A composite plane wall consists of a Li = 125 mm thick layer of insulation (ki = 0.05 W/m.K) and a Ls = 25 mm thick layer of siding (ks = 0.10 W/m.K). The inner temperature of the insulation is 20 C. The outer temperature of the siding is -10 C. Steady state conditions apply.
​
​Determine the temperature at the interface between the two layers, in C, and the rate of heat transfer through the wall, in W per m2 of surface area.