Air flows at 120°C in a thin-wall stainless-steel tube with h = 65 W/m2 · °C. The inside diameter of the tube is 2.5 cm and the wall thickness is 0.4 mm. k = 18 W/ m · °C for the steel. The tube is exposed to an environment with h = 6.5 W/m2 ·°C and T8 = 15°C. Calculate the overall heat-transfer coefficient and the heat loss per meter of length. What thickness of an insulation having k = 10 mW/ m · °C should be added to reduce the heat loss by 90 percent?