Common practice in chemical processing plants is to clad pipeinsulation with a durable, thick aluminum foil. The functions ofthe foil are to confine the batt insulation and to reduce heattransfer by radiation to the surroundings. Because of the presenceof chlorine (at chlorine or seaside plants), the aluminum foilsurface, which is initially bright, becomes etched with in-servicetime. Typically, the emissivity might change from 0.12 atinstallation to 0.36 with extended service. For a 300-mm-diameterfoil-covered pipe whose surface temperature is 90 C, will thisincrease in emissivity due to degradation of the foil finish have asignificant effect on heat loss from the pipe? Consider two caseswith surroundings and ambient air at 25 C: (a) quiescent air and(b) a cross-wind velocity of 10 m/s.
