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MECE 4364 Heat Transfer
Prof. Dong Liu
Department of Mechanical Engineering
University of Houston
1
Lecture 5 – Sep 7, 2010
Lecture 5
Conduction
2
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Thermal Circuits: Plane Wall
R
tot
=
1
h
1
A
+
L
kA
+
1
h
2
A
3
,1
,2
total
x
TT
T
R
qq
∞∞
−
Δ
==
14
11
ABC
tot
LLL
R
hA k A k A k A hA
=++ + +
R
tot
=
L
E
k
E
A
+
k
F
A
2
L
F
+
k
G
A
2
L
G
⎡
⎣
⎢
⎤
⎦
⎥
−
1
+
L
H
k
H
A
Lecture 5
Tube Wall
Solution:
Heat flux:
Heat flow:
T
(
r
)
=
T
s
−
T
s
,2
ln
r
1
r
2
()
ln
r
r
s
⎛
⎝
⎜
⎞
⎠
⎟
+
T
s
,2
′
′
q
r
=−
k
dT
dr
=
kT
s
−
T
s
,2
(
)
r
ln
r
2
r
1
q
r
kA
dT
dr
=
2
π
rL
′
′
q
r
=
2
Lk T
s
−
T
s
,2
ln
r
2
r
1
4
Conduction thermal resistance: (
compare to plane wall
)
Overall thermal resistance:
(
dependence on r
1
and r
2
?
)
Lecture 5
Composite Tube Wall
()
,1
,4
,4
21
32
43
11
4 4
ln
ln
ln
22
2
2
2
r
tot
ABC
TT
q
rr
R
hr
L
k
L
k
L
k
L
L
ππ
π
∞∞
−
−
==
++++
(
)
44
ln
ln
1
2
ln
1
tot
AB
C
R
L
k
L
k
L
kL
h
rL
=+
+
++
5
,4
,4
r
tot
qU
A
T
T
R
−
−
Define the overall heat transfer coefficient
Lecture 5
Spherical Shell
Solution:
Heat Flux:
Heat Flow:
T
(
r
)
=
T
s
−
T
s
−
T
s
,2
1
−
r
1
r
(
)
1
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This note was uploaded on 01/27/2011 for the course MECE 4364 taught by Professor Lipinglui during the Winter '10 term at University of Houston.
 Winter '10
 LipingLui

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