There are multiple open source equations of state libraries, like:

• Clapeyron julia
• FeOs rust with Python bindings
• teqp C++ with Python bindings
• thermo python
• thermopack Fortran with Python bindings
• CoolProp C++ with Python bindings

Here we are presenting yet another (still in development) one, that tackles the same problem just, in another way. Mostly exploiting the readability and extensibility of Modern Fortran for scientists to have an easy way to implement new thermodynamic models without dealing with lower-level languages but still getting decent performance. And also this framework provides the possibility of using analytically obtained derivatives so both options are easily available.

This is an experimental work in progress and we recommend the before mentioned libraries if you are intending to use some of this in real work. Big part of the code comes from a refactoring process of older codes so not all parts are easily readable, yet.

We focus mainly on that the addition of a new thermodynamic model as easily as possible. Also providing our models too!

For now, we only include residual Helmholtz model (like Cubic or Saft Equations of State). But we'll be adding other models like $G^E$ (UNIFAC for example).

A little taste of yaeos

A lot of users get the bad picture of Fortran being old and archaic since most of the codes they've seen are written in ancient F77.

use yaeos, only: PengRobinson76, pressure, ArModel

integer, parameter :: n=2   ! Number of components
real(8) :: V, T, P, dPdN(n) ! variables to calculate
class(ArModel), allocatable :: model ! Model

real(pr) :: z(n), tc(n), pc(n), w(n), kij(n, n), lij(n, n)

z = [0.3, 0.7]
tc = [190., 310.]
pc = [14., 30.]
w = [0.001, 0.03]
kij = reshape([0., 0.1, 0.1, 0.], [n,n])
lij = kij / 2 

model =  PengRobinson76(tc, pc, w, kij, lij)

V = 1
T = 150

call pressure(model, z, V, T, P)
print *, P

! Obtain derivatives adding them as optional arguments! 
call pressure(model, z, V, T, P, dPdN=dPdN)
print *, dPdN

How to install/run it

yaeos is intended to use as a fpm

You can either:

• Generate a new project that uses yaeos as a dependency

fpm new my_project

In the fpm.toml file add:

[dependencies]
yaeos = {git="https://github.com/ipqa-research/yaeos"}

• Clone this repository and just modify the executables in the app directory

git clone https://github.com/ipqa-research/yaeos
cd yaeos
fpm run

Including new models with Automatic Differentiation.

We are using the hyperdual module developed by Philipp Rehner and Gernot Bauer

The automatic differentiation API isn't fully optimized yet so performance is much slower than it should be.

type, extends(ArModelAdiff) :: YourNewModel
   type(Substances) :: composition
   real(8), allocatable :: parameters(:) ! A vector of parameters
contains
   procedure :: Ar => arfun
   procedure :: get_v0 => v0
end type

subroutine arfun(self, n, v, t, Ar)
   class(YourNewModel), intent(in) :: self
   type(hyperdual), intent(in) :: n(:) ! Number of moles
   type(hyperdual), intent(in) :: v ! Volume [L]
   type(hyperdual), intent(in) :: t ! Temperature [K]
   type(hyperdual), intent(out) :: ar_value ! Residual Helmholtz Energy

   ! A very complicated residual helmholtz function of a mixture
   Ar = sum(n) * v * t / self%parameters(1)
end subroutine

function v0(self, n, p, t)
   class(YourNewModel), intent(in) :: self
   real(pr), intent(in) :: n(:) ! Number of moles
   real(pr), intent(in) :: p ! Pressure [bar]
   real(pr), intent(in) :: t ! Temperature [K]
   real(pr) :: v0

   v0 = self%parameters(3)
end function

A complete implementation of the PR76 Equation of State can me found in example/adiff/adiff_pr76.f90.

All the thermodynamic properties can be found in yaeos_thermoprops and called like:

use yaeos_thermoprops, only: fugacity_vt
use my_new_model, only: YourNewModel
...
type(YourNewModel) :: eos
eos%parameters = [1, 2, 3]
call fugacity_vt(eos, n, v, t, lnfug=lnfug, dlnphidn=dlnphidn)

Documentation

The latest API documentation for the main branch can be found here. This was generated from the source code using FORD. We're working in extending it more.