# Radiation modelling in CFD

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February 2, 2021, 02:40
Radiation modelling in CFD
#1
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Asher
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Consider a problem of flow over a sphere inside a cylindrical conduit. The cylinder has a heated wall, and conjugate heat transfer occurs between the cylinder wall and the gas flowing inside, further, there is conjugate heat transfer between the gas and the sphere over which it is flowing. (Ref. attached figure)

In reality, apart from the above-stated heat transfer, there is radiation heat transfer from the cylinder wall to the sphere. How do I go about modelling the same in CONVERGE??

I have referred to the manual; the discussion over there is quite brief.
Attached Images
 Rad.jpg (32.2 KB, 24 views)

February 2, 2021, 09:50
#2
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John Etcheverry
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Quote:
 Originally Posted by mohmdasher Consider a problem of flow over a sphere inside a cylindrical conduit. The cylinder has a heated wall, and conjugate heat transfer occurs between the cylinder wall and the gas flowing inside, further, there is conjugate heat transfer between the gas and the sphere over which it is flowing. (Ref. attached figure) In reality, apart from the above-stated heat transfer, there is radiation heat transfer from the cylinder wall to the sphere. How do I go about modelling the same in CONVERGE?? I have referred to the manual; the discussion over there is quite brief.
Hi Asher! Am I correct in that you are you just looking for assistance with the radiation model? Do you have any specific questions regarding it? I understand what you're trying to create, I'm just trying to understand where things are going wrong for you with it.

Also, what version of CONVERGE are you working with?

Thanks,

- John
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John Etcheverry
Research Engineer
CONVERGECFD

February 2, 2021, 12:03
#3
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Asher
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Quote:
 Originally Posted by jetcheve Hi Asher! Am I correct in that you are you just looking for assistance with the radiation model? Do you have any specific questions regarding it? I understand what you're trying to create, I'm just trying to understand where things are going wrong for you with it. Also, what version of CONVERGE are you working with? Thanks, - John
Thank you for the reply John.

Yes, I am looking for some inputs regarding the radiation model. The specific question would be; how do I define as to which surface is emitting the radiation and which surface is absorbing it. In the case of CHT, I have a forward side and a reverse side, how do I define boundaries in case of radiation?

I'm working with Converge 3.0.

Thank you,
Asher

February 3, 2021, 13:46
#4
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John Etcheverry
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Quote:
 Originally Posted by mohmdasher Thank you for the reply John. Yes, I am looking for some inputs regarding the radiation model. The specific question would be; how do I define as to which surface is emitting the radiation and which surface is absorbing it. In the case of CHT, I have a forward side and a reverse side, how do I define boundaries in case of radiation? I'm working with Converge 3.0. Thank you, Asher
Great - thanks! So, I think what you're looking for is in the radiation modeling window under the boundaries tab: rad_boundaries.png.

Here you can define the radiation properties of each boundary, or in the case of CHT, you can choose forward or reverse side of the interface boundary.

As for specifying what absorbs and what emits this is going to be based upon the temperatures of your boundaries as well as the properties you set up in the boundaries tab of the radiation model one you turn it on.

Let me know if I can be of any help with further questions you may have.

- John
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John Etcheverry
Research Engineer
CONVERGECFD

February 3, 2021, 23:38
#5
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Asher
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Quote:
 Originally Posted by jetcheve Great - thanks! So, I think what you're looking for is in the radiation modeling window under the boundaries tab: Attachment 82511. Here you can define the radiation properties of each boundary, or in the case of CHT, you can choose forward or reverse side of the interface boundary. As for specifying what absorbs and what emits this is going to be based upon the temperatures of your boundaries as well as the properties you set up in the boundaries tab of the radiation model one you turn it on. Let me know if I can be of any help with further questions you may have. - John
Thank you, John.

Previously too I did reach the point till the radiation boundary window. However, what I was not clear with is;
1. Do I need to select all the boundaries? Since all the boundaries are subjected to radiation.
2. Do I need to specify which boundary emits/absorbs? From your previous reply, I have understood that I just need to provide the properties and temperature; and converge will decide the nature of radiation, please correct me if I am wrong.

Thanks,
Asher

February 4, 2021, 16:00
#6
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John Etcheverry
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Quote:
 Originally Posted by mohmdasher Thank you, John. Previously too I did reach the point till the radiation boundary window. However, what I was not clear with is; 1. Do I need to select all the boundaries? Since all the boundaries are subjected to radiation. 2. Do I need to specify which boundary emits/absorbs? From your previous reply, I have understood that I just need to provide the properties and temperature; and converge will decide the nature of radiation, please correct me if I am wrong. Thanks, Asher
Asher -

1 - No, just select the boundaries you expect to be involved in radiative heat transfer. If all, then yes, select all boundaries.
2 - You do not need to specify which boundaries emit and absorb. Your understanding of this is correct.
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John Etcheverry
Research Engineer
CONVERGECFD

February 5, 2021, 00:56
#7
New Member

Asher
Join Date: Jun 2020
Posts: 18
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Quote:
 Originally Posted by jetcheve Great - thanks! So, I think what you're looking for is in the radiation modeling window under the boundaries tab: Attachment 82511. Here you can define the radiation properties of each boundary, or in the case of CHT, you can choose forward or reverse side of the interface boundary. As for specifying what absorbs and what emits this is going to be based upon the temperatures of your boundaries as well as the properties you set up in the boundaries tab of the radiation model one you turn it on. Let me know if I can be of any help with further questions you may have. - John
Quote:
 Originally Posted by jetcheve Asher - 1 - No, just select the boundaries you expect to be involved in radiative heat transfer. If all, then yes, select all boundaries. 2 - You do not need to specify which boundaries emit and absorb. Your understanding of this is correct.
Thank you for all the help.

Regards,
Asher

February 18, 2021, 23:43
#8
New Member

Asher
Join Date: Jun 2020
Posts: 18
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Quote:
 Originally Posted by jetcheve Asher - 1 - No, just select the boundaries you expect to be involved in radiative heat transfer. If all, then yes, select all boundaries. 2 - You do not need to specify which boundaries emit and absorb. Your understanding of this is correct.
Hi John,

Can I define radiation heat transfer on a CHT boundary (interface)?

Thanks,
Asher

February 22, 2021, 13:10
#9
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John Etcheverry
Join Date: Dec 2018
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Quote:
 Originally Posted by mohmdasher Hi John, Can I define radiation heat transfer on a CHT boundary (interface)? Thanks, Asher
Asher - if you're defining a heat transfer condition on a fluid-solid interface, you would no longer be running a CHT. A fluid-solid interface in CHT means the energy equation is coupled across the interface from the fluid to the solid domains so you cannot prescribe a heat transfer boundary condition other than coupled. If you just want the CHT solid to be emitting and absorbing you can specify the fluid facing side of the boundary in the radiation modeling panel the way we discussed previously.

Happy CFDing!

- John
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John Etcheverry
Research Engineer
CONVERGECFD

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