combination of convection and conduction help

Hello

I want to analyze flat plate and air around the plate.

Laser make heat on the plate. Air gun shot the plate for cooling. It happens in a big hexahedron.

Above all, I want to know how to analyze air around the plate.

I made a big hexahedron, 5m*5m*5m, a plate, 1m*1m*1m.

And used physic model conjugate heat trans-laminar.

Set the hexahedron as fluid, the plate as solid.

Inlet boundary to upper side for air gun. Initial condition is that solid is 400K, fluid is 250K.

Air come in inlet boundary, and it will cool the plate.

Initial condition is that solid is 400K, fluid is 250K.

Then, we can expect that convection occur at surface of the plate, and conduction also occur in the plate, right?

But when I computed it time dependently,
it made error and temperature didn't show the change of temperature of air.

How can I correct it??
How can I see result of the combination?