3) either you work with pave, or you try to get quad-map
For that you can for instance split your surface like that
Attachment 22945
And then of course you have 9 surfaces as source + the opposite one

Ah ok, perfect!!!
Now I insert BC, that is:
1)I specify a specific continuum (solid)
2)I specify boundary tipes, that is face with Temperature Ta and face with temperature Tb (as in first post attachment).
The face opposite to displayed face has temperature Ta, displayed face and upper face of parallelepid have Tb. Lateral faces don't care.
ok?
Heat transfer is perpendicular to plate, that is a simple Fourier Equation:
q=k/x*A+(Ta-Tb)
k by material
x by model, it is thickness
A is area
But fluent don't calculate right flux, it seems that there is no flux.
I must insert another BC with this subdivision, maybe on face in common?
The 2 volumes are connected...

Ok remove all!!
I'm really tired!!!
I forgot 1 volume :D
End of problem!!!

Thank you very much Max!!!!!
:-)