For this problem why would all the heat generated by the heater be absorbed by the air and not by both the inner tube and the
a very thin electrical heater is fitted between a long circular rod and a concentric tube with inner and outer radii of 20 and 40 mm, respectively. the rod (a) has a thermal conductivity of ka = 0.15 w/m⋅k. the tube (b) has a thermal conductivity of kb = 1.5 w/m⋅k and its surface is subjected to convection with a fluid of temperature t∞ = -15°c and heat transfer coefficient 50 w/m2⋅k. there is negligible thermal contact resistance between the cylinder surfaces and the heater. (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, and (b) what is the temperature at the center of cylinder a?