Environmental Engineering Reference
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seen in
Figure 2.112
). In both flames the furnace temperature conditions were very
similar, and it may be inferred that the high values are largely due to wall radiation.
450
400
350
300
250
200
150
100
Coal
Heavy fuel oil
Natural gas
Light fuel oil
50
0
0
1
2
3
Axial Position [m]
4
5
6
FIGURE 2.113
Total radiative heat fluxes for NG, LFO, and HFO flames.
2.5.3.4.8 Total Radiance
Total radiance measurements were performed by traversing the flame with a cold
target sighted by a narrow angle radiometer probe,
60
which remained in a fixed
position at the opposite wall of the furnace (see
Figure 2.114
)
.
To minimize reflections at the target surface, this was blackened using Zynolite
paint with a total normal emissivity of 0.94. The paint was shielded from the hot
combustion gases using an N
2
purge. During the measurements, the cold target
temperature was kept between 25 and 45˚C. Total radiance measurements have been
carried out 205 cm downstream of the burner outlet, and have been compared with
model predictions
(
Figure 2.115
)
.
Total radiance predictions have been performed using the Exponential Wide
Band Model
61
and the Chan and Tien scaling method.
62
This model is formulated
for nonhomogeneous and nongray gas/soot mixtures.
63
The total radiance leaving a
nonscattering media of length
L
is given by the following equation:
(
)
∞
L
∂
τ
sL
s
′
,
"
#
∫
∫
()
′
()
=
() (
)
IL
I
00
τ
,
Ld
ν
+
ν
Isdsd
0
ν
(2.30)
ν
ν
ν
∂ ′
ν
=
0
ν
=
0
where
I
(
L
) is total medium intensity in W/(m
2
sr),
I
v
(0) is the spectral intensity
incident upon the medium,
I
v
0
is the blackbody spectral intensity in W/(m
2
·sr·cm
-1
),
and
v
is the wave number in cm
-1
. τ
v
(
s
′,
L
) is the spectral emissivity of a column of
gas of length (
L
-
s
′), and is defined as:
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