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# Hauptinhalt

## PC-SAFT-PROP

### What it does

Generally

The subroutines will provide densities η and fugacity coefficients φ for one or two coexisting phases. The densities are obtained through iteration, applying a simple Newton algorithm. The following properties are involved:

 You give: Temperature T pressure p mole fractions of both phases xi' and xi'' starting values for the density in bith phases ηsta' and ηsta'' You get: densities η' and η'' fugacity coefficients φi' and φi''
Note: η is a dimensionless density, which is commonly called packing fraction. (See definition of variables used in PC-SAFT-PROP).

The file offered for download represents a compromise between computational effectiveness and transparency in programming. Each user may focus on different aspects and may personalize the subroutines and the structure accordingly.

Structure / Calling sequence of subroutines

The file PC-SAFT-PROP contains 6 subroutines. The calling sequence is illustrated in the scheme below. SUBROUTINE PC-SAFT-PROP is the entrance to all other subroutines. SUBROUTINE PHIEOS calculates the fugacity coefficients and along the way calls PERTPAR, DENSITR and F_EOS. The SUBROUTINE DENSITER will iterate the density and will repeatedly call P_EOS. What does each subroutine do?

 FUGACY This subroutine serves as an interface (the only interface) between a program that performs phase equilibrium calculations and the part of your program that contain all the PC-SAFT specific subroutines. It calls Subroutine PHIEOS for each phase. PHIEOS Calculates the fugacity coefficient. It calls F_EOS, PERTPAR and DENSITR DENSITR DENSITR iterates the density of one phase. If temperature and pressure are specified, the density is iterated to be consistent with those specifications. DENSITR requires a starting value for the appropriate density. If a vapor-liquid equilibrium is to be calculated, one starting density may be ηsta=10-10 for the vapor phase and ηsta=0.4 for the liquid phase, whereas starting values of ηsta=0.4 are a good approximation for both phases for the case of liquid-liquid equilibria. F_EOS Gives the residual Helmholtz free energy according to the Perturbed-Chain SAFT equation of state. P_EOS Calculates the pressure (in Pa) and the derivative of pressure to density (dp/dη) according to the Perturbed-Chain SAFT equation of state for given values of temperature and density. PERTPAR Provides constants and density independent expressions for the above described subroutines.
You can find instructions on the implementation of PC-SAFT-PROP here.

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