Chemistry Reference
In-Depth Information
This method combines the chemical conversions in nonthermal plasma chemical
reactors directly to important operation parameters (e.g., the power input, flow
rate,
) by means of macroscopic determined rate coefficients
k
i
in the compe-
tent reaction equations. By this, the method allows a very compact description of
different plasma chemical reactors. For a long time the macroscopic kinetics was a
pure phenomenological method, far away from first principles [7-9].
As a first step, the power input
P
of the reactor acts as the fundamental discharge
parameter. Neglecting in a crude approximation the explicit influence of all other
species
n
1
,
n
2
,
...
...
on the source term except that of the considered species
n
i
, one
gets:
S
i
=
S
i
(
P
,
n
i
)
[9]. With the ad hoc ansatz
G
i
=
k
Gi
·
P
and
L
i
=
k
Li
n
i
·
P
the integration of the PFM (4.3) results in the so-called kinetic curve
exp
−
exp
−
,
n
i
(
)
n
i
∞
z
k
Li
zP
v
0
k
Li
A
·
z
·
τ
0
P
=
1
−
=
1
−
(4.13)
V
A
where
n
i
∞
=
k
Gi
/
k
Li
is the “equilibrium concentration” at
P
→∞
A
is cross section of the AZ.
The rate coefficients
k
i
must be determined experimentally as functions of the reactor
operating conditions, for example, the gas pressure
p
. Kinetic curves have proved up
to now their suitability for several chemical processes. But they are not a universal
mean at all. Only in special cases the so-called specific energy τ
0
P
/
V
A
(see (4.13))
is a true similarity parameter which determines
n
i
only in the shown combinations.
Therefore, a more general base of MAK named generalized MAK has been developed
and validated [1-3,6]. The starting point is a suitable schematic model of the non-
thermal plasma chemical reactor. Within this concept the AZ and PZ of the reactor
are represented as black boxes with input and output flows of only stable chemical
components and with an effective source term for each of these species, representing
a mean value. The reactor model adequate to this physical situation is the BMM,
discussed previously. Further details can be found in Refs. [1-3]. In particular, it has
been shown that chemical quasi-equilibrium states are especially important for this
method. These states represent a characteristic phenomenon of the overall behavior
of gas discharge reactors and reflects the basic role of gross reactions even for
nonthermal plasma chemical conversions, see Section 4.3.
4.5 PLASMA CHEMICAL SIMILARITY
4.5.1 I
NTRODUCTION
The formulation and application of similarity principles starts with the foundation
of modern physics. Today, many physical and process engineering disciplines make
use of very efficient similarity methods and scaling laws. On the other hand plasma
