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I am solving 3d flow and conjugate heat transfer in a double layered micro-channel. I am considering half of the channel due to symmetry. I have a velocity inlet for both the layers, and a fully developed conditions( both hydro dynamically and thermally) at the outlet, so an outflow at the outlet. I have coupled walls near the solid-fluid interface. I have constant heat flux at the bottom of the channel. Rest all are walls.

I am running a 3d steady, laminar case and the solution is not converging. The mass flow rate is being balanced. SO can anyone let me know where I am going wrong?