Density, volume and compressibility factor
The sections below discuss the various density models available in TEA.
Volume is always calculated as one over density.
Compressibility factor the ratio of pressure times volume and gas constant times temperature: PV/RT. Compressibility factor is only available when using an equation of state.
Liquid mixture density
All mixture density derivatives are determined by perturbation, except for the Amagat method.
Mixture liquid densities are calculated with one of the following models
Equation of State
If an equation of state is selected for the liquid phase, density can be calculated using the equation of state.
Amagat's law (Ideal)
Amagat's law calculated mixture density by ideally mixing the volumes for the available compounds:
See the section below for the pure compound liquid densities ρiL.
This method requires compound critical temperatures, pressures, mole weights and Rackett parameters (for which critical compressibilities are used if unknown):
If the reduced temperature, Tr, is greater than unity the formula above is evaluated for Tr = 1.
Mixture critical temperature, volume, and compressibility are calculated with the "normal" mixing rules. If the mixture reduced temperature, Tr = T / Tc,m, is greater than unity the density is evaluated using Tr = 1.
Mixture density is calculated by the COSTALD method of Hankinson and Thomson (AIChE J, 25, 653, 1979) and Thomson et al. (AIChE J, 28, 671, 1982):
If the reduced temperature is larger than unity, the following is evaluated using unity for the reduced temperature:
|b= 1.43907||f= 0.386914|
The density equals the inverse of the liquid molar volume.
This method should be used for reduced temperatures from 0.25 up to the critical point.
Pure compound liquid density
Pure compound liquid densities are required by some of the above mixture liquid density routines, and are only valid in this context. If an external density calculation routine is used, pure compound liquid densities are evaluated fore each compound by setting the mole fraction of that compound to unity and the remaining mole fractions to zero, and evaluate mixture density.
Pure compound liquid densities are computed with one of the following methods. Depending on the choice of mixture liquid density (see above), the choices for pure compound mixture density may be limited in order to be consistent.
All derivatives are determined by perturbation, except for the EOS method.
The temperature correlation for pure compound liquid density is a polynomial of which the parameters are available through TEA's PCD data files.
The Rackett method for pure compound liquid density:
As for liquid mixture density, but with pure compound parameters.
When selecting the Per Compound routine, the above methods can be selected on a per-compound basis in the compounds tab.
Equation of State
As for liquid mixture density.
The only available vapor density methods use the selected vapor equation of state.
The only available mixture solid density calculation routine is Amagat's law (see above for liquid). The only available compound solid density calculation routine is temperature correlation.
Overall density is not available.
Overall volume can be calculated through summation over the available phases.