Chapter 3
Steady Heat Conduction
(
b
) The thickness of the insulation needed that would maintain the outer surface of the insulation at a
maximum temperature of 40°C can be determined from
C/W
02274
.
0
C
)
20
40
(
C/W
02274
.
0
0.23876
)
12
.
0
/
ln(
03079
.
0
C
)
20
235
(
3
3
3
insulation
o,
2
2
insulation
total,
2
1
insulation
°
°
−
=
°
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
+
°
−
→
−
=
−
=
∞
∞
∞
D
D
D
R
T
T
R
T
T
Q
&
whose solution is
cm
2.22
=
=
=
⎯→
⎯
=
2
12

16.44
2

thickness
m
1644
.
0
2
3
3
D
D
D
3173
A 6mdiameter spherical tank filled with liquefied natural gas (LNG) at 160°C is exposed to
ambient air. The time for the LNG temperature to rise to 150°C is to be determined.
Assumptions
1
Heat transfer can be considered to be steady since the specified thermal conditions at the
boundaries do not change with time significantly.
2
Heat transfer is onedimensional since there is thermal
symmetry about the midpoint.
3
Radiation is accounted for in the combined heat transfer coefficient.
3
The
combined heat transfer coefficient is constant and uniform over the entire surface.
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat, Heat Transfer, RO

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