A 50-m·long section of a steam pipe wl)ose outerdiameter is 10 cm passes through an open space at 15°C. The average temperature of the outer surface of the pipe is measured to be 150°C. If the combined heat transfer coefficient on the outer surface of the pipe is 20 W/nr·K, determine (a) the rate of heat loss from the steam pipe; (b) the annual cost of this energy lost if steam is generated in a natural das fumace that has an efficiency of 75 percent and the price of natural gas is $0.52/therm (1 therm = 105,500 kJ); and (c) the thickness of fiberglass insulation (k - 0.035 W/m·K) needed in order to save 90 percent of the heat lost. Assume the pipe temperature to remain constant at 150°C.
FIGURE P3-75
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