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PROBLEM 4.10
K
NOWN:
Temperature, diameter and burial depth of an insulated pipe.
F
IND:
Heat loss per unit length of pipe.
SCHEMATIC:
ASSUMPTIONS:
(1) Steadystate conditions, (2) Onedimensional conduction through
insulation, twodimensional through soil, (3) Constant properties, (4) Negligible oil
onvection and pipe wall conduction resistances.
c
PROPERTIES:
Table A3
, Soil (300K):
k = 0.52 W/m
⋅
K;
Table A3
, Cellular glass (365K):
= 0.069 W/m
⋅
K.
k
A
NALYSIS:
The heat rate can be expressed as
12
tot
TT
q
R
−
=
w
here the thermal resistance is R
tot
= R
ins
+ R
soil
.
From Equation 3.28,
()
( )
21
ins
ins
n D / D
n 0.7m/0.5m
0.776m K/W
R.
2 Lk
2 L 0.069 W/m K
L
ππ
⋅
==
=
×⋅
AA
F
rom Equation 4.21 and Table 4.1,
1
1
2
soil
soil
soil
cosh
2z/D
cosh
3/ 0.7
1
0.653
Rm
Sk
2
0.52 W/m K L
L
=
=
⋅
K
/
W
.
H
ence,
120 0
C
W
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This note was uploaded on 12/07/2010 for the course MAE Heat Trans taught by Professor Lee,j.s. during the Spring '10 term at Seoul National.
 Spring '10
 LEE,J.S.
 Heat Transfer, Insulation

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