Environmental Engineering Reference
In-Depth Information
Ta b l e 4 . 1
Parameters of the excitation of a
weakly ionized gas in an external electric field.
Here
(rot), and electronic (elec) degrees of free-
dom; the specific released energy
N
e
N
a
)
is expressed in units of 10
29
Wcm
3
,andthe
specific temperature variation (1/
P
/(
N
a
is the number density of gas atoms
or molecules, 1 Td
D
1
10
17
Vcm
2
,
η
is
the energy fraction as a percentage that goes
into elastic (elas), vibrational (vib), rotational
N
e
)(
dT
/
dt
)
isgiveninunitsof10
7
Kcm
3
/s.
ε
,eV
E
/
N
,Td
w
e
,10
6
cm/s
P
N
e
N
Gas
(1/
N
e
)(
dT
/
dt
)
η
elec
η
vib
η
rot
η
elec
He
1
1.2
0.53
100
-
-
-
0.1
0.3
3
3.6
0.94
100
-
-
-
0.54
1.6
Ar
1
0.2
0.2
100
-
-
-
0.006
0.02
3
1.4
0.35
100
-
-
-
0.08
0.23
H
2
1
15
2.4
16
79
5
-
5.8
12
3
60
7
6
93
1
-
67
140
N
2
1
4
0.93
8
83
9
-
0.
1.2
3
105
11
0.2
53
0.5
46
180
380
CO
1
17
3.1
0.7
98
1
-
8.4
17
3
130
13
0.1
54
0.1
46
270
560
CO
2
1
2.4
7
0.1
85
15
-
2.7
4.3
3
60
13
0.1
97
0.1
3
120
200
in the first stage of gas heating, where
c
p
is the heat capacity per molecule at con-
stant pressure. Table 4.1 also contains the pathways of energy consumption;
is
the energy fraction transformed to the corresponding degree of freedom and ex-
pressed as a percentage. In the first stage of this process in molecular gases, the
energy is transformed primarily to vibrational excitation. This is a property em-
ployed in gas discharge of molecular lasers that generate radiation by vibrational-
rotational transitions of molecules.
To provide high efficiency for this method of energy input, we compare it with
heating of a gas through the walls of an enclosure containing this gas. Assuming
that heat transfer occurs by thermal conductivity, we have the estimate
η
T
l
for the heat flux, where
Δ
q
T
is the differ-
ence between temperatures for the walls of the enclosure, and
l
is a dimension of
the enclosure. From this it follows that the specific power introduced by heating
the walls of the enclosure is
is the thermal conductivity coefficient,
Δ
Δ
T
l
2
P
.
10
3
W/(cm K) (a value
corresponding to the thermal conductivity coefficient of air at
T
For a numerical estimate we take
Δ
T
1000 K,
1000 K), and
1W/cm
3
. Such a specific power is reached at atmo-
spheric pressure and a number density of electrons of
N
e
l
1cm. The result is
P
10
9
cm
3
.Becausethe
