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Aspen Physical Property System - Physical Property Models

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Campbell-Thodos<br />

The Campbell-Thodos model uses the same equation and parameters as the<br />

Rackett model, above, except that Zm RA is allowed to vary with temperature:<br />

Zm RA<br />

=<br />

Campbell-Thodos also uses separately-adjustable versions of the critical<br />

parameters. Tmin and Tmax define the temperature range where the<br />

equation is applicable.<br />

Parameter<br />

Name/<br />

Element<br />

208 2 Thermodynamic <strong>Property</strong> <strong>Models</strong><br />

Symbol Default MDS Lower<br />

Limit<br />

Upper<br />

Limit<br />

Units<br />

RACKET/1 R*T ci/P ci R*Tci/Pci — — — MOLE-<br />

VOLUME<br />

RACKET/2 Z i *,RA<br />

RKTZRA x 0.1 1.0 —<br />

RACKET/3 d i 0 x 0 0.11 —<br />

RACKET/4 T min 0 x — — TEMPERATURE<br />

RACKET/5 T max 1000 x — — TEMPERATURE<br />

The Campbell-Thodos model is used when RACKET/3 is set to a value less<br />

than 0.11. The default value, 2/7, indicates that the standard Rackett<br />

equation should be used. When Campbell-Thodos is not used, RACKET/3<br />

should be kept at its default value of 2/7 for all components.<br />

References<br />

H.G. Rackett, J.Chem, Eng. Data., Vol. 15, (1970), p. 514.<br />

C.F. Spencer and R.P. Danner, J. Chem. Eng. Data, Vol. 17, (1972), p. 236.<br />

Modified Rackett Liquid Molar Volume<br />

The Modified Rackett equation improves the accuracy of liquid mixture molar<br />

volume calculation by introducing additional parameters to compute the pure<br />

component parameter RKTZRA and the binary parameter kij.<br />

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

Where:<br />

Tc<br />

kij<br />

=<br />

=<br />

=

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