Impose a boundary condition on an interface between a solid and a fluid
 

I seek to impose a boundary condition on an interface between a solid and a fluid ???

plzzz help me

I Guess a solid-fluid interface would simply be a wall? What is the problem with applying a boundary condition there?

Or are you using a solid zone and fluid zone? If so - why; why not just leave out the solid part, and make the interfaces walls?

thank you CeesH for your reply, I explain my problem:
I want to simulate a solar receiver. we have two coaxial tubes.
the inner tube of length = 3m, it is made of steel it has a thickness = 3mm and receives a solar flux = 8000 W.
the outer tube is made of glass.

==> Be simulated, the convective thermal exchanges between the internal tube and the area of the cavity ???
When I use ansys fluent, I find the problem of creating a shadow face of the outer face of the inner tube, which I must impose a condition (flux = 8000W) !!!

Is what I will impose the boundary condition on the outer surface of the tube or on shadow face ???