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Chapter 11
Fundamentals of Thermal Radiation
1131
A surface is subjected to radiation emitted by another surface. The solid angle subtended and the rate
at which emitted radiation is received are to be determined.
Assumptions
1
Surface
A
1
emits diffusely as a blackbody.
2
Both
A
1
and
A
2
can be approximated as
differential surfaces since both are very small compared to the square of the distance between them.
Analysis
Approximating both
A
1
and
A
2
as differential
surfaces, the solid angle subtended by
A
2
when viewed from
A
1
can be determined from Eq. 1112 to be
A
1
= 4 cm
2
T
1
= 600 K
θ
2
= 60
°
r
= 80 cm
1
= 45
°
A
2
= 4 cm
2
sr
10
3.125
4
−
−
×
=
°
=
θ
=
≅
ω
2
2
2
2
2
2
2
,
1
2
cm)
80
(
60
cos
)
cm
4
(
cos
r
A
r
A
n
since the normal of
A
2
makes 60
°
with the direction of viewing.
Note that solid angle subtended by
A
2
would be maximum if
A
2
were positioned normal to the direction of viewing. Also, the
point of viewing on
A
1
is taken to be a point in the middle, but
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Radiation

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