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How to simulate a porous media which is opaque to thermal radiation in Fluent Ansys?

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Old   June 2, 2020, 11:33
Default How to simulate a porous media which is opaque to thermal radiation in Fluent Ansys?
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Hello

I am trying to model a porous zone in Fluent (the fluid in void is air) which is opaque to thermal radiation. If I set it as a porous zone with air as the media, Fluent treats it as a transparent zone and the thermal radiations do not interact. The zone is only opaque if I set it as a solid zone (with boundary condition set to wall), however in this case air won't flow through it. The aim is to simulate a porous zone within a larger domain.

Is there a way to combine them, to model a zone which is porous while also being opaque to thermal radiation (something like a sponge, opaque to thermal radiation but allows airflow through it).

Thanks
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Old   June 2, 2020, 11:38
Default Opaque Region
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A porous region in Fluent is fluid region. And to make it opaque, just set its absorption coefficient to 1.
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Old   June 2, 2020, 11:47
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You mean changing the absorption coefficient of the fluid?
So, in this case, it is air, since it is a porous zone. But then the entire domain becomes that as the fluid is air throughout.
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Old   June 2, 2020, 11:51
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Dry air does not participate in radiation, i.e., its absorption and scattering coefficient are very very low. However, a porous zone consists of two domains, a solid and a fluid. As long as you use equilibrium model, i.e., assumption of same temperature for fluid and solid, you need to modify absorption coefficient of the air as well as that of the solid material representing the solid region. If you use non-equilibrium model, then you can change material properties only for the solid region.
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Old   June 2, 2020, 12:08
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I am using an equilibrium model for heat transfer (see image). However I don't see the option to change the absorption coefficient of the solid material.

As for the fluid, I created a copy of 'air' and set its absorption coefficient (AC) to 1. So the air in the domain has AC set to 0 and air in the porous zone has AC set to 1. Am I doing it correctly?
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Old   June 2, 2020, 12:12
Default Radiation Parameters
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Which radiation model are you using?
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Old   June 2, 2020, 12:15
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P1, solar loading (see image)
What do you suggest can be done?
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Old   June 3, 2020, 09:29
Default Radiation Model
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In case of P1, radiation properties are not required for solid. Solids are opaque to the radiation in the sense that they block it.
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Old   June 3, 2020, 11:55
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But my porous zone is not behaving like that. It is totally transparent to the solar radiation. I have made sure to check the 'participate in radiation' option for that zone too.
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Old   June 3, 2020, 12:27
Default Absorption Coefficient
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Despite using an absorption coefficient of 1. Do note that an absorption coefficient of 1 also implies emission coefficient of 1. So, the fluid zone may not be transparent but emitting the radiation.
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Old   June 3, 2020, 12:34
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How do I overcome this?

Simply put, I have a porous zone within a larger domain. The fluid is air flowing in the region. Solar radiation is activated. The aim is to investigate the impact of wind speed and porosity on the temperature around the porous zone.
Don't want to spend too much time and effort modeling it on Fluent, an approximate model is fine.
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Old   June 3, 2020, 13:13
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If it is only solar radiation, then you don't need to enable radiation model. Solar radiation is different and can be used exclusive of radiation model.
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Old   June 4, 2020, 06:04
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Hi
I have updated the settings based on your suggestion (see image). However, I see no impact of this. My porous zone is still transparent to the solar radiation.

Can I upload my file here for you to have a look?

Thanks
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Old   June 4, 2020, 06:09
Default Transparency
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How are you determining that the zone is transparent? If the radiation model is turned off, there is no question of transparency or opaqueness.
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Old   June 4, 2020, 06:15
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I have attached a snapshot of the model. Since there is 0 solar radiation on the porous region and all of it passes through onto the ground, it means that the porous zone is transparent to the solar radiation.
What I am trying to achieve is that this porous zone will cast a shadow, since it will block the solar radiation. I need to use a porous zone in this case because the air is still flowing through it.
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Old   July 1, 2020, 10:00
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Some help here will be appreciated.

Thank you
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