Liquid Activity Methods
These methods use liquid activity coefficients to model the liquid phase behavior. The Poynting correction for pressure may be applied to the liquid phase and the standard state liquid fugacities and vapor phase fugacity coefficients may be computed with an equation of state. For super-critical gases and for trace solutes, Henry's constants may be used to define the standard state fugacity. The activity methods work best for mixtures of components which do not differ greatly in volatility and have strongly non-ideal liquid interactions. See Liquid Activity Coefficients for further information on this approach to phase equilibria.
The following systems are provided in this category. The name for each system is defined from the Equilibrium K-value method.
Non-random Two-liquid Equation (NRTL)
K-values: NRTL method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Universal Quasi-chemical (UNIQUAC)
K-values: UNIQUAC method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
K-values: VANLAAR method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
K-values: WILSON method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
K-values: MARGULES method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Regular Solution Theory (REGULAR)
K-values: REGULAR method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
K-values: FLORY method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Universal Functional Activity Coefficient (UNIFAC)
K-values: UNIFAC method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Lyngby-modified UNIFAC (UNIFAC TDep-1)
K-values: UNIFAC TDep-1 method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Dortmund-modified UNIFAC (UNIFAC TDep-2)
K-values: UNIFAC TDep-2 method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Modified UNIFAC method (UNIFAC TDep-3)
K-values: UNIFAC TDep-3 method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Free volume modification to UNIFAC (Free Volume)
K-values: Free Volume method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
K-values: Ideal method
Enthalpies, entropies, densities, vapor fugacities: Ideal method
Additional Information
Many options are provided when calculating K-values with liquid activity methods. These options may be reached via the Thermodynamics System - Modification Window and include the following: fill options for missing liquid phase activity coefficients, Poynting correction options, Henry's law options, selection of LLE key components and databank search order for liquid activity coefficient data. The method used for the standard state liquid fugacity coefficients and vapor phase fugacity coefficients may also be selected and modified in this window.
Descriptions of the individual thermodynamic methods may be accessed from the Thermodynamic System - Modification Window by selecting the current property method and pushing the Help button. Further description may be obtained by selecting the property method under Related Topics in the help screen which is displayed.
Detailed information on the liquid activity coefficient methods, including complete descriptions of the equation forms may be obtained in PRO/II Reference Manual under the topic Liquid Activity Methods.
Related Topics