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Difference in Molar Enthalpies between EoS and DFT #68

@RolfStierle

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@RolfStierle

Contributions.IdealGas uses different methods for EoS and DFT (see below).

Joback gives very small values for the IdealGas molar enthalpy (as fat as I tested all in the range ~1e-13 * JOULE).

import numpy as np

from feos.si import *
from feos.pcsaft import *

from feos.eos import EquationOfState, Contributions
from feos.eos import State as EosState
from feos.eos import PhaseEquilibrium as EosPhaseEquilibrium

from feos.dft import HelmholtzEnergyFunctional, PhaseEquilibrium
from feos.dft import State as DftState
from feos.dft import PhaseEquilibrium as DftPhaseEquilibrium

substances = ['nitrogen', 'methane']
params = PcSaftParameters.from_json(substances=substances, pure_path='pure_parameters.json', binary_path='binary_parameters.json', search_option=IdentifierOption.Name)

eos = EquationOfState.pcsaft(params)
dft = HelmholtzEnergyFunctional.pcsaft(params)

vle_eos = EosPhaseEquilibrium.bubble_point(eos, temperature_or_pressure=110*KELVIN, liquid_molefracs=np.array([0.1, 0.9]))
vle_dft = DftPhaseEquilibrium.bubble_point(dft, temperature_or_pressure=110*KELVIN, liquid_molefracs=np.array([0.1, 0.9]))

print(vle_eos.liquid.helmholtz_energy_contributions()) # Gives QSPR as IdealGas contribution
print(vle_dft.liquid.helmholtz_energy_contributions()) # Gives Joback as IdealGas contribution

print(vle_eos.liquid.molar_enthalpy(contributions=Contributions.ResidualNvt) - vle_dft.liquid.molar_enthalpy(contributions=Contributions.ResidualNvt)) #Gives very good agreement in the ResidualNvt contribution

print(vle_eos.liquid.molar_enthalpy(contributions=Contributions.IdealGas) - vle_dft.liquid.molar_enthalpy(contributions=Contributions.IdealGas)) # Gives large discrepancy in IdealGas contribution

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