A horizontal, opaque surface at a steady-state temperature of 80°C is exposed to an airflow having a free stream temperature of 25°C with a convection heat transfer coefficient of 20 W/m2 ·K. The emissive power of the surface is 628 W/m2 , the irradiation is 1380 W/m2 , and the reflectivity is 0.30.

Determine the absorptivity of the surface.

Determine the net radiation heat transfer rate for this surface. Is this heat transfer to the surface or from the surface?

Determine the com-bined heat transfer rate for the surface. Is this heat transfer to the surface or from the surface?