Equations for the GERG-2008 equation of state

We use the following equation to calculate the Helmholtz free energy (a(r,T,xi)) for the GERG-2008 equation of state (EOS):

where

a0 represents the properties of the ideal gas mixture

ar represents the properties of the residual mixture behavior

r is the density of the mixture

We use the following equations to calculate the ideal gas mixture term (a0):

where

rc,i is the critical density of component i

R is the molar gas constant (8.314472 J/mol/K)

R* is 8.314510 J/mol/K

Tc,i is the critical temperature of component i

n00i,k is a constant coefficient taken from Kunz and Wagner[1] for component i

q00i,k is a constant coefficient taken from Kunz and Wagner[1] for component i

We use the following equations to calculate the residual mixture behavior term (ar):

where

N is the total number of components in the mixture (21 components or less).

Fij is a fitted factor taken from Kunz and Wagner[1] for the binary component pair i and j.

KPol,i and KExp,i are constant values taken from Kunz and Wagner[1] for component i.

n0i,k is a constant coefficient taken from Kunz and Wagner[1] for component i.

d0i,k, t0i,k, and c0i,k are exponents taken from Kunz and Wagner[1] for component i.

KPol,ij and KExp,ij are constant values taken from Kunz and Wagner[1] for the binary component pair i and j.

nij,k is a constant coefficient taken from Kunz and Wagner[1] for the binary component pair i and j.

dij,k, tij,k, hij,k, eij,k, bij,k, and gij,k are exponents taken from Kunz and Wagner[1] for the binary component pair i and j.

rr is the reduced density of the mixture.

Tr is the reduced temperature of the mixture.

We use the following mixing rule to calculate the reduced density of the mixture (rr):

where

rc,i is the critical density of component i.

bv,ij and gv,ij are fitted binary parameters taken from Kunz and Wagner[1] for binary component pair i and j.

We use the following mixing rule to calculate the reduced temperature of the mixture (Tr):

where

Tc,i is the critical temperature of component i.

bv,ij and gv,ij are fitted binary parameters taken from Kunz and Wagner[1] for binary component pair i and j.

Currently, we use the GERG-2008 EOS only as a thermodynamic method override for liquid enthalpy, vapor enthalpy, and liquid density calculations. Therefore, we don’t use the GERG-2008 EOS for any vapor-liquid equilibrium calculations. See Effects of specifying thermodynamic method overrides for more information.

We use the following equation to calculate the enthalpy (H) in the liquid phase and vapor phase: