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Ceramic foam exposed to concentrated radiation |
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July 17, 2013, 10:42 |
Ceramic foam exposed to concentrated radiation
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#1 |
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Philipp
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Hi everybody!
I'm modeling the heat-up behavoir of a ceramic foam exposed to concentrated radiation. At the same time the foam is penetrated by a gas flow. The foam is modeled as a porous domain (fluid and solid) which is placed between two fluid domains. Problem discription: Radiation which penetrates into the foam interacts only with the fluid in the porous domain (if participating media is selected, otherwise no interaction) and not with the solid. In reality radiation is absorbed by the solid part which afterwards heats up the fluid. From my point of view this is implemented incorrectly in CFX. Question: Does anybody know if there is a way to add interaction of radiation with the solid part of the porous domain? |
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July 17, 2013, 18:46 |
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#2 | |
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Glenn Horrocks
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Does the radiation only interact with the front face of the ceramic? Do you need to model the radiation or can it be modelled as simply a heat source? Is the fluid passing through the ceramic transparent (or close to it)? |
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July 18, 2013, 03:52 |
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#3 | |||
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Philipp
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Hi Glen, thanks for your reply!
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Best, Philipp |
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July 18, 2013, 08:59 |
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#4 |
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Glenn Horrocks
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What version of CFX are you using?
I think heat transfer in porous domains was only included in V14. |
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July 18, 2013, 09:10 |
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#5 |
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Philipp
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July 18, 2013, 19:01 |
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#6 |
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Glenn Horrocks
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OK, so you have a version of CFX which supports heat transfer between the solid and fluid phases in a porous domain - so far so good.
I am not sure the radiation is supported per se in the solid phase in a porous domain. You will need to investigate this. You will certainly need the monte carlo model if it is supported, the other radiation models will not handle this. Another thought - Does the radiation change? Or is it coupled to the fluid or ceramic in some way? You might also be able to apply the radiation heat load as a volumetric heat source on the porous domain and not directly model the radiation at all. |
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August 3, 2013, 12:39 |
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#7 |
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Philipp
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Hi Glen,
Thanks for your answer.
=> if I do so, I have radiation models in the adjacent fluid domains but non in the porous domain (pls see picture attached). I'm worried about what happens with the radiation part at the interfaces of fluid-porous-fluid. What do you think? |
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August 4, 2013, 07:20 |
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#8 |
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Glenn Horrocks
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I cannot see how changing the thermal conductivity of the material can be a substitute. You are replacing a radiation heat load with a change in thermal conductivity. They are totally different things.
Also your picture was not attached. Some questions: How far into the porous material does the radiation penetrate? Just the surface? Or a significant distance inside? If it penetrates, how - is the porous material partially transparent or is it very sparse? I think there will be a few ways to work around this, I just need to understand what you are doing a little better. |
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August 4, 2013, 08:42 |
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#9 | ||||
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Philipp
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Reference: Laubitz, M., Thermal Conductivity of Powders. Canadian Journal of Physics, 1959. 39(7): p. 11. Quote:
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August 4, 2013, 09:07 |
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#10 |
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Glenn Horrocks
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So how about this: If CFX ignores radiation in the solid part of the porous region, then how about you use an elevated absorption coefficient in the fluid in the region of the porous material. This models the additional radiation captured by the solid materail compared to the fluid. And for the re-radiated stuff (if this is significant enough to need to be modelled) you can use a radiation source term to generate radiation from the porous material, although it will actually be a source term on the fluid in the porous region.
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August 4, 2013, 09:22 |
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#11 |
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Philipp
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I agree, this could work. From my point of view including a source term to account for emitted radiation is not even needed becasue CFX should also account for that. If participating media for the fluid part in the porous domain is selected then CFX accounts for absorption, scattering and emission. Do you agree?
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August 4, 2013, 18:05 |
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#12 |
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Glenn Horrocks
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Why do you say the source term for emitted radiation should not be needed? The solid component of the porous material does not participate in the radiation model, so if you want to include the emitted radiation from the porous material you are going to have to have a source term to include it.
Is the fluid totally transparent? Or does the fluid have some absorbance, scattering or emission? |
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August 5, 2013, 03:12 |
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#13 | ||
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Philipp
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Hi Glenn, thank you very much for your reply. Maybe I'm still not understanding your approach correctly.
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August 5, 2013, 06:56 |
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#14 |
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Glenn Horrocks
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I would check the effect of using a fluid-solid HTC to account for the radiation emmission of the solid. I do not think it will model the real situation too well. At least with a emmission source term you can put factors in there to make it representative of the solid temperature and get the emmission closer to reality.
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