3-88 In a pharmaceutical plant, a copper pipe (ke= 400 W/m-K) with inner diameter of 20 mm and wall thickness of 2.5 mm is used for carrying liquid oxygen to a storage tank.The liquid oxygen flowing in the pipe has an average temperature of -200°C and a convection heat transfer coefficient of 120 W/m².K. The condition surrounding the pipe has an ambient air temperature of 20°C and a combined heat transfer coefficient of 20 W/m². K. If the dew point is 10°C, determine the thickness of the insulation (k; = 0.05 W/m-K) around the cop-per pipe to avoid condensation on the outer surface. Assume thermal contact resistance is negligible.