IdealSolidSolnPhase::getPartialMolarEnthalpies - needs pressure dependence?

[decaluwe]

Problem description
The getPartialMolarEnthalpies routine in IdealSolidSolnPhase would appear to be missing the required pressure dependence implemented elsewhere in the model.

All other enthalpy (and, by association, chemical potential) calculations involve some form of (P - Pref)*molarVolume (where molarVolume is of either the phase or the individual species).

IdealSolidSolnPhase::getPartialMolarEnthalpies does not:

void IdealSolidSolnPhase::getPartialMolarEnthalpies(doublereal* hbar) const
{
    const vector_fp& _h = enthalpy_RT_ref();
    scale(_h.begin(), _h.end(), hbar, RT());
}

I think this ought to be replaced with:

void IdealSolidSolnPhase::getPartialMolarEnthalpies(doublereal* hbar) const
{
    const vector_fp& _h = enthalpy_RT_ref();
    scale(_h.begin(), _h.end(), hbar, RT());
    double delta_p = (m_Pcurrent - m_Pref);
    for (size_t k = 0; k < m_kk; k++) {
        hbar[k] += delta_p * m_speciesMolarVolume[k];
    }
}

System information

• Cantera version: 2.6.0a2

Wanted to check if I was missing something, before fixing it.

[speth]

Seems correct to me. If you follow through the more convoluted logic for the similar IdealSolnGasVPSS class, the (P - Pref)*molarVolume term does get added to the standard state enthalpy, which then gets carried through to the partial molar enthalpies.

[decaluwe]

Sorry if this is dense, but: "seems correct to me" meaning "the current implementation seems correct," or "your critique seems correct?" 🙄

Since IdealSolidSolnPhase does not add the pressure term to the standard state values, I'll assume you mean the latter 😉. Just to make sure, I did a little check:

import cantera as ct
import numpy as np

gas = ct.Solution('IdealSolidSolnPhaseExample.yaml',"solidSolutionExample")

# At standard pressure: h_mole = sum(X_k*h_k)
h_mole = gas.enthalpy_mole
h_k = gas.partial_molar_enthalpies

h_check = np.dot(h_k,gas.X)
print(h_mole, h_check)
5895465.481744414 5895465.481744414

# At non-standard pressure, h_mole shows the correct pressure dependence, but the partial molar enthalpies do not:
gas.TP = None, 3*ct.one_atm
h_mole = gas.enthalpy_mole
h_k = gas.partial_molar_enthalpies
h_check = np.dot(h_k,gas.X)
print(h_mole, h_check)
6199440.481744414 5895465.481744414

When I originally created this issue, I thought we were considering folding IdealSolnGasVPSS into this class. But since the opposite is true, I will hold off on doing anything about this, for now.

[speth]

Yes, I meant your interpretation seems correct and IdealSolidSolnPhase does not.

[decaluwe]

lol, thanks for the confirmation :)