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Heat Transfer
book

Heat Transfer

by Younes Shabany
December 2009
Intermediate to advanced content levelIntermediate to advanced
523 pages
18h 30m
English
CRC Press
Content preview from Heat Transfer
Radiation Heat Transfer 329
The spectral-directional absorptivity is dened as the fraction of the spectral
intensity at wavelength λ incident in the direction of θ and ϕ,
I
iλ
λθφ
,
(,,)
, that is
absorbed by the surface,
αλθφ
λθφ
λθφ
λθ
λ
λ
,
,
,
(,,)
(,,)
(,,)
.=
I
I
a
i
(13.31)
The relationships between the spectral-directional absorptivity, spectral absorp-
tivity, and total absorptivity are
αλ
αλθφ λθφθθθφ
λ
λθ λ
θ
()
(,,) (,,)cossin
,,
=
=
Idd
i
0
ππ
φ
π
λ
θ
π
φ
λθφθθθφ
/
,
/
(,,)cossin
2
0
2
0
2
∫∫
=
==
Idd
i
00
2π
,
(13.32)
α
αλ λλ
λλ
=
() ()
.
Gd
G
0
(13.33)
Equations 13.29 through 13.31 shows that the surface absorptivity of an object is
independent from its own temperature. Howev ...
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Publisher Resources

ISBN: 9781439814680