A standard 10-cm steel pipe (ID = 10.066 cm, OD = 11.25 cm) carries superheated steam at 6508C in an enclosed space where a fire hazard exists, limiting the outer surface temperature to 38ºC. To minimize the insulation cost, two materials are to be used: first a high-temperature (relatively expensive) insulation is to be applied to the pipe, and then magnesia (a less expensive material) will be applied on the outside. The maximum temperature of the magnesia is to be 315ºC. The following constants  are known:

(a) Specify the thickness for each insulating material.
(b) Calculate the overall heat transfer coefficient based on the pipe OD. 

(c) What fraction of the total resistance is due to (1) steam-side resistance, (2) steel pipe resistance, (3) insulation (the combination of the two), and (4) outside resistance? 

(d) How much heat is transferred per hour per meter length of pipe?

Transcribed Image Text:

steam-side coefficient high-temperature insulation conductivity magnesia conductivity outside heat transfer coefficient steel conductivity ambient temperature h = 500 W/(m²K) k = 0.1 W/(mK) k = 0.076 W/(mK) h = 11 W/(m²K) k = 43 W/(mK) 21°C Ta