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Aspen Physical Property System - Physical Property Models

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HF, WILS-LR, and WILS-GLR. It is recommended for highly nonideal systems,<br />

especially alcohol-water systems. It can also be used in the advanced<br />

equation-of-state mixing rules, such as Wong-Sandler and MHV2. This model<br />

cannot be used for liquid-liquid equilibrium calculations.<br />

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

Where:<br />

ln Aij<br />

180 2 Thermodynamic <strong>Property</strong> <strong>Models</strong><br />

=<br />

The extended form of ln Aij provides more flexibility in fitting phase<br />

equilibrium and enthalpy data. aij, bij, cij, dij, and eij are unsymmetrical. That<br />

is, aij may not be equal to aji, etc.<br />

The binary parameters aij, bij, cij, dij, and eij must be determined from data<br />

regression or VLE and/or heat-of-mixing data. The <strong>Aspen</strong> <strong>Physical</strong> <strong>Property</strong><br />

<strong>System</strong> has a large number of built-in binary parameters for the Wilson<br />

model. The binary parameters have been regressed using VLE data from the<br />

Dortmund Databank. The binary parameters were regressed using the ideal<br />

gas, Redlich-Kwong, and Hayden-O'Connell equations of state. See <strong>Physical</strong><br />

<strong>Property</strong> Data, Chapter 1, for details.<br />

Parameter<br />

Name/Element<br />

Symbol Default MDS Lower Limit Upper<br />

Limit<br />

WILSON/1 a ij 0 x -50.0 50.0 —<br />

†<br />

Units<br />

WILSON/2 b ij 0 x -15000.0 15000.0 TEMPERATURE<br />

††<br />

WILSON/3 c ij 0 x -— — TEMPERATURE<br />

††<br />

WILSON/4 d ij 0 x — — TEMPERATURE<br />

††<br />

WILSON/5 T lower 0 K x — — TEMPERATURE<br />

WILSON/6 T upper 1000 K x — — TEMPERATURE<br />

WILSON/7 e ij 0 x — — TEMPERATURE<br />

††<br />

The WILS-2 property method uses data set 2 for WILSON. All other Wilson<br />

methods use data set 1.<br />

† In the original formulation of the Wilson model, aij = ln Vj/Vi, cij = dij = eij =<br />

0, and<br />

bij = -(�ij - �ii)/R, where Vj and Vi are pure component liquid molar volume at<br />

25�C.<br />

†† If any of biA, ciA, and eiA are non-zero, absolute temperature units are<br />

assumed for all coefficients. If biA, ciA, and eiA are all zero, the others are<br />

interpreted in input units. The temperature limits are always interpreted in<br />

input units.

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