A steel tube [k = 15 W/(m.°C)] of outside diameter 7.6 cm and thickness 1.3 cm is covered with an insulation material [k = 0.2 W/(m.°C)] of thickness 2 cm. A hot gas at 320°C with a heat transfer coefficient of 200 W/(m2.°C) flows inside the tube. The outer surface of the insulation is exposed to cooler air at 20°C with a heat transfer coefficient of 50 W/(m2.°C).
Calculate
a) The heat loss from the tube to the air for a 5-cm length of the tube.
b) The temperature drops due to the thermal resistances of the hot gas flow, the steel tube, the insulation layer, and the outside air.