The inner and outer surfaces of a 25-cm-thick wall in summer are at 27°C and 44°C, respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40°C, and convection with ambient air also at 40°C with a convection heat transfer coefficient of 8 W/m²·K. Solar radiation is incident on the surface at a rate of 150 W/m². If both the emissivity and the solar absorptivity of the outer surface are 0.8, determine the effective thermal conductivity of the wall.

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150 W/m? 27°C 44°C as = E = 0.8 alr and surroundings, 40°C h= 8 W/m?.K