Heat Transfer
Composite tube wall: A thin electrical heater (of negligible size) is inserted between a long circular rod and a concentric tube with inner and outer radii of 20 and 40 mm. The rod (A) has a thermal conductivity of kA = 0.15 W/m·K, while the tube (B) has a thermal conductivity of kB = 1.5 W/m·K and its outer surface is subjected to convection with a fluid of temperature T∞ = -10°C and a heat transfer coefficient of 50 W/m^2·K. The thermal contact resistance between the cylinder surfaces and the heater is negligible.
a) Determine the electrical power per unit length of the cylinders (W/m) that is required to maintain the outer surface of cylinder B at 5°C.
b) What is the temperature at the center of cylinder A?