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Chapter 15
Steady Heat Conduction
370
A 50m 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 onedimensional 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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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat

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