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Chapter 12
Radiation Heat Transfer
Chapter 12
RADIATION HEAT TRANSFER
View Factors
121C
The view factor
represents the fraction of the radiation leaving surface i that strikes surface j
directly. The view factor from a surface to itself is nonzero for concave surfaces.
F
ij
→
122C
The pair of view factors
and
are related to each other by the reciprocity rule
where A
i
is the area of the surface i and A
j
is the area of the surface j. Therefore,
F
→
F
ji
→
AF
A F
ii
j
j j
i
=
F
A
A
F
1 12
2
21
12
2
1
21
=⎯
→
⎯=
123C
The summation rule for an enclosure and is expressed as
where N is the number of
surfaces of the enclosure. It states that the sum of the view factors from surface i of an enclosure to all
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 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat, Radiation

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