A thin electrical heater is wrapped around the outer surface of a long cylindrical tube whose inner surface is maintained at a temperature of 10C. The tube wall has inner and outer radii of 30 and 80mm, respectively, and a thermal conductivity of 5W/mK. The outer surface of the heater is exposed to a fluid with T=15C and a convection coefficient of h=125W/m2K. Determine the heater power per unit length of tube required to maintain the heater at T0=20C