Bug in calculation of thermal conductivity for mixture gases

[modelica-trac-importer]

Reported by bernath on 28 Jun 2013 10:06 UTC
Hello everybody,
the results of the calculation for thermal conductivity of mixture gases
("Modelica.Media.IdealGases.Common.MixtureGasNasa.thermalConductivity") is not correct.
I think the bug is, that the gas constant is not assigned in the function

lambdaX[i] :=SingleGasNasa.thermalConductivityEstimate(Cp=cp[i], eta=eta[i], method=method);

In function "Modelica.Media.IdealGases.Common.SingleGasNasa.thermalConductivityEstimate" the value "data.R" is always 0

lambda := if method == 1 then eta*(Cp - data.R + (9/4)*data.R) else eta*(Cp-data.R)*(1.32 + 1.77/((Cp/Modelica.Constants.R) - 1.0));

I've corrected the bug with an additional input "Rs" in "...MixtureGasNasa.thermalConductivity"

lambdaX[i] :=SingleGasNasa.thermalConductivityEstimate(Cp=cp[i], eta=eta[i],method=method,Rs=Modelica.Constants.R/fluidConstants![1].molarMass);

and in
"...SingleGasNasa.thermalConductivityEstimate"

lambda := if method == 1 then eta*(Cp - Rs + (9/4)*Rs) else (eta)*(1.32*Cp+0.45*Rs);

Maybe it is not the smartest solution, but now the calculation is correct.

Best regards
Michael Bernath
bernath@tum.de

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Migrated-From: https://trac.modelica.org/Modelica/ticket/1187

[modelica-trac-importer]

Comment by hubertus on 28 Jun 2013 12:54 UTC
If my memory does not fail me this bug was fixed in trunk, but I have no time to verify this now.

[modelica-trac-importer]

Comment by otter on 1 Jul 2013 12:11 UTC
I quickly checked by running on the trunk ModelicaTest.Media.TestOnly.DryAirNasa with DryAirNasa (a polynomial is used to determine thermal conductivity) and Modelica.Media.IdealGases.MixtureGases.CombustionAir (a mixture of N2 and O2; thermal conductivity is computed by SingleGasNasa.thermalConductivityEstimate. In both cases nearly the same thermal conductivity is computed.

To summarize, this bug was already fixed on trunk.