.
Parameter Symbol Default MDS Lower Upper Units
Name/Element
Limit Limit
TC T ci — — 5.0 2000.0 TEMPERATURE
PC p ci — — 10 5
Soave Modification
74 2 Thermodynamic Property Models
10 8
(4)
PRESSURE
The parameter �i is a temperature function introduced by Soave in the
Redlich-Kwong equation-of-state to improve the correlation of the pure
component vapor pressure:
Equation 3 still holds. The parameter mi can be correlated with the acentric
factor:
Equations 1, 2, 3, 5 and 6 are the standard Redlich-Kwong-Soave
formulation. The Soave alpha function is adequate for hydrocarbons and other
nonpolar compounds, but is not sufficiently accurate for polar compounds.
Parameter
Name/Element
Symbol Default MDS Lower
Limit
(5)
(6)
Upper
Limit
Units
TCRKS T ci TC X 5.0 2000.0 TEMPERATURE
PCRKS p ci PC X 10 5
OMGRKS � i OMEGA X -0.5 2.0 —
Boston-Mathias Extrapolation
10 8
PRESSURE
For light gases at high reduced temperatures (> 5), equation 5 gives
unrealistic results. The boundary conditions are that attraction between
molecules should vanish for extremely high temperatures, and reduces
asymptotically to zero. Boston and Mathias derived an alternative function for
temperatures higher than critical:
With
di
ci
=
=
Where:
(7)