# Temperature-dependent emissivity for DOM boundary condition

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 September 28, 2009, 16:03 Temperature-dependent emissivity for DOM boundary condition #1 New Member   Join Date: Sep 2009 Posts: 4 Rep Power: 10 Hi, I am learning how to use buoyantSimpleRadiationFoam and looking at the tutorial tutorials/heatTransfer/buoyantSimpleRadiationFoam/hotRadiationRoomFvDOM. In this tutorial a constant emissivity is used for DOM: Code: ```dimensions [1 0 -3 0 0 0 0]; internalField uniform 0; boundaryField { ".*" { type greyDiffusiveRadiation; T T; emissivity 0.5; value uniform 0; } }``` I wonder how to modify it for temperature-dependent emissivity (i.e., polynomial functions of temperature). Thanks in advance!

 September 29, 2009, 19:04 #2 New Member   Jean Lachaud Join Date: Mar 2009 Location: Moffett Field, Ca Posts: 6 Rep Power: 10 Hi, 1) a quick and 'not recommended' option would to modify the boundary condition and recompile it in the following file src/thermophysicalModels/radiation/lnInclude/greyDiffusiveRadiationMixedFvPatchScalarField.C you will find refValue() = emissivity_*4.0*radiation::sigmaSB.value()*pow4(Tp ) /Foam::mathematicalConstant:i; you can replace it by (e.g.) emissivity_*(Tp/1000)*4.0*radiation::sigmaSB.value()*pow4(Tp) /Foam::mathematicalConstant:i; where Tp is the wall temperature and 1000 a linear factor you will need to recompile the boundary condition by executing "wmake libso" in the directory 'src/thermophysicalModels/radiation' 2) recommended method: read "Implement boundary condition" at http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2007/ It is explained how to copy the boundary condition (including .H file) in your own 'run' directory, modify it and recompile it. I hope this helps... Jean

 September 30, 2009, 18:36 #3 New Member   Join Date: Sep 2009 Posts: 4 Rep Power: 10 Thanks for your help, Jean. I will follow your second suggestion.

 September 30, 2009, 18:48 #4 New Member   Join Date: Sep 2009 Posts: 4 Rep Power: 10 Now I have another question about how to use temperature-dependent absorption coefficient. I am studying the case tutorials/heatTransfer/buoyantSimpleRadiationFoam/hotRadiationRoom. To use greyMeanAbsorptionEmision model, the radiationProperties dictionary was modified as Code: ```radiation on; radiationModel P1; noRadiation { } P1Coeffs { } // Number of flow iterations per radiation iteration solverFreq 1; absorptionEmissionModel greyMeanAbsorptionEmission; greyMeanAbsorptionEmissionCoeffs { lookUpTableFileName "speciesTable"; EhrrCoeff 0.0; } scatterModel constantScatter; constantScatterCoeffs { sigma sigma [ 0 -1 0 0 0 0 0 ] 0; C C [ 0 0 0 0 0 0 0 ] 0; }``` The speciesTable dictionary was created as well: Code: ```air { Tcommon 300.; invTemp true; Tlow 300.; Thigh 2500.; loTcoeffs ( 0 0 0 0 0 0 ); hiTcoeffs ( 18.741 -121.31e3 273.5e6 -194.05e9 56.31e12 -5.8169e15 ); }``` When I tried to run it, I got the following message: Code: ```keyword fields is undefined in dictionary "/home/navier/foam/buoyantSimpleRadiationFoam/hotRadiationRoom/constant/speciesTable" file: /home/navier/foam/buoyantSimpleRadiationFoam/hotRadiationRoom/constant/speciesTable from line 20 to line 42. From function dictionary::lookupEntry(const word&, bool, bool) const in file db/dictionary/dictionary.C at line 388. FOAM exiting``` What's wrong/missing in my dictionaries? I know probably it's a simple problem but I am new in OF.

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