Aspen Physical Property System - Physical Property Models

� Entropy:
� Heat capacity:
� refers to an arbitrary phase which can be solid, liquid, or ideal gas. For each
phase, multiple sets of parameters from 1 to n are present to cover multiple
temperature ranges. The value of the parameter n depends on the phase.
(See tables that follow.) When the temperature is outside all these
temperature ranges, linear extrapolation of properties versus T is performed
using the slope at the end of the nearest temperature bound.
The four properties Cp, H, S, and G are interrelated as a result of the
thermodynamic relationships:
There are analytical relationships between the expressions describing the
properties Cp, H, S, and G (equations 1 to 4). The parameters an,i to hn,i can
occur in more than one equation.
The Aspen Physical Property System has other models which can be used to
calculate temperature-dependent properties which the BARIN equations can
calculate. The Aspen Physical Property System uses the parameters in
THRSWT to determine which model is used. See Pure Component
Temperature-Dependent Properties for details.
If this parameter is 200 to 211 Then the BARIN equations are
used to calculate
THRSWT/3 Liquid vapor pressure
THRSWT/5 Solid heat capacity
THRSWT/6 Liquid heat capacity
THRSWT/7 Ideal gas heat capacity
The liquid vapor pressure is computed from Gibbs energy as follows:
ln p = (G L - G V )/RT + ln p ref
where p is the vapor pressure, and p ref is the reference pressure 101325 Pa.
Thus, parameters for both liquid and vapor are necessary to calculate vapor
pressure.
Solid Phase
The parameters in range n are valid for temperature: Tn,l s < T < Tn,h s
2 Thermodynamic Property Models 229
(4)
(3)