# Possible error in the BC of the wideBandDiffusive radiation model

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 April 27, 2017, 06:13 Possible error in the BC of the wideBandDiffusive radiation model #1 New Member   Adrien Join Date: Apr 2013 Posts: 2 Rep Power: 0 Hi Foamers, I would like to have feedback on the following problem I found using the fvDOM radiation model with the wideBandAbsorptionDiffusive model. The BCs for solving the RTE are calculated at the wall through the wideBandDiffusiveRadiation BC. This BC uses the radiation emitted by the wall. This is calculated using the emissivity of the wall (temissivity in the code below) and black body radiation at the temperature of the wall (Eb). Code: ``` refValue()[faceI] = ( Ir[faceI]*(1.0 - temissivity[faceI]) + temissivity[faceI]*Eb[faceI] )/pi; // Emmited heat flux from this ray direction Qem[faceI] = refValue()[faceI]*nAve[faceI]``` In my understanding of the band model, Eb should be the fraction of the radiation emitted by the blackbody in the wavelength range of the considered band. However it seems that the BC is instead using the full blackbody emissive power. I related this to the fact that the blackBodyEmission.C performs a loop on the whole internal temperature but not on its the boundaries. A simple test for that was to add a counter Code: ``` else { int j=0; forAll(T, i) { j+=1; scalar T1 = fLambdaT(band[1]*T[i]); scalar T2 = fLambdaT(band[0]*T[i]); dimensionedScalar fLambdaDelta ( "fLambdaDelta", dimless, T1 - T2 ); Eb()[i] = Eb()[i]*fLambdaDelta.value(); Info << "j=" << j << endl; } return Eb; }``` It appeared that this doesn't loop in the temperature BC, thus Eb remains equal to the initialized value that is sigma T. It seems to me that this is problematic for the BC, am I right? Thank you for your help, Adrien

 June 8, 2020, 05:20 #2 New Member   Shreesh Join Date: Dec 2018 Posts: 2 Rep Power: 0 hi Adrien, Do you have any test case that validates wideBandDiffusive boundary condition. In my preliminary test case of square cavity with 1000k walls and internal temperature 1000k,solving for only radiation equation with muti band absorption model. The heat flux at wall is erroneous as wall heat flux is not zero. Pls suggest any changes if you have encountered any bug in this boundary condition. Seeking for your help, Shreesh Last edited by Shreesh; June 8, 2020 at 06:52.

 Tags boundary condition error, radiation fvdom, wideband