Calculate incoming temperature to a wall
 

Hi:

I'm performing a free convection model including heat transfer effects. I need to know the temperature of the the flow adjacent to a flow but without impossing the temperature of the wall,which is unknown, neither the heat flux, which is unknown, neither using the convective heat transfer coeficient,which is unknown as well. As you can see i'm trying to find the temperature that the wall has to withstand.

The problem is even more complicated because i have to include radiation effects but that doesn't matter until i can't solve the foregoing.

What boundary condition is the more appropriate?. Any idea?

Thanks in advance.