Flow Simulation with NO fluid solving

I have a simple assembly and want to look at heat transfer within.

I know the external surfaces will lose heat at 12 w/m2k, so...no external flow solution needed

There is a small internal cavity with air, but it's so small that conduction is all that matters....no internal flow solution needed. I define a part for that air space, and apply the 'solid' properties of air.

In general settings I specify internal flow solution, and turn on conduction in solids.

The computational domain properly locks coincident with the orthogonal external surfaces.

Now my troubles begin.

I can't assign the external faces and apply 12 w/m2k. I suspect this is because the computational domain is coincident, because if I run an external flow solution, and the computational domain is external of these surfaces, I can pick the surfaces and assign an h. Not always BTW.

If I avoid any external BCs, the tool then complains about leaks. This is interesting since everything inside the computational domain is a solid as I've defined it. Even the air is just a solid with air's thermal conductivity.

I know this is a fluid solving tool, but shouldn't we be able to 'turn off momentum' equations in the solver?

Can SW Flow Simulation be used for conduction and radiation only problems?

How?

Thanks,

John