Chapter 7, Problem 7.137P

It has been suggested that heat transfer from a surface can be augmented by wetting it with water. As a specific example, consider a horizontal tube that is exposed to a transverse stream of dry air. You may assume that the tube, which is maintained at a temperature $T_s>T_{\infty },$ is completely wetted on the outside with a thin film of water. Derive an equation to determine the extent of heat transfer enhancement due to wetting. Evaluate the enhancement for $V=10\text{m/s,}D=10\text{mm,}{T}_s=320\text{K,}$ and $T_{\infty }=300\text{K}\text{.}$