Wong–Sandler Mixing Rule

The Wong–Sandler mixing rule is a thermodynamic mixing rule used for vapor–liquid equilibrium and liquid-liquid equilibrium calculations.
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Summary

The first boundary condition is

:$b - \frac a = \sum_i \sum_j x_i x_j \left(b_ - \frac \right)$

which constrains the sum of ''a'' and ''b''. The second equation is

:$\underline A^_(T, P\to\infty, \underline x) = \underline A^_(T, P\to\infty, \underline x)$

with the notable limit as $P\to \infty$ (and $\underline_i\to b,$ $\underline_\to b$) of

:$\underline A^_ = C^* \left(\frac a b - \sum x_i \frac \right).$

The mixing rules become

:$\frac = Q \frac,\quad b = \frac$

:$Q = \sum_i \sum_j x_i x_j \left( b_ - \frac \right)$

:$D = \sum_i x_i \frac + \frac$

The cross term still must be specified by a combining rule, either

:$b_ - \frac = \sqrt (1 - k_)$

or

:$b_ - \frac = \frac(b_ + b_) - \frac(1 - k_).$

See also

:Vapor–liquid equilibrium
:Equation of state

References

Engineering thermodynamics
Thermodynamics
Equilibrium chemistry

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