Civil Engineering Reference
In-Depth Information
Fig. 8.3
Heat transfer through a multilayer pipe
8.3.2 Cylindrical Surface Multilayer System (See Fig.
8.3
)
This example is typical of pipelines for steam or other hot fluids. The same
approach can also be followed in the case of cold fluids.
The flow of heat is:
t
i
t
o
Q
¼
A
R
th
where
A
Lr
i
) surface of the pipeline of length
L
. Note that the
R
th
expression will be modified by the choice between the outside
and the inside surface,
r
i
¼
¼
the outside (2
π
Lr
o
) or the inside (2
π
inside pipe radius,
r
o
¼
outside multilayer pipe radius.
Thus:
outside surface
(m
2
)
(ft
2
)
A
¼
2
π
L
r
o
(outside surface)
X
n
r
o
r
i
þ
1
j
r
o
ln
r
j
þ
1
1
h
i
1
h
o
m
2
C
ft
2
F
R
th
¼
k
j
r
j
þ
=
W
h
=
Btu
inside surface
(m
2
)
(ft
2
)
A
¼
2
π
L
r
i
(inside surface)
X
n
1
j
r
i
ln
r
j
þ
1
r
i
r
o
1
h
i
þ
1
h
o
m
2
C
ft
2
F
R
th
¼
k
j
r
j
þ
=
W
h
=
Btu
