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Chapter 12
Radiation Heat Transfer
0
.
0
67
.
0
08
.
0
16
.
0
16
.
0
112
.
0
075
.
0
037
.
0
=
ε
Δ
⎪
⎭
⎪
⎬
⎫
=
+
=
+
=
+
=
+
c
w
w
w
c
P
P
P
L
P
L
P
Then the effective emissivity of the combustion gases becomes
0.117
0
.
0
062
.
0
1
055
.
0
1
atm
1
,
atm
1
,
=
−
×
+
×
=
ε
Δ
−
ε
+
ε
=
ε
w
w
c
c
g
C
C
Note that the pressure correction factor is 1 for both gases since the total pressure is 1 atm. For a source
temperature of
T
s
= 105
°
C = 378 K, the absorptivity of the gas is again determined using the emissivity
charts as follows:
atm
ft
0.036
atm
m
0109
.
0
K
790
K
378
m)
5
atm)(0.142
16
.
0
(
atm
ft
0.018
atm
m
00545
.
0
K
790
K
378
m)
5
atm)(0.142
08
.
0
(
⋅
=
⋅
=
=
⋅
=
⋅
=
=
g
s
w
g
s
c
T
T
L
P
T
T
L
P
The emissivities of CO
2
and H
2
O corresponding to these values at a temperature of
T
s
= 378 K and 1atm
are, from Fig. 1236,
and
037
.
0
atm
1
,
=
ε
c
062
.
0
atm
1
,
=
ε
w
Then the absorptivities of CO
2
and H
2
O become
0864
.
0
)
062
.
0
(
K
378
K
790
)
1
(
0597
.
0
)
037
.
0
(
K
378
K
790
)
1
(
45
.
0
atm
1
,
45
.
0
65
.
0
atm
1
,
65
.
0
=
⎟
⎠
⎞
⎜
⎝
⎛
=
ε
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
α
=
⎟
⎠
⎞
⎜
⎝
⎛
=
ε
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
α
w
s
g
w
w
c
s
g
c
c
T
T
C
T
T
C
Also
Δα
=
Δε
, but the emissivity correction factor is to be evaluated from Fig. 1238 at
T = T
s
=
378 K
instead of
T
g
=
790 K. We use the chart for 400 K. At
P
w
/(
P
w
+
P
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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, Heat, Radiation

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