problems in the interaction between solid to fluid domains in fluent
 

I'm doing a cooling simulation of an electric motor that uses a water cooling system. but it seems there is a problem between solid to fluid domain interactions. where when heat flux is applied to the solid domain and propagates to the fluid domain, the results are invalid. but when my inter-domain connection is broken and heat flux is applied to the fluid domain, the result becomes valid
Does anyone know how to maximize heat transfer between solid and fluid domains so that the Nusselt number results are valid?

When you say invalid do you mean "do not match expirement/calculation" or the solution is not converging? I would check to make sure that your wall between the two fluids is set as a coupled wall. I would also make sure your boundary layer refinement in the fluid domain is adaquete to capture the heat transfer correctly.

incorrect here is not in accordance with the validation or experimental equation. then each domain is connected as a coupled wall and there is heat transfer between domains, but the value of the Nusselt number is still not correct.

for example, on Re 500, the fluid outlet temperature is correct, but the wall temperature is still wrong, what should be 109 C, I got 138 deg C instead, so the Nusselt value should be 12, I got 5 instead.

if each domain has a coupled wall and heat transfer has occurred, then where might the problem occur? for the record I've tried smoothing the mesh for the fluid domain