heat flow UDF on coupled surface (wall-shadow wall)
 

Hallo!

i'm relative new to UDF programming and i would need a little help!

i have a fluid-solid-fluid problem (air-pipe-steam). the case works fine with coupled wall implemented in fluent. Now i'm trying to implement an UDF in order to calculate myself the heat flux through the pipe (i have variable thickness and k). I designed an UDF that solve one dimensional Fourier equation (since the thickness is low, infinite slab approximation is ok i think).
I obtain the value of the temperature for both air and steam side faces and then i calculate the heat flux with DEFINE_EXCUTE_AT_END. i write the value in a file *.txt. then the DEFINE_PROFILE reads the file and assign the heat flux previosly calculated on both external and internal surface (with the right sign) for the new iteration.
My question is: is this procedure right (apart from optimization)? i keep on having divergence (the heat flux goes high! ) as i assign the UDF in the boundary condition panel in FLUENT.

Thanks in advance