.ThermalSeparation.Media.Correlations.FugacityCoefficient

Information

Vapour Phase

The fugacitiy coefficient can be calculated using different equations of state. This package contains some of these equations of state.

Virial equation of state

phi_vap is given by

• phi_vap_i = exp [ 2*(sum(yj*Bij) - B) * P/ (R*T)].

Bij are the virial coefficients for pure components(if i=j) and the cross-coefficients(if i!=j) , they can be either taken out of adequate literature, such as (Lit. [3]), or calculated with the correlations of Tsonopoulos (1974) (Lit. [1], 4.13, 5.10).

If the cross-coefficients are calculated, there are binary interaction coefficients kij in the mixing rule for the temperature. These binary constants are more or less between 1 and -1, just for giving an approximate range. The mixing rules are shown in (Lit.[1], 5.10; Lit.[4]). For the existing media models these constants are given and can be accessed just like other constants for instance the critical data. Additional data is given in (Lit. [4]).

For the Tsonopoulos correlation two specific substance constants are needed. They are a function of the critical data and the dipole moment, which is also given in the media package. For further calculations beyond the existing media models, a vector (eq_Tsonopoulos) has to be implemented, which refer on the necessary equations. The equations for the Tsonopoulos constants are shown in (Lit[1], 4.15).

Soave-Redlich-Kwong(SRK)

The Soave-Redlich-Kwong equation of state depends on two interaction parameters. The parameters are computed with the critical data and one of them has a temperature dependence. Furthermore for mixtures there are special relations. There is one further binary interaction parameter kij, which occur in the mixing rule for the cross coefficient aij. Some of these binary parameters are listed in (Lit. [4]). For the existing media models these parameters are accessable like the critical data.

The used mixing rules are the Van-der-Waals mixing rules, as it is recommanded in the literature.

Peng-Robinson(PR)

The Peng-Robinson equation of state differs just a little from the SRK. The application of the PR EoS is similar to the SRK.

References:

[1] Poling, Prausnitz, O'Connell : The Properties of Gases & Liquids 5th Edition [4.13, 5.10]

[2] Gmehling, Kolbe: Thermodynamik

[3] Dymond, Smith : The Virial Coefficients of Pure Gases and Mixtures

[4] Fluid Phase Equilibria 260 (2007) 354-358

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