Question - The wall of a furnace is made up of 250 mm of fire brick, k = 1.05 W/mK; 120 mm of insulation brick, k = 0.85 W/mK, and 200 mm of red brick, k = 0.85 W/mK. The inner and outer surface temperatures of the walls are 850°C and 65°C respectively. Calculate the temperatures at the contact surfaces. Neglect the resistance of mortar joints.