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Hello Experts,

I want to ask question and discuss how to make a fast convergence conjugate heat transfer solver.

I am currently using OpenFOAM chtMultiRegionSimpleFoam which is steady state cht solver. The problem is it reaches convergence state very slow compare with commercial software, it could be slow down like 20 times. I believe the reason is OpenFOAM chtMultiRegionSimpleFoam is doing loosely coupled cht, so it solves fluid and solid separately.

I know there are two things to affect the convergence,
one is interface boundary condition, so both fluid and solid side should satisfy temperature Ts=Tf and heat flux Qs=-Qf

The other one how you solve it either you put fluid energy equation and solid energy equation in same matrix like in foam-ext conjugateHeatSimpleFoam, or your solve them separately.
By checking the OpenFOAM coupled boundary condition, it seems satisfy the Qs = -Qf condition, but I think there must be other way to define interface to improve the heat convergence.

So my question is could any expert give me some suggestion to improve the interface bc.

The second question is OF is solved fluid and solid in different matrix and iteratively. Does it a matter to put fluid and solid in same matrix? For me if we have a very good interface bc, how you solve it in same matrix or different matrix should only affect the parallel efficiency, not much on convergence speed?

Looking forward your answers.