22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Plasma chemical reactor on a base of dielectric barrier discharge for molecules
dissociation
V. Malanichev, V. Khomich, M. Malashin and S. Moshkunov
Institute for Electrophysics and Electric Power RAS, Saint Petersburg, Russia
Abstract: Plasma chemical reactor (PCR) was designed to study chemical reactions in the
dielectric barrier discharge (DBD) plasma. Electron energy distribution functions (EEDFs)
were calculated to determine the number of electrons with required energy for dissociation
of water molecules by electron strike in the DBD plasma.
Keywords: Dielectric Barrier Discharge, water, Boltzmann equation
1. Introduction
PCR was designed to study chemical reactions in the
DBD plasma [1]. The method of estimating the
parameters of PCR to implement the selected reaction is
considered by the example of a water molecule. We
considered EEDFs assuming one electron strike for
dissociation of water molecules. Numerical calculations
were carried out by website lxcat.net.
2. Experimental setup
PCR operates at atmospheric pressure. Reduced electric
field in discharge gap was between 160 and 260 Td. More
detailed information of the geometrical configuration of
PCR, power supply and diagnosis system are given in
previous articles [1-5].
Table 1. Dissociation processes
Process
number
Process expression
1
e + H2O → e + H-+ OH (7 eV), excitation
2
e + H2O → e + O + H2 (13 eV), excitation
3
e + H2O → H- + OH, attachment
4
e + H2O → H2 + O-, attachment
5
e + H2O → OH- + H, attachment
Process 1 has highest reaction rate value. The
probability of this process will have a higher value than
others if electron energy range is between 13 and 23 eV
(except elastic collisions) (Fig. 2) [7].
3. Theoretical calculation
Calculation of reaction rates for the dissociation of
water molecules by electron strike is introduced in Fig. 1
[6]. The calculation was carried out for the operation
range of reduced electric field between 160 and 260 Td.
Considered processes are listed in Table 1.
Fig. 2. e/H 2 O collision cross sections; + – elastic
collisions; o – process 1; * – excitation without
dissociation; x – ionization; triangle – process 2;
Fig. 1. Variation of reaction rates as a function of E/N; x –
process 1; o – process 2; * – process 3; + – process 4;
triangle – process 5.
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EEDFs were calculated to determine the number of
electrons with required energy. EEDFs were calculated
for reduced electric field between 160 and 260 Td. EEDFs
for two boundary cases are presented in Fig. 3 [6]. The
range from 13 to 23 eV was marked by two vertical lines.
As can be seen from the graphs, this range lies in the
beginning of the downturn EEDFs. Further sharp decrease
1
in the value EEDFs can be explained by the fact that the
electrons actively lose energy in the process of ionization
and dissociation of water molecules.
Pressure Low Temperature Plasma Chemistry (HAKONE
XIV), pp. 27-31
[5] E. Shershunova, M. Malashin, S. Moshkunov, V.
Khomich. Generation of Homogeneous Dielectric Barrier
Discharge in Atmospheric Air without Preionization.
Abstract Book. 19th International Vacuum Congress.T11
Plasma Science and Technology. PST–P2-02. Paris. 2013.
P.1242.
[6] G. J. M. Hagelaar and L. C. Pitchford, "Solving the
Boltzmann equation to obtain electron transport
coefficients and rate coefficients for fluid models",
Plasma Sci Sources and Tech 14, 722 (2005).
[7] Morgan database, www.lxcat.net, retrieved on
February 25, 2015.
Fig. 3. EEDFs; solid line – 160 Td; dashed line – 260 Td.
4. Conclusion
According to theoretical estimations of collision cross
sections we can conclude that the dissociation of water
molecules in the plasma by electron strike will be the
most effective if the energy of electrons is from 13 to 23
eV. EEDFs were calculated to determine the number of
electrons in this range under the conditions realized in the
developed PCR. Thus the applied voltage to the PCR
electrodes from 10 to 16 kV corresponds to optimum
theoretically calculated regime of operation for
dissociation of water molecule by one electron strike.
5. References
[1] Malanichev V. E., Malashin M. V., Moshkunov S. I.
Khomich V. Yu. Reactor based on DBD for plasma
chemical reaction carring out Book of Contributions, VII
International Symposium on Theoretical and Applied
Plasma Chemistry./ ISCTU – Ivanovo, 2014. – 472 p.
pp. 428-430
[2] Khomich, V. Yu., Malashin, M. V., Moshkunov, S. I.,
Rebrov, I. E., Shershunova, E. A. High voltage IGBT
switch with capability of pulse width control Abstract
Book SPEEDAM 2012 - 21st International Symposium on
Power Electronics, Electrical Drives, Automation and
Motion
PP.
1512
–
1514
doi:
10.1109/SPEEDAM.2012.6264541
[3] V. Yu. Khomich, M. V. Malashin, S. I. Moshkunov,
E. A. Shershunova, V. A. Yamschikov Series Circuit
Resistance as Factor of DBD Mode in Air at Different
Barrier Materials IEEE Transactions on Plasma Science,
2014, Vol. 42, Issue 10, pp. 3314-3320 (DOI:
10.1109/TPS.2014.2347704)
[4] Vladislav Khomich, Victor Malanichev, Maxim
Malashin, Sergey Moshkunov, Ekaterina Shershunova
“Forming and study of volume diffuse DBD in
atmospheric air without preionisation”. Book of
Contributions of 14th International Symposium on High
2
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