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Radiation at interface between fluid and porous domain

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Old   June 8, 2010, 13:57
Exclamation Radiation at interface between fluid and porous domain
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Dear CFX experts, I need help!

I try to model a reactor which consists basically of a porous a fluid and a solid domain. Because I've to deal with very high temperatures radiation is very important. I use the Monte Carlo Model to simulate the radiation inside the fluid and the solid domain. From my point of view I don't need to simulate the radiation heat transfer through the porous media, I consider it by an increased thermal conductivity. But what happens at the interface between porous and fluid domain. Is the porous domain emitting radiation inside the fluid domain and absorbing radiation? When I enable the Beta features it says that the 'opaque' option for non-wall boundary types is enabled.

It would really help me a lot if anyone knows the answer!

Regards,
Philipp
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Old   June 8, 2010, 14:56
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First, you said you had radiation inside the solid domain. Is it glass, or some other transparent media? If not, turn off radiaiton inside the solid domain since it cannot travel through it.
Radiation does not interact with a porous domain. So if you have radiation turned on inside the porous domain, radiation just sees this as a fluid domain and will pass straight through it. If you have radiation turned off inside the porous domain, then I think the fluid-porous interface is just seen as opaque by the radiaiton, so there's no emission of radiaiton by hot porous media (or absorbtion). So there's currently no way to allow porous media and radiation to interact correctly.
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Old   June 8, 2010, 15:24
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Dear Stumpy, thank you very much for your answer.

If I want to simulate the heat transfer in a fluid domain between two solid domains at different temperatures (opaque solids), I don't need a radiation model in the solid domains? Is CFX able to simulate the radiation heat transfer from one solid domain to the other (emitted and absorbed radiation)?

Regards,
Philipp
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Old   June 8, 2010, 18:34
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Quote:
If I want to simulate the heat transfer in a fluid domain between two solid domains at different temperatures (opaque solids), I don't need a radiation model in the solid domains?
If radiation is a significant source of heat transfer then you need it. If not you don't.

Quote:
Is CFX able to simulate the radiation heat transfer from one solid domain to the other (emitted and absorbed radiation)?
Yes.
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Old   June 9, 2010, 02:41
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Dear Glenn,

Thank you very much for your answer! So CFX is only able to treat the radiative heat exchange between a fluid and a solid domain (opaque) correct if in both domains a radiation model is enabled. Is that correct?

Many thanks and regards,
Philipp
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Old   June 9, 2010, 06:25
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Yes. If the solid is transparent then enable radiation in the solid and the radiation can penetrate the solid. If the solid is opaque then radiation interacts with the external interface only, by absorbing and emitting radiation.
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Old   June 9, 2010, 07:47
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Glenn, thank you very much!!
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Old   June 10, 2010, 05:01
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Just one more question:
My solid material is opaque, I just want to model interaction at the surface, is it correct to use in this case the option surface to surface? Or should I choose participating media and define the radiation properties (absorption coefficient...) in the material definitions?

Thank you very much
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Old   June 10, 2010, 08:05
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If the material is opaque then turn the radiation model off in that domain. Then it does not matter what radiation properties you define.
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Old   June 10, 2010, 09:11
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I'm still not sure if I got it correct:

In the case of opaque solid domains, radiation models inside the solid domains are not needed to simulate the radiative interaction between a fluid and a solid domain (emitted and absorbed radiation at the interface of the solid and fluid domain)? I just need to enable a radiation model in the fluid domain? I'm only interested in what happens at the surface of the solid domain. I don't want to simulate the radiative heat transfer through the solid.

Radiation models inside the solid domains are only needed to simulate the radiative heat transfer inside the solid? Is that correct?

I'm sorry to ask you that many questions...

Thank you and regards,
Philipp
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Old   June 10, 2010, 18:23
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Yes, you are correct. If you turn off radiation in the solid then heat transfer will still occur in the solid, but just by conduction. The radiation will only affect the outer surface.
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Old   June 11, 2010, 09:56
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Glenn, thank you very much! You helped me a lot!
Philipp
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Old   June 15, 2010, 06:20
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Thanks Glenn, it helped me very much too.

Last edited by eto; June 15, 2010 at 08:07.
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