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Q21. Wet steam at a pressure of 7.0 bar flows in a 5-m long pipe of inside diameter 38 mm and wall thickness 5 mm. The pipe is surrounded with a layer of lagging 15 mm thick. The thermal conductivity of the lagging is 0.05 W/m K and the outside surface heat transfer coefficient is 12 W/m² K. The outside air temperature is 30°C. The thermal resistances of steam film and pipe wall may be disregarded. Determine EACH of the following:

(a) The rate of heat loss; (7)

(b) The outside surface temperature of the lagging; (3)

(c) The increase in the rate of heat loss which would result if the thickness of the lagging were reduced to 10mm