A refrigerant at -40°C flows inside a copper pipe (inside diameter = 3 cm, outside diameter = 3.4 cm) with a convective heat transfer coefficient of 110 W/m2K at the inner surface. To reduce the heat flow into the pipe to 20 W per meter length of the pipe, an insulation (k = 0.04 W/mK) is added to the outside of the pipe. For an ambient air temperature of 25°C and a heat transfer coefficient of 18 WIm2K, at the insulation surface, determine the required thickness of the insulation. Show the thermal circuit and label the temperatures and resistances (mathematical expressions).