Chapter 3, Problem 3.48P

A thin electrical heater is wrapped around the outer surfaceof a long cylindrical tube whose inner surface ismaintained at a temperature of $5°\text{C}\text{.}$ The tube wall hasinner and outer radii of 25 and 75 mm, respectively, anda thermal conductivity of $\text{10}\text{W/m}\cdot \text{K}\text{.}$ The thermal contactresistance between the heater and the outer surfaceof the tube (per unit length of the tube) is $R_{t,c}^{\text{'}}=0.01\text{m}\cdot \text{K/W}\text{.}$ The outer surface of the heater is exposedto a fluid with $T_{\infty }=-10°\text{C}$ and a convection coefficientof $h=100{\text{W/m}}^2\cdot \text{K}\text{.}$ Determine the heater powerper unit length of tube required to maintain the heater at $T_o=25°\text{C}\text{.}$