Chapter 15 Steady Heat Conduction 3-70 A 50-m long section of a steam pipe passes through an open space at 15 ° C. The rate of heat loss from the steam pipe, the annual cost of this heat loss, and the thickness of fiberglass insulation needed to save 90 percent of the heat lost are to be determined. Assumptions 1 Heat transfer is steady since there is no indication of any change with time. 2 Heat transfer is one-dimensional since there is thermal symmetry about the center line and no variation in the axial direction. 3 Thermal conductivity is constant. 4 The thermal contact resistance at the interface is negligible. 5 The pipe temperature remains constant at about 150 ° C with or without insulation. 6 The combined heat transfer coefficient on the outer surface remains constant even after the pipe is insulated. Properties The thermal conductivity of fiberglass insulation is given to be k = 0.035 W/m ⋅ °C. Analysis
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