ConstDensityThermo standardConcentration is incorrect #458
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decaluwe
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Dec 5, 2017
Fixes Cantera#458. standardConcentration for species k is calculated as density()/molecularWeight(k). Note that any species with a molecularWeight of zero (i.e. a vacancy) will cause problems, and should be avoided for this phase. For this reason, sofc-text.xml also had to be changed and models the YSZ electrolyte as an `IdealSolidSolution`, rather than as `incompressible_solid`.
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Cantera version:
2.3.0
Operating System:
All
Expected Behavior:
constDensityThermo, as the name implies, holds the mass density (kg/m3) of the phase fixed. The standard concentration for species k should therefore be the molarDensity when X_k = 1, i.e.
Actual Behavior:
Instead, ConstDensityThermo:standardConcentration returns molarDensity(), meaning the standard concentration varies with the composition of the phase. This is incorrect, in and of itself, but also implies that the kinetics are handled incorrectly for this phase: for any thermodynamically reversible reaction where the number of product and reactant species in this phase are not equal (i.e. for certain interfacial reactions), k_f will be a function of X_k, which is clearly problematic.
The fix is relatively straightforward, and I'll submit a PR in short order, but just wanted to document and make sure I'm thinking about this correctly.
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