Chemistry Reference
In-Depth Information
the operating parameters of the reactor. This is possible via (4.26). Introducing the
pressure
p
=
nkT
, one obtains
ε
τ
0
P
pV
A
2
3
τ
e
n
δ
kT
e
0
U
e
τ
0
n
e
=
and ε
=
.
(4.29)
Obviously, the main similarity quantity τ
0
n
e
is determined by a new basic
dimensionless reactor parameter
R
, which contains the former specific energy
τ
0
P
pV
A
=
τ
0
P
W
N
kT
g
,
/
R
=
V
A
nkT
g
)
=
(4.30)
(
where
W
is the input of energy
N
the number of particles
Regarding the physical meaning of this parameter, one sees:
R
represents the energy invested per particle of the gas mixture during the
flow through the active reactor zone in relation to the thermal energy
kT
g
.
The factor of proportionality ε in (4.29) is a true constant for constant gas and
electron temperature. Of course, to guarantee corresponding values of
T
g
and
U
e
,
extra conditions must be fulfilled, as already mentioned. But under some restrictions
of the operation of nonisothermal plasma chemical reactor variations of
T
g
and
U
e
remain small and ε
const is a tolerable approximation. The most important of
these restrictions are sufficient high gas pressure and sufficient low Joule heating of
the gas. The latter means nearly constant reduced field strength
E
≈
/
n
and
U
e
(or
T
e
),
respectively.
At small
R
→
0 the reduced summed effective source terms are proportional
to
R
, (i.e., τ
0
S
i
/
n
∼
R
), for created species with τ
0
n
e
∼
R
. Large
R
→∞
results
in τ
0
S
i
/
const. and then the quasi-equilibrium states are reached and can be
interpretedastheresultofanelectronicallymodifiedmassactionlaw,whichdescribes
a complex chemical situation by a reversible gross reaction.
n
→
4.5.5 E
XPERIMENTAL
P
ROOF
To prove in a systematic manner the applicability of the dimensionless reactor param-
eter
R
, the separate variations of all the four quantities which are of influence should
be analyzed with regard to changes of the output values
x
i
=
n
at equal input.
According to the analysis given, only such plasmas should be included, which show
nearly equal gas and electron temperatures. The energy distribution function of elec-
trons, neglecting Coulomb interaction, is mainly determined by the reduced electric
field strength
E
n
i
/
n
. Therefore we have to look on such plasma conditions which do
not differ too much in
E
/
/
n
.
