[MNMK]

Hi everybody,

I would like to calculate the radiation heat transfer in Post. Normally, through areaInt(heat Flux)@ Location, I am able to calculate total heat Flux. I would like to know how it is possible to calculate the radiation portion for example in a domain or interface etc. Is it possible at all? I have found the quantities ''Wall Irradiation Flux" and "Wall Absorbed Radiation Flux'' which I don't know whether they are trustable values and what do they calculate exactly in post??!!

wishes,

[Opaque]

Your question is incomplete, which may explain your confusion with the different variables. For starters: CFD-Post does not compute any of them, only post-process the results from the Ansys CFX Solver.

Heat Flux = Convective Heat Flux + Radiation Heat Flux

Radiation Heat Flux = Incoming Radiative Heat Flux - Outgoing Radiative Heat Flux

Incoming Radiative Heat Flux = Integral over the hemisphere of radiation coming from anywhere projected over the surface --> Irradiation Flux

Outgoing Radiative Heat Flux = Emitted Radiative Heat Flux + Reflected Radiative Heat Flux

I will leave it at this point since I think you should be able to complete the rest from here.

[ghorrocks]

I will add that I recommend you do a small benchmark case, with two surfaces of known temperature so the heat transfer is a simple analytical equation. Model this and make sure you can get the correct radiative heat transfer. And then in the post processing you can see what all the radiation heat transfer variables represent.

[MNMK]

Originally Posted by ghorrocks

I will add that I recommend you do a small benchmark case, with two surfaces of known temperature so the heat transfer is a simple analytical equation. Model this and make sure you can get the correct radiative heat transfer. And then in the post processing you can see what all the radiation heat transfer variables represent.

Hi Ghorrocks,

It seems a good idea. Thanks a lot.

[MNMK]

Originally Posted by Opaque

Your question is incomplete, which may explain your confusion with the different variables. For starters: CFD-Post does not compute any of them, only post-process the results from the Ansys CFX Solver.

Heat Flux = Convective Heat Flux + Radiation Heat Flux

Radiation Heat Flux = Incoming Radiative Heat Flux - Outgoing Radiative Heat Flux

Incoming Radiative Heat Flux = Integral over the hemisphere of radiation coming from anywhere projected over the surface --> Irradiation Flux

Outgoing Radiative Heat Flux = Emitted Radiative Heat Flux + Reflected Radiative Heat Flux

I will leave it at this point since I think you should be able to complete the rest from here.

Dear Opaque,

My meaning was in the Post Processing. Perhaps I called it wrongly. Let me explain more. I have a model which I simulated. My aim was first, to evaluate the heat flux in the system. As I said , through the mentioned expression, it is possible to calculate the heat flux. My next goal is calculating the portion of radiation in the total Heat Flux. Your explanation was exact, which I could guess. But I would like to know if the quantities such as ''Wall Irradiation Flux" and "Wall Absorbed Radiation Flux'' are suitable or I shoud find other way to calculate the radiation portion? Specially when they call with Wall ... . As I know and see in my results there is a different between the value of Wall Heat Flux and Heat Flux.

regards,

[Opaque]

Originally Posted by MNMK

Dear Opaque,

My meaning was in the Post Processing. Perhaps I called it wrongly. Let me explain more. I have a model which I simulated. My aim was first, to evaluate the heat flux in the system. As I said , through the mentioned expression, it is possible to calculate the heat flux. My next goal is calculating the portion of radiation in the total Heat Flux. Your explanation was exact, which I could guess. But I would like to know if the quantities such as ''Wall Irradiation Flux" and "Wall Absorbed Radiation Flux'' are suitable or I shoud find other way to calculate the radiation portion? Specially when they call with Wall ... . As I know and see in my results there is a different between the value of Wall Heat Flux and Heat Flux.

regards,

The differences between Wall Heat Flux and Heat Flux, if I recall correctly, are documented. The Ansys CFX solver boundary-only quantities such Wall Shear, Wall Heat Flux, etc involve some averaging around boundary mesh vertices that introduce slight inconsistencies. The Heat Flux variable is the exact quantity from the solution step and once areaInt(Heat Flux)@Boundary will give you the same value as reported in the output file.

If i recall correctly, Heat Flux is the sum of convective and radiation heat flux as well. So, it is perfectly OK to subtract areaInt(Wall Convective Heat Flux)@Boundary from areaInt(Heat Flux)@Boundary to obtain the Radiative
Heat Flow on the boundary.

The other radiation quantities are useful if you want to understand the radiation splits: emission, absorption, etc..

[MNMK]

Originally Posted by Opaque

The differences between Wall Heat Flux and Heat Flux, if I recall correctly, are documented. The Ansys CFX solver boundary-only quantities such Wall Shear, Wall Heat Flux, etc involve some averaging around boundary mesh vertices that introduce slight inconsistencies. The Heat Flux variable is the exact quantity from the solution step and once areaInt(Heat Flux)@Boundary will give you the same value as reported in the output file.

If i recall correctly, Heat Flux is the sum of convective and radiation heat flux as well. So, it is perfectly OK to subtract areaInt(Wall Convective Heat Flux)@Boundary from areaInt(Heat Flux)@Boundary to obtain the Radiative
Heat Flow on the boundary.

The other radiation quantities are useful if you want to understand the radiation splits: emission, absorption, etc..

Dear Opaque,

I appreciate your clear answer. I wish you the bests.

regards,