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Chapter 15
Steady Heat Conduction
355
A wall is constructed of two layers of sheetrock spaced by 5 cm
×
12 cm wood studs. The space
between the studs is filled with fiberglass insulation. The thermal resistance of the wall and the rate of heat
transfer through the wall are to be determined.
Assumptions
1
Heat transfer is steady since there is no indication of change with time.
2
Heat transfer
through the wall is onedimensional.
3
Thermal conductivities are constant.
4
Heat transfer coefficients
account for the radiation heat transfer.
Properties
The thermal conductivities are given to be
k
= 0.17 W/m
⋅
°C for sheetrock,
k
= 0.11 W/m
⋅
°C for
wood studs, and
k
= 0.034 W/m
⋅
°C for fiberglass insulation.
Analysis
(
a
) The representative surface area is
A
=
×
=
10
6
5 0
6
5
..
m
2
. The thermal resistance network and
the individual thermal resistances are
T
∞
1
R
1
R
i
R
2
R
3
R
5
R
4
T
∞
2
W
15
.
5
C/W
858
.
4
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Resistance, Mass, Heat

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