22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Development of plasma-liquid system with a secondary discharge and increased
service life
D.K. Gamazin, V.V. Iukhymenko and V.Ya. Chernyak
Taras Shevchenko National University of Kyiv, Kiev, Ukraine
Faculty of Radiophysics, Electronics and Computer Systems, Kiev, Ukraine
Abstract: This paper presents the concept of system, which uses the effects of secondary
discharge on fluids to conduct plasma-chemical processes in liquid medium. Usage of
secondary discharge can increase process selectivity and create specific conditions at the
plasma-liquid boundary. In addition, a method was proposed for increasing system lifetime.
Keywords: Plasma chemistry, selectivity, secondary discharge.
1. Introduction
Today, the issues of energy efficiency and environment
preservation are among the most urgent for humanity.
Traditional manufacturing techniques often use energy
irrationally, and have destructive influence on the
ecological state of our planet. Plasma chemistry is one of
the promising directions that could change this situation.
Its range of applications is very wide - the synthesis of
materials with special properties, energy industry,
creation of new materials, cleaning and disinfection of
water, food and air.
However, this technology, like any other, is not without
its drawbacks. The first of these is the high cost of
electricity. This imposes high demands on the energy
efficiency of such systems. For example, for the problem
of pollutant degradation in [1], the traditional approach
makes it possible to achieve the energy input of about
500-1000 eV/molecule, and for the fuel reformer
problems calorimetric ratio reaches a few tens [2]. A
plasma-catalysis may be the solution to this problem. In
this mode, plasma is used not as a medium for chemical
reactions but as a source of active particles [3]. One of the
results of such approach is the achievement of
calorimetric coefficients of up to 450 during the
reforming of biofuels [4]. Another example is plasmaliquid systems. In this case, separation boundary between
the plasma and the liquid is a source of active species,
which are introduced into the water and trigger chemical
reactions.
On the other hand, the self-consistency of plasma
systems prevents effective management of the processes
in plasma. Even large, by several times, increase of the
discharge current often does not lead to a noticeable
change in the parameters of plasma particles. Possible
solution to this problem is to use a secondary discharge.
This allows to separate the source of charged particles
from the field that accelerates them, which in turn allows
to manage their parameters. The main advantage of this
solution is the ability to manage the potential jump, which
is formed on the surface of liquid. Due to this, the energy
of particles that fall into the liquid can be managed in a
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wide range. This approach improves the efficiency of the
processes of degradation of organic pollutants in water
and water disinfection [5].
Finally, among the most crucial factors is the lifetime of
plasma generator. First of all, it has an important
economic aspect. Frequent failure of equipment leads to
interruptions and reduced efficiency. In addition, the
products of erosion of plasma generator may contaminate
the final products, reducing its quality and increasing
damage to the environment. For this reasons, the creation
of plasma-chemical systems with a long lifetime is a
vitally important task. The examples of such systems are
the devices based on rotating gliding discharge (RGD).
Low thermal load on the electrodes and the distribution of
heat flux over a large area, as well as their simplicity, turn
them into a good choice for the role of plasma generators
with long lifetime
Thus, the development of plasma-chemical systems that
use secondary discharge in plasma-liquid system as a
source of active particles for the problem of plasmacatalysis is an urgent task. RGD has all the necessary
properties to become the primary ionization source in
such systems.
2. Experimental setup
The system designed for this research includes a plasma
generator based on rotating gliding arc and a container for
liquid. Treated medium is exposed to the plasma of
secondary discharge that burns between the main arc and
the liquid surface. Diagram of the apparatus is shown in
Fig. 1.
The plasma generator comprises of a central electrode
1, an upper flange 2, an insulating vortex chamber 3 and a
lower flange 4. The arc of primary discharge 5 burns
between the central electrode and the lower flange.
Secondary discharge 6, which is directly involved in the
processing, burns between primary discharge channel and
the surface of liquid 7. Potential is applied to a liquid by
using a bottom electrode 8, built-in into a bottom flange 9,
which is isolated from the rest of the system by dielectric
inserts 10. The system is fastened with pins 11. Quartz
1
tube 12 performs the role of the container with liquid and
of the chamber for secondary discharge. Diaphragm 13
was designed to create the gap for an exhaust air.
and widens toward the exit. In this conditions, the air
flows of up to 45 liters per minute do not cause strong
instability of liquid surface. In addition, work was carried
out with streams in the range of 10-15 liters per minute. It
provides effective transportation of the plasma of primary
discharge into the area where secondary discharge burns.
C urrent - v oltag e c harac teris tic of s elfdis c harg e
2500
2000
U, V
1500
1000
500
Fig. 1. The experimental setup.
Orifice diameter is selected to be larger than the
diameter of outlet opening in the bottom flange. The main
problem that surfaced in this design is the interaction of
air flow with the free surface of liquid. Resulting
instabilities and irregularities that appeared on the surface
lead to an unstable discharge and increased the risk of
short circuit.
By changing the parameters of the bottom flange outlet
this problem was taken care of. It was established that
hydrodynamic parameters of the system are improved by
decreasing the outlet diameter.
0
0
0,05
Fig. 2.
discharge
2
I, A
0,15
U V, (Q=20) averag e
0,2
0,25
U V, (Q=30) averag e
Current-voltage characteristic of primary
The ignition of secondary discharge between the bottom
flange and bottom electrode was done via application of
voltage. Ignition was observed at the voltage of 4,5-5 kV.
Discharge appearance is shown on Fig. 3.
Plasma
of RGD
3. Results of experiment
The objectives of initial experiment included:
•
Investigation of the electric parameters of
discharge.
•
Selection of the optimal design in terms of
interaction between airflow and liquid surface.
•
Obtaining stable burning mode for secondary
discharge.
Current-voltage characteristic of primary discharge is
shown on Fig. 2.
Characteristic shows monotonic decrease with the
increase of current. This CVC behaviour is typical for
devices with the self-setting arc length. This tells us that
discharge plays an important role in the shunting of arc.
Due to this phenomenon the area of contact between
discharge and electrodes increases, which may extend
device lifetime. The disadvantages of this mode are strong
ripple current and voltage, which create additional risk to
power supply, as well as generate noise in a wide range of
radio frequencies. System can interfere with electrical
devices.
During experiments, it was found out that the optimal
design is one with the 6 mm diameter of bottom flange
outlet. Furthermore, the output channel has conical shape
0,1
U V, (Q=10), averag e
"Liquid" electrode
of secondary discharge
Liquid
Fig. 3. Pulse is not an independent discharge
Secondary discharge is represented by pulses that
briefly appear between the arcs of primary discharge and
liquid surface. Averaged current of secondary discharge is
60-100mA.
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4. Conclusions
System, presented in this paper, allows us to study the
impact of secondary discharge on fluid. After some
design improvements aimed at increase of the discharge
stability and the expansion of the range of operating
voltages it will be possible to study the impact of
discharge on various environments.
Secondary discharge allows to control the energy of
particles that are introduced into liquid.
The system can be used for plasma chemical water
purification and disinfection.
5. Acknowledgements
This work was partially supported by Taras Shevchenko
National University of Kyiv, National Academy of
Sciences of Ukraine, Ministry of Education and Science
of Ukraine.
6. References
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[2] Nishiyama H. et al. Decomposition of Acetic Acid
Using Multiple Bubble Jets with Pulsed Electrical
Discharge //Plasma Chemistry and Plasma Processing.
March 2015, Volume 35, Issue 2, pp 339-354.
[3] V.Ya. Chernyak, O.A. Nedybaliuk, E.V. Martysh,
V.V. Iukhymenko,
I.V. Prysiazhnevych,
Ol.V. Solomenko, Iu.P. Veremii. Plasma catalysis of
chemical reactions // Problems of Atomic Science and
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– P. 124-129.
[4] І.І. Федірчик, О.А. Недибалюк, В.Я. Черняк
Плазмово-каталітичне реформування біопалив // XXII
щорічна
наукова
конференція
І-ту
ядерних
досліджень НАН України, Тези доповідей, 26-30 січня
2015р., Київ, Україна.-2015.-С.153-154.
[5] Tarasova Ya., Chekhovskaya T., Gruzina T.,
Chernyak V., Yukhymenko V., Babich I.. Active
decontamination system for neutralization of dangerous
micro-organisms in water// Abstr. The Second World
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