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Chapter 3
Steady Heat Conduction
Review Problems
3152E
Steam is produced in copper tubes by heat transferred from another fluid condensing outside the
tubes at a high temperature. The rate of heat transfer per foot length of the tube when a 0.01 in thick layer
of limestone is formed on the inner surface of the tube is 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 centerline and no variation in the axial
direction.
3
Thermal properties are constant.
4
Heat transfer coefficients are constant and uniform over the
surfaces.
Properties
The thermal conductivities are given to be
k
= 223 Btu/h
⋅
ft
⋅
°F for copper tubes and
k
= 1.7
Btu/h
⋅
ft
⋅
°F for limestone.
Analysis
The total thermal resistance of the new heat exchanger is
&
&
()
.
Q
TT
R
R
Q
new
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat

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