[thermo] fix plasma enthalpy_mole

[BangShiuh]

Fix issue #1306

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

[codecov]

Codecov Report

Merging #1323 (b940d27) into main (957dd24) will increase coverage by 0.02%.
The diff coverage is 98.76%.

@@            Coverage Diff             @@
##             main    #1323      +/-   ##
==========================================
+ Coverage   70.79%   70.82%   +0.02%     
==========================================
  Files         373      373              
  Lines       53873    53949      +76     
  Branches    17579    17587       +8     
==========================================
+ Hits        38141    38208      +67     
- Misses      13331    13339       +8     
- Partials     2401     2402       +1     

Impacted Files	Coverage Δ
interfaces/cython/cantera/thermo.pyx	92.07% <66.66%> (-0.11%)	⬇️
include/cantera/thermo/PlasmaPhase.h	81.39% <100.00%> (+9.96%)	⬆️
src/thermo/IdealGasPhase.cpp	92.99% <100.00%> (-0.14%)	⬇️
src/thermo/PlasmaPhase.cpp	77.91% <100.00%> (+7.52%)	⬆️
...terfaces/dotnet/Cantera/src/Interop/InteropUtil.cs	60.75% <0.00%> (-8.87%)	⬇️
src/base/stringUtils.cpp	79.03% <0.00%> (-0.81%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[ischoegl]

@BangShiuh … do you have any updates on this PR?

[BangShiuh]

@ischoegl There are some issues defining the thermodynamic properties of plasma. I am still working on it.

[BangShiuh]

@speth The consistency test is very helpful to get the thermodynamics correct. However, I still failed for case gk_eq_hk_minus_T_sk. Also in the case hk_eq_uk_plus_P_vk, I use RTe instead of p * vk[k] because I am not sure how to define a partial molar volume for electrons.

[speth]

For gk_eq_hk_minus_T_sk, I think you could mark that as an "expected failure" as the test doesn't know that it should use the electron temperature for the electron species in that summation. If you add a test in the PlasmaPhase specific tests that checks this identity with the right temperature being used for each species, I think that would be an appropriate alternative.

In the second case, is there a problem with using the same definition of the partial molar volume as used for the gas phase species (which is just the inverse of the mixture molar density, for all species)? I guess the question becomes whether the distinct electron temperature is being considered in the equation of state or not.

[BangShiuh]

@speth Any thought on this PR?

[speth]

Thanks for the updates to this, @BangShiuh. The main parts of the implementation all look reasonable to me. I just had a few questions / suggestions for your consideration.

[speth]

Why does this comparison have to be removed?

[BangShiuh]

Mixture thermal properties like enthalpy_mole() are not applicable for PlasmaPhase because it has gas and electron temperature.

[speth]

The initial point of this PR was to provide a working implementation of enthalpy_mole, though. I pushed an alternative that selectively disables the two methods called by compareThermo that are not implemented in PlasmaPhase (cp_mole and entropy_mole).

[speth]

This looks good to me. @ischoegl - I'd like to leave final approval of this to you, since I stuck a commit of my own in here and don't want to be just approving my own code, even if it is relatively minor.