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Chapter 15
Steady Heat Conduction
356E
A wall is to be constructed using solid bricks or identical size bricks with 9 square air
holes. There
is a 0.5 in thick sheetrock layer between two adjacent bricks on all four sides, and on both sides of the wall.
The rates of heat transfer through the wall constructed of solid bricks and of bricks with air holes 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
= 0.40 Btu/h
⋅
ft
⋅
°F for
bricks,
k
= 0.015 Btu/h
⋅
ft
⋅
°F
for air, and
k
= 0.10 Btu/h
⋅
ft
⋅
°F for sheetrock.
Analysis
(
a
) The representative surface area is
. The thermal resistance
network and the individual thermal resistances if the wall is constructed of solid bricks are
A
==
(./ )
.
7 5 12 7 5 12
0 3906 ft
2
F/Btu
h
57
.
308
ft
)]
12
/
5
.
0
(
)
12
/
7
(
F)[
Btu/h.ft.
10
.
0
(
ft
12
/
9
F/Btu
h
288
ft
)]
12
/
5
.
0
(
)
12
/
5
.
7
(
F)[
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat

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