Athin electrical heater is wrapped around the outer surface of a long cylindrical tube whose inner surface is maintained at a temperature of 5°c. the tube wall has inner and outer radii of 25 and 75 mm, respectively, and a thermal conductivity of 10 w/m·k. the thermal contact resistance between the heater and the outer surface of the tube (per unit length of the tube) is 0.01 m·k/w. the outer surface of the heater is exposed to a fluid with t=-10 deg c and h=100 w/m^2*k. the surrounding temp is assumed to be 47 deg c. what is the heater power per unit length of tube required to maintain the heater at t=25 deg c?