Two 3-m-long and 0.4-cm-thick cast iron (k = 52 W/m·K) steam pipes of outer diameter 10 cm are connected to each other through two 1-cm-thick flanges of outer diameter 20 cm. The steam flows inside the pipe at an average temperature of 200°C with a heat transfer coefficient of 180 W/m²·K. The outer surface of the pipe is exposed to an ambient at 12°C, with a heat transfer coefficient of 25 W/m²·K. 

(a) Disregarding the flanges, determine the average outer surface temperature of the pipe.

(b) Using this temperature for the base of the flange and treating the flanges as the fins, determine the fin efficiency and the rate of heat transfer from the flanges.

(c) What length of pipe is the flange section equivalent to for heat transfer purposes?

Transcribed Image Text:

-10 cm +9.2 cm- Tair = 12°C T1cm I1 cm -20 cm- Steam 200°C V