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-   -   UDF for a constant heat flux minus radiation based on face temperature (https://www.cfd-online.com/Forums/fluent-udf/149847-udf-constant-heat-flux-minus-radiation-based-face-temperature.html)

MarioArias March 9, 2015 23:08
UDF for a constant heat flux minus radiation based on face temperature
 
I am trying to write a UDF which takes a total constant heat flux boundary condition, but also accounts for the radiative loses. I would like it to use the local face temperature to determine the net heat flux that should be applied at that node face.

If this is possible I would greatly appreciate some information.

Or if there is a better way of accounting for surface-to-ambient radiative loses, I would gladly take that advice.

Thanks,
Mario

vasava March 10, 2015 08:14
If I am not wrong, there are no macros for obtaining radiation related information on node, cell or face. You may have to manually process data exported from Export-->Solution Data option.

MarioArias March 10, 2015 09:21
What about using temperature?
 
Thanks for you reply.

I understand there is no radiation information, but couldn't I simply use the following equation in the UDF:

Q''_{net} = Q''_{total} - \epsilon\sigma(T_{face}^{4}-T_{ambient}^{4})

There must be a simple way to calculate the effects of surface-to-ambient radiation when applying a heat flux, it is such a basic concept.

I must be missing something.

Thanks again,
Mario Arias

`e` March 10, 2015 15:54
You could use your own calculation for radiation losses inside a custom boundary condition using a DEFINE_PROFILE macro. Loop through the faces using begin_f_loop and end_f_loop. The face temperature could be found with F_T(f,t) and the ambient temperature could either be found in another cell zone (if you are simulating the surrounding environment) or hard coded.


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