Hi @tiannh7,
The motivation behind introducing an internal temperature boundary in my model is to obtain a steady-state temperature field with internal heating , while maintaining a fairly uniform temperature within the mantle .
I confess I’m not sure I fully understand the exact nature of the problem you are trying to setup, but one alternative option worth considering is to use a function with the Heating model plugin. See the this forum post for relevant discussion on this option.
Cheers,
John