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Handling of spectral emissivity for radiative heat transfer
Posted 24 mars 2011, 07:15 UTC−4 Heat Transfer & Phase Change, Modeling Tools & Definitions, Parameters, Variables, & Functions 2 Replies
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Hi,
Comsol uses for radiation a gray model. But many materials aren't gray, since their emissivity (strongly) depends on the frequency. As far as I know, ANSYS CFX for example handles this for e.g. using the multiband model, which treats the radiation in terms of a number of spectral bands. It treats each band independently.
Could it be possible to apply this to the current Comsol version?
May be it's possible to use serval general heat transfer modes to compute the contribution of separated spectral bands with their own emissivity, which are finally added (and may be corrected) in one application mode?
Or may be there are other possibilities of handling this issue? Or has Comsol such a feature on it's roadmap?
Who else is interested? At least, this seems to me very important for doing appropriate heat transfer modeling.
Best regards
Comsol uses for radiation a gray model. But many materials aren't gray, since their emissivity (strongly) depends on the frequency. As far as I know, ANSYS CFX for example handles this for e.g. using the multiband model, which treats the radiation in terms of a number of spectral bands. It treats each band independently.
Could it be possible to apply this to the current Comsol version?
May be it's possible to use serval general heat transfer modes to compute the contribution of separated spectral bands with their own emissivity, which are finally added (and may be corrected) in one application mode?
Or may be there are other possibilities of handling this issue? Or has Comsol such a feature on it's roadmap?
Who else is interested? At least, this seems to me very important for doing appropriate heat transfer modeling.
Best regards
2 Replies Last Post 24 mars 2011, 10:53 UTC−4
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Posted:
1 decade ago
Hi
cant you define the emissivity as a function of the wavelength and then integrate over these ?
--
Good luck
Ivar
cant you define the emissivity as a function of the wavelength and then integrate over these ?
--
Good luck
Ivar
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Posted:
1 decade ago
Hi Ivar,
of course you can integrate the emissivity over the frequency.
If you weigh it in relation to black body radiation you get an equivalent emissivity - most of the emissivity valus are in this way averaged values. But you are still using the gray model which assumes a constant emissivity. It is not possible to use frequency dpended emissivities in Comsol. My staring point was, to use serveral Heat transfer modes which treats a single range for frequencies. Then using the dependent variable "J" of the serveral modes and use them in the original HT mode.
Serveral things could be difficult: No Jacobian contribution of the "dummy" modes would be necessary (I guess ...). Corrections when adding "J" to make sure no extra energy comes around. It's a bit of theretical to do ... But could work. ... I have no clue :)
of course you can integrate the emissivity over the frequency.
If you weigh it in relation to black body radiation you get an equivalent emissivity - most of the emissivity valus are in this way averaged values. But you are still using the gray model which assumes a constant emissivity. It is not possible to use frequency dpended emissivities in Comsol. My staring point was, to use serveral Heat transfer modes which treats a single range for frequencies. Then using the dependent variable "J" of the serveral modes and use them in the original HT mode.
Serveral things could be difficult: No Jacobian contribution of the "dummy" modes would be necessary (I guess ...). Corrections when adding "J" to make sure no extra energy comes around. It's a bit of theretical to do ... But could work. ... I have no clue :)