I'm trying to solve a conjugate heat transfer problem using the convection-diffusion equation. The laminar flow contributes to the heat transfer problem through the variable u in the Eq. 1. For the heat transfer, there is a Dirichlet BC at the bottom and the rest are zero flux.
0=∇.(α∇T)-∇.(uT) Eq.1
My issue is that, with the convection-diffusion equation, the temperature gradient inside the domain is extremely low close to zero. I solved the same problem using the heat transfer module and I get a completely different result. Given that the BCs and the equation in both cases are identical, where is the problem? I've attached the mph file and appreciate any help.