NCSUMAE310
HW08
H
OMEWORK
#8
Provide a clear concise solution for each of the following radiative heat transfer problems.
For
all problems, assume steady heat transfer in a nonparticipating medium.
1.
The “crossedstrings” method of Hottel provides a simple means to calculate view factors
between surfaces that are of infinite extent in one direction.
For two such surfaces (a) with
unobstructed views of one another, the view factor is of the form
F
12
=
1
2 w
1
(a c + b d)  (a d + b c)
Use this method to evaluate the view factors F
12
for sketches (b) and (c).
A
1
A
2
a
b
c
d
w
1
1 m
4 m
A
1
A
2
1 m
4 m
A
1
A
2
(a)
(b)
(c)
2.
Determine the shape factor F
12
for the perpendicular rectangles shown.
0.2 m
0.4 m
0.3 m
0.5 m
1
2
3.
Determine F
12
and F
21
for the following configurations using the reciprocity theorem and
other basic shape factor relations.
Do not use tables or charts.
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NCSUMAE310
HW08
(a)
A
1
A
2
90�
Long duct
(b)
A
1
A
2
Small sphere of area A
1
under a
concentric hemisphere of area A
2
=2A
1
(c)
A
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 Fall '08
 Kuznetsov
 Geometry, Heat Transfer, Pallavolo Modena, Sisley Volley Treviso, diameter

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