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°c. 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