Fix pressure dependence in IdealSolidSolnPhase::getPartialMolarEnthalpies

[decaluwe]

Changes proposed in this pull request

• Adds proper pressure dependence to IdealSolidSolnPhase::getPartialMolarEnthalpies

If applicable, fill in the issue number this pull request is fixing

Closes #1080

If applicable, provide an example illustrating new features this pull request is introducing
Previously, the partial molar enthalpies had no pressure dependence for this class. As a check, the sum of partial molar enthalpy times mole fraction should equal the average phase molar enthalpy. Prior to this change:

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_check = np.dot(gas.partial_molar_enthalpies, gas.X)
print(h_mole - h_check)
0

# 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_check = np.dot(gas.partial_molar_enthalpies, gas.X)
print(h_mole, h_check)
303975

With the implemented correction:

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_check = np.dot(gas.partial_molar_enthalpies, gas.X)
print(h_mole - h_check)
0

# 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_check = np.dot(gas.partial_molar_enthalpies, gas.X)
print(h_mole, h_check)
0

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[decaluwe]

One question: I moved the "multiply by RT" step into the for loop. Would it be faster, computationally, to keep this outside the loop, using scale?

[codecov]

Codecov Report

Merging #1087 (e0f84fa) into main (78f893f) will increase coverage by 0.01%.
The diff coverage is 87.85%.

❗ Current head e0f84fa differs from pull request most recent head f09de99. Consider uploading reports for the commit f09de99 to get more accurate results

@@            Coverage Diff             @@
##             main    #1087      +/-   ##
==========================================
+ Coverage   73.45%   73.46%   +0.01%     
==========================================
  Files         362      364       +2     
  Lines       47554    47626      +72     
==========================================
+ Hits        34929    34987      +58     
- Misses      12625    12639      +14     

Impacted Files	Coverage Δ
include/cantera/base/global.h	93.33% <ø> (ø)
include/cantera/kinetics/GasKinetics.h	100.00% <ø> (ø)
include/cantera/kinetics/Kinetics.h	55.88% <0.00%> (ø)
include/cantera/kinetics/MultiRate.h	82.60% <ø> (ø)
include/cantera/kinetics/Reaction.h	100.00% <ø> (ø)
src/clib/ct.cpp	8.29% <0.00%> (-0.06%)	⬇️
src/thermo/IdealSolidSolnPhase.cpp	68.65% <83.33%> (+0.23%)	⬆️
src/kinetics/GasKinetics.cpp	92.61% <85.71%> (-0.43%)	⬇️
src/kinetics/Reaction.cpp	89.20% <85.71%> (-1.24%)	⬇️
src/kinetics/ReactionRateFactory.cpp	93.33% <93.33%> (ø)
... and 18 more

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[decaluwe]

FYI, I'm going to add a test to check that h_mole = sum(h_k * X_k), as in the commit message.

[decaluwe]

Okay, once the tests finish running, this should be ready for review.

[speth]

Looks good to me.

As to the question about calling scale versus multiplying by RT() inside the loop, I think the latter (as you've opted for) is better, as it involves only one loop -- the scale function would have to loop internally anyway.