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Aspen Physical Property System - Physical Property Models

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Rackett/Campbell-Thodos Mixture Liquid<br />

Volume<br />

The Rackett equation calculates liquid molar volume for all activity coefficient<br />

based and petroleum tuned equation of state based property methods. In the<br />

last category of property methods, the equation is used in conjunction with<br />

the API model. The API model is used for pseudocomponents, while the<br />

Rackett model is used for real components. (See API Liquid Volume .)<br />

Campbell-Thodos is a variation on the Rackett model which allows the<br />

compressibility term Zi *,RA to vary with temperature.<br />

Rackett<br />

The equation for the Rackett model is:<br />

Where:<br />

Tc<br />

Zm RA<br />

Vcm<br />

=<br />

=<br />

=<br />

=<br />

Tr = T / Tc<br />

Note: Reduced temperature Tr is always calculated using absolute<br />

temperature units.<br />

Note: Above Tr=0.99 an extrapolation method is used to smooth the<br />

transition to constant molar volume equal to the critical volume.<br />

Parameter<br />

Name/<br />

Element<br />

2 Thermodynamic <strong>Property</strong> <strong>Models</strong> 207<br />

Symbol Default MDS Lower<br />

Limit<br />

Upper<br />

Limit<br />

Units<br />

TC T ci — — 5.0 2000.0 TEMPERATURE<br />

PC p ci — — 10 5<br />

10 8<br />

PRESSURE<br />

VCRKT V ci VC x 0.001 3.5 MOLE-<br />

VOLUME<br />

RKTZRA Z i *,RA<br />

ZC x 0.1 1.0 —<br />

RKTKIJ k ij x -5.0 5.0 —

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