[Engineers_Firelli]

Hello,


I'm new on the forum. I'm trying to simulate a hot gas flow through ducts in Code_Saturne. I was wondering how to setup a boundary condition that combines:
* a heat transfer coefficient + outer temperature (representing the convection between the external wall and the ambient)
* an emissivity at the outer wall + outer temperature (representing the radiation from the externall wall to the ambient)


(* perhaps it would be nice also to include the conduction in the wall, but this may be calculated analytically and included in the heat transfer coefficient mentioned above)


1. Using the GUI, I tried different combinations of BC for the temperature scalar and for the thermal radiative heat transfer (I included a P1 radiation model, although I don't want it for the fluid, I just want the radiation from the external wall of the duct to the ambient).


However, the "thermal radiative heat transfer" does not seem to have any effect on the temperature distribution on the wall (the wall does not cool down through radiation), although I tried different emissivities, ambient temperatures, even with a conductivity heat flow.





2. I thought of another idea, to use a user law to define the heat flux or the heat transfer coefficient (and for example use the trick h = h_conv + h_rad, where h_rad = sigma * epsilon * (T_wall^4 - T_ambient^4)/(T_wall - T_ambient) ). However, how can one access the temperature value on the wall patch from the user law definition in the GUI ?? It seems to be possible to access only time and space variables.

If this is only possible through the code, could someone please explain the details of how to do it using the code (how to access the temperature value on the patch and to define the heat flux or the heat transfer coefficient based on the temperature) ?

Thanks in advance.
Theo