# P1 Multiband absorption coefficient

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 August 8, 2016, 04:44 P1 Multiband absorption coefficient #1 New Member   Lukas Join Date: May 2016 Location: Germany Posts: 19 Rep Power: 9 Hey, I want to simulate radiation in air with the P1 multiband model. In the fluid domain I activated radiation and selected the P1 model, then I changed the spectral model to multiband. I want to divide the spectral lines in 6 bands and apply for each band an absorption coefficient. How do I change the absorption coefficient of these bands with CEL? Thank in advance for your response. Best Greetings Lukas

 August 8, 2016, 11:14 #2 Senior Member   Join Date: Jun 2009 Posts: 1,803 Rep Power: 32 You can create an interpolation function between the absorption coefficient and the wavelength in vacuum, or frequency. You can create a CEL expression for the absorption coefficient as a function of wavelength or frequency using step functions. Hope the above helps,

 August 10, 2016, 08:43 #3 New Member   Lukas Join Date: May 2016 Location: Germany Posts: 19 Rep Power: 9 Thank you very much Opaque! I was now able to implement the radiation model. I get a notice that the contribution to the spectrum is negligible for some spectral bands. To specify for every band except the band with the lowest frequency. +--------------------------------------------------------------------+ | ****** Notice ****** | | Spectral band contribution to the spectrum is negligible | | Domain : Fluid Domain | | Spectral Band: Spectral Band 4 | | Contribution : 0.60135-153 | +--------------------------------------------------------------------+ Do you know if this is a problem? The radiation is calculated for these bands and the simulation is convergent. Even in a file provided by Ansys i found this notice. Kind regards

 August 20, 2016, 11:54 #4 New Member   Lukas Join Date: May 2016 Location: Germany Posts: 19 Rep Power: 9 Hey, first, as an extra information, it is important to set the emission factor for the wall boundaries for each band as well. Concerning my problem: It is not a problem, just a notice. I implemented the bands for radiation for up to 30000 K so that if i initialize my setup with 300 K, the intensity isn't high enough. You can negligate this information, if you are shure, that your setup will reach higher temperatures, otherwise you should change your bands frequency.

 Tags absorption coefficient, multiband, p1 radiation