2. (b.. The inner and outer surfaces of a 25-cm-thick wall are at 27 o C and 45 o C, respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40 o C, and...

2.

(b..

The inner and outer surfaces of a 25-cm-thick wall are at 27
^oC and 45
^oC, respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40
^oC, and convection with ambient air at 42
^oC with convection heat transfer coefficient of 9.0 W/m²
K. Solar radiation incident on the surface is at a rate of 150 W/m². If the emissivity and the solar absorptivity of the outer surface are 0.75 and 0.85, respectively:

(iv)

calculate the radiation heat flux;

(v)

calculate the effective thermal conductivity of the wall.