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Chapter 1
Basics of Heat Transfer
113E
A logic chip in a computer dissipates 3 W of power. The amount heat dissipated in 8 h and the heat
flux on the surface of the chip are to be determined.
Assumptions
Heat transfer from the surface is uniform.
Analysis
(
a
) The amount of heat the chip dissipates during an 8hour period is
Logic chip
W
3
=
Q
&
QQ
t
==
=
=
&
()
(
)
Δ
38
2
4
W
h
W
h
0.024 kWh
(
b
) The heat flux on the surface of the chip is
2
W/in
37.5
=
=
=
2
in
08
.
0
W
3
s
s
A
Q
q
&
&
114
The filament of a 150 W incandescent lamp is 5 cm long and has a diameter of 0.5 mm. The heat flux
on the surface of the filament, the heat flux on the surface of the glass bulb, and the annual electricity cost
of the bulb are to be determined.
Assumptions
Heat transfer from the surface of the filament and the bulb of the lamp is uniform .
Analysis
(
a
) The heat transfer surface area and the heat flux on the surface of the filament are
2
cm
785
.
0
)
cm
5
)(
cm
05
.
0
(
=
=
=
ππ
DL
A
s
2
6
W/m
10
1.91
×
=
=
=
=
2
2
W/cm
191
cm
785
.
0
W
150
s
s
A
Q
q
&
&
(
b
) The heat flux on the surface of glass bulb is
2
2
2
cm
1
.
201
cm)
8
(
=
=
=
D
A
s
2
W/m
7500
=
=
=
=
2
2
W/cm
75
.
0
cm
1
.
201
W
150
s
s
A
Q
q
&
&
(
c
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Power, Heat

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