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International Journal of Plasma Environmental Science and Technology Vol.2, No.1, MARCH 2008
26
The effect of a strip-type third electrode of a wire-plate type nonthermal
plasma reactor on corona discharge and ozone generation characteristics
1
J. Moon1, J. Jung1, and S. Gum2
Graduate School of Electrical Engineering & Computer Science, Kyungpook National University, Daegu, Korea
2
School of Electronic Engineering, Kumoh National Institute of Technology, Gumi, Korea
Abstract—The effect of a strip-type third electrode of a wire-plate type nonthermal plasma reactor on discharge and
ozone generation characteristics has been investigated. When the third electrode, a thin aluminum strip, is installed near
the corona wire, a significantly increased corona onset voltage, and the amount of output ozone and the ozone yield, can be
obtained. The effect of biased voltages of the strip-type third electrode has also been investigated. These, however, reveal
that the strip-type third electrode could concentrate the electric flux to the upper side on the corona wire, thus enhancing
the activity of corona discharge, with a reduction in consumption of the corona power of the plasma reactor. As a result,
higher amounts of the output ozone, and the ozone yield, for positive and negative corona discharges, respectively, can be
obtained. This proves the effectiveness of the third electrode.
Keywords— third electrode, wire-plate type, nonthermal plasma, ozone generation, corona discharge
I. INTRODUCTION
The nonthermal plasma technique offers an
innovative approach to the effective removal of pollutant
gases [1-3]. The effective removal of pollutant gases,
however, requires the generation of an intense discharge
in the processing region of the plasma reactor [4-6]. The
removal of pollutant gases can be stimulated by a
discharge-induced electrophysicochemical reaction [2, 4,
6-10]. This electrophysical reaction originates from
energetic electrons [6-8], while the electrochemical
reaction is mainly caused by the ozone that is produced
from the corona discharge [2, 4, 9-10]. There are several
types of plasma reactors, utilizing a corona discharge [4,
10], an arc discharge [11-12], and an electron beam [7].
An arc discharge and an electron beam type of plasma
reactors use mainly the electrophysical reaction to treat
the gases [6, 11, 12]. This type of plasma reactor
generates little ozone. A plasma reactor utilizing a corona
discharge uses mainly the chemical reaction of ozone to
react with pollutant gases [2, 4, 9-13]. This type of
plasma reactor needs to generate a large amount of ozone.
And for this type of plasma reactor, the effective
generation of ozone is a key technology in applying the
nonthermal plasma practically and efficiently in the
treatment of pollutant gases [2, 4, 9-10].
A corona discharge from the wire-plate type
nonthermal plasma reactor is now used as a means for
removing pollutant gases [8-10]. This is because of its
wider gas processing space and its simple structure. Due
to the low density of the discharge plasma, a small
amount of ozone can be produced and allowed to react
with a pollutant gas. As a result, the overall removal
efficiency of the wire-plate type nonthermal plasma
reactor is not sufficient in applying in the treatment of
Corresponding author: Jae-Duk Moon
e-mail address: [email protected]
Received; September 20, 2007, Accepted; December 12, 2007
pollutant gases [6, 14].
When a third electrode is set near the corona wire of
a conventional wire-plate type nonthermal plasma reactor,
it would repel the electric flux line toward the opposite
side of the corona wire surface [14-17]. This repelling
action of the third electrode, however, would increase the
electric flux density on the opposite side of the corona
wire. As a result, an intensive corona discharge on the
corona wire could be obtained. This repelling action
could be controlled by varying the dimensions of the
strip of the third electrode and the bias voltages applied
to the third electrode.
In this paper, a wire-plate type nonthermal plasma
reactor, with a strip-type third electrode, has been
proposed and investigated by focusing on the discharges
and the generation of ozone. Corona discharges and the
ozone generation characteristics of the proposed wireplate type nonthermal plasma reactor have been
investigated, with and without a third electrode, by
varying the dimensions of the strip-type third electrode
and the bias voltages of the third electrode. The results
were analyzed and compared.
II. EXPERIMENTAL SETUP
A schematic diagram of the experimental setup is
shown in Fig. 1. The setup consists of a proposed wireplate type nonthermal plasma reactor (WPR) with a striptype third electrode (STE), a high-voltage DC power
supply circuit, an AC/DC bias voltage, an oxygen gas
feeder, an ozone monitor, and current and voltage
measurement sets, as shown in Fig. 1.
An adjustable DC high voltage was applied between
the corona wire electrode and the plate electrode. The
bias voltage of the STE, DC, AC voltage or ground, was
selected by a rotary switch. The AC bias voltage was
fixed at 4kVpp magnitude, and the frequency was varied
between 60Hz and 3 kHz.
Moon et al.
27
TP
GO
TW
PE
CW
s
h
GI
PR: nonthermal plasma reactor
OM: ozone monitor
DCHV: DC high voltage
RP : protection resistor
SA: surge arrestor
HP: HV probe with DVM
OG: oxygen gas feeder
CC : charging capacitor
RM: measurement resistor
SO: storage oscilloscope
SW: rotary switch
BV : bias voltage
Fig. 1. Schematic of the experimental setup.
TE
w
TT
CW: corona wire
PE: plate electrode
TE: strip-type third electrode
TP: plate electrode terminal
TW: corona wire terminal
TT: third electrode terminal
GI: gas inlet
GO: gas outlet
w : width of strip
s : wire-plate gap spacing
h : height of strip-type third electrode from corona wire
Fig. 2. Configuration of the proposed WPR with an STE.
The applied voltage and current were measured using
a digital voltmeter (Fluke, 75) and a HV probe (1,000:1,
Tektronix, P6015A), and a measurement resistor (metal
film type) with a surge arrestor, as shown in Fig. 1. The
corona current waveform was observed by a storage
oscilloscope (Tektronix, TDS 340A) at the measurement
resistor. The ozone concentration from the gas outlet of
the proposed WPR was measured using an ozone monitor
(Dasibi DY 1500). Oxygen gas (99.6% pure), from a gas
bottle, was fed into the gas inlet of the proposed WPR at
a constant flow rate of 1.0 ℓpm.
Fig. 2 shows a closeup of the configuration of the
proposed WPR with the STE. A wire (stainless steel,
0.18mm in diameter and 80mm in length) and a plate
(stainless steel, 0.6mm thick and 80mm in diameter)
were used to form the corona wire and the plate electrode,
respectively. For the STE, an aluminum strip (0.01mm
thick and 80mm in length), was glued to an insulator disk
(mica sheet, 0.5mm thick and 80mm in diameter), and
placed under the corona wire electrode. The width (w) of
the strip of the STE was set between 1.5 and 5.0mm. The
height (h) of the STE from the corona wire was set
between 1.5 and 10.0mm. The wire-plate gap spacing (s)
was fixed at 10.0mm.
III. EXPERIMENTAL RESULTS AND DISCUSSION
A. The effect of the grounded strip-type third electrode
Fig. 3 shows the positive and negative I-V
characteristics of the proposed WPR, with and without
the STE, for the different h and w of the STE. The
positive and negative corona currents, ICs, without the
STE, slowly increased from their corona onset voltage,
VCs, for the positive and negative coronas, as the applied
HV increased. Then, the ICs gradually increased and
broke down as the applied HV increased for the positive
and negative coronas, respectively. With the STE, the
positive and negative I-V characteristics significantly
differed from those without the STE. The ICs rapidly
increased from their elevated corona onset voltage, VCs,
as the applied high voltage increased. The ICs reached
somewhat lower peaks as compared with those without
the STE.
Fig. 4 shows the positive and negative VC and VB
characteristics of the proposed WPR, with and without
the STE, respectively, as a function of the height of the
STE. There were significant increases in the VCs along
with decreases in height for both the positive and
negative corona discharges, respectively. The increased
VCs were about 9.1~16.7kV and 9.6~16.8kV, which are
about 1.23~2.26 and 1.25~2.18 times higher than those
without the STE, for the positive and negative corona
discharges, respectively, as shown in Fig. 4 (a). The VBs
also changed by about 14.1~16.7kV and 16.2~18.2kV,
which are about 0.99~1.18 and 0.94~1.06 times those
without the STE, for the positive and negative corona
discharges, respectively. The VBs, however, decreased to
those of the VBs without the STE, along with an increase
in height, for both the positive and negative corona
discharges, respectively, as shown in Fig. 4 (b).
The reason for these changes of the corona discharge
characteristics, such as the corona currents, the onset
voltages, and the breakdown voltages, as shown in Figs.
3 and 4, can be explained as follows. When an STE with
the same potential as that of the corona wire of the wireplate gap is installed in the vicinity of the corona wire,
there would be two actions, the corona-wire-diameter
enlarging action and the flux-line repelling action. The
corona-wire-diameter enlarging action appears when an
STE is installed closely to the corona wire, the STE acts
as a part of the corona wire. As a result, the apparent
diameter of the corona wire is increased. While the fluxline repelling action originates from the STE having the
same potential as the corona wire, then the STE repels
the flux lines of the lower side to the upper side of the
surface of the corona wire, at its configuration as shown
International Journal of Plasma Environmental Science and Technology Vol.2, No.1, MARCH 2008
28
1.0
h=1.5mm
h=3.0mm
h=5.0mm
h=7.5mm
h=10.0mm
without 3rd E(w=0)
0.8
0.6
Corona Current, IC [mA]
Corona Current, IC [mA]
1.0
∗∗
∗
∗
positive corona
0.4
s=10.0mm
w=3.0mm
0.2 breakdown :∗
∗
∗
0.0
6
8
10
12
14
16
0.8
0.6
0.4
0.2
∗
∗
0.0
18
20
6
8
Applied DC Voltage, VDC [kV]
(a)
∗∗
∗∗
h=1.5mm
h=3.0mm
h=5.0mm
h=7.5mm
h=10.0mm
without 3rd E(w=0)
negative corona
s=10.0mm
w=3.0mm
breakdown :∗
10
12
14
16
18
20
Applied DC Voltage, V DC [kV]
positive corona (w=3.0mm)
(b) negative corona (w=3.0mm)
25
N C : negative corona
PC : positive corona
Breakdown Voltage, VB [kV]
Corona Onset Voltage, VC [kV]
Fig. 3. I-V characteristics of the proposed WPR for different width and height of the STE.
w =1.5m m , N C
w =1.5m m , PC
w =3.0m m , N C
w =3.0m m , PC
w =5.0m m , N C
w =5.0m m , PC
w ithout 3rd E , N C
w ithout 3rd E , PC
20
15
10
5
0
2
4
6
8
10
20
15
5
N C : negative corona
PC : positive corona
0
12
0
2
H eight of T hird E lectrode, h [m m ]
h=1.5m m , N C
h=1.5m m , PC
h=3.0m m , N C
h=3.0m m , PC
h=5.0m m , N C
h=5.0m m , PC
h=7.5m m , N C
h=7.5m m , PC
h=10.0m m , NC
h=10.0m m , PC
w ithout 3rd E, N C
w ithout 3rd E, PC
16
14
12
10
8
6
0
2
4
6
8
10
W idth of Third Electrode, w [m m ]
(a)
Breakdown Voltage, VB [kV]
Corona Onset Voltage, VC [kV]
N C : negative corona
PC: positive corona
18
4
6
8
10
12
H eight of T hird E lectrode, h [m m ]
(b) breakdown voltage, VB
corona onset voltage, VC,
Fig. 4. VC and VB of the proposed WPR as a function of the height of the STE.
(a)
20
w =1.5m m , N C
w =1.5m m , PC
w =3.0m m , N C
w =3.0m m , PC
w =5.0m m , N C
w =5.0m m , PC
w ithout 3rd E, N C
w ithout 3rd E, PC
10
20
N C: negative corona
PC: positive corona
19
h=1.5m m , N C
h=1.5m m , PC
h=3.0m m , N C
h=3.0m m , PC
h=5.0m m , N C
h=5.0m m , PC
h=7.5m m , N C
h=7.5m m , PC
h=10.0m m , N C
h=10.0m m , PC
w ithout 3rd E, N C
w ithout 3rd E, PC
18
17
16
15
14
13
0
2
4
6
8
10
W idth of Third Electrode, w [m m ]
corona onset voltage, VC
(b) breakdown voltage, VB
Fig. 5. VC and VB of the proposed WPR as a function of the width of the STE.
in Fig. 2. As a result, the flux lines are concentrated
toward the upper surface of the corona wire, and
concurrently, the flux density on the upper surface of the
corona wire increases. Total flux lines of the corona wire
surface, however, would be reduced, compared to those
without the STE.
These actions, the corona-wire-diameter enlarging
action and the flux-line repelling action, would be
influenced by the height of the strip of the STE and the
width of the STE [14, 17]. Smaller height and wider
width enlarge the apparent diameter of the corona wire
and repel and concentrate more electric flux lines toward
the upper side of the corona wire. As a result, the corona
discharge characteristics, such as the corona currents, the
onset voltages, and the breakdown voltages, would be
changed, as shown in Figs. 3, and 4.
Fig. 5 shows the positive and negative VC and VB
characteristics of the proposed WPR, with and without
the STE, as a function of the width of the STE. The VC
increased in width between 1.5 and 5.0mm for both the
positive and negative corona discharges. The VBs was
determined as being in mostly the same amounts as those
Moon et al.
29
h=1.5m m
h=3.0m m
h=5.0m m
h=7.5m m
h=10.0m m
w ithout 3rd E(w =0)
1400
1200
1000
800
400
∗∗
∗
∗
∗
positive corona
s=10.0m m
w =3.0m m
breakdow n :∗
600
1600
Ozone Output, O3 [ppm]
Ozone Output, O3 [ppm]
1600
200
∗
0
6
8
10
12
14
16
h=1.5mm
h=3.0mm
h=5.0mm
h=7.5mm
h=10.0mm
without 3rd E(w=0)
1400
1200
1000
800
∗ ∗∗
∗∗
negative corona
s=10.0mm
w=3.0mm
breakdown :∗
600
400
200
0
18
20
6
A pplied D C V oltage, V D C [kV ]
8
10
12
14
16
18
20
Applied DC Voltage, V DC [kV]
Peak Ozone Output, O3P [ppm]
Peak Ozone Output, O3P [ppm]
(a) positive corona (w=3.0mm)
(b) negative corona (w=3.0mm)
Fig. 6. Ozone generation characteristics of the proposed WPR for different width and height of the STE.
1600
1400
1200
1000
800
600
w =1.5m m
w =3.0m m
w =5.0m m
w ithout 3rd E
400
200
positive corona
0
0
2
4
6
8
10
1600
1400
1200
1000
800
600
w =1.5m m
w =3.0m m
w =5.0m m
w ithout 3rd E
400
200
negative corona
0
0
12
2
4
6
8
10
12
Peak Ozone Output, O3P [ppm]
Peak Ozone Output, O3P [ppm]
H eight of Third Electrode, h [m m ]
H eight of T hird E lectrode, h [m m ]
(a) positive corona case
(b) negative corona case
Fig. 7. The peak ozone output of the proposed WPR as a function of the height of the STE.
1600
1400
1200
1000
800
h=1.5mm
h=3.0mm
h=5.0mm
h=7.5mm
h=10.0mm
without 3rd E
600
400
200
positive corona
0
0
1
2
3
4
5
6
Third Electrode Width , w [mm]
(a)
1600
1400
1200
1000
800
h=1.5mm
h=3.0mm
h=5.0mm
h=7.5mm
h=10.0mm
without 3rd E
600
400
200
negative corona
0
0
1
2
3
4
5
6
Width of Third Electrode, w [mm]
positive corona case
(b) negative corona case
Fig. 8. The peak ozone output of the WPR as a function of the width of the STE.
without the STE, but fluctuated along with the increase in
width for both the positive and negative corona
discharges. These increases and decreases in the VC and
VB with variations of the width would have been caused
by an effect of the STE. As shown in Fig. 5, there is an
optimum condition of the width of the STE. The VCs and
VBs increased with an increase in the width, until the
width is 3mm, this would be due to the corona-wirediameter enlarging action of the STE, as shown in left
sides of Fig. 5 (a) and (b). But when the width increases
further, due to the enhanced flux-line repelling action, the
corona discharging surface on the corona wire becomes
reduced onto the top surface of the wire, which decreases
the VCs and VBs, as shown in right sides of Fig. 5 (a) and
(b).
Fig. 6 shows the ozone generation characteristics of
the proposed WPR. These characteristics were obtained
just before VBs, with and without the STE and for the
different height and width of the STE. The ozone outputs
were initiated at the VCs, and they increased with an
increase in the applied HV until the peak ozone outputs
were reached near the VBs. Their peak ozone outputs
increased significantly, compared with those without the
STE, for the positive and negative corona discharges.
Figs. 7 and 8 show the peak ozone outputs (O3Ps), as
a function of the height and width of the STE, for the
positive and negative corona discharges of the proposed
International Journal of Plasma Environmental Science and Technology Vol.2, No.1, MARCH 2008
30
TABLE 1
SPECIFIC DATA COMPARISONS OF THE PROPOSED WPR WITH AND WITHOUT THE GROUNDED STE.
Discharge Polarity &
Plasma Reactor Types
Positive
Corona
Negative
Corona
WPR without STE
w=1.5
WPR
with
w=3.0
STE
w=5.0
WPR without STE
w=1.5
WPR
with
w=3.0
STE
w=5.0
VB
[kV]
ICP
[mA]
PP
[W]
PP
Comparison [-]
O3P
[ppm]
14.2
14.3
14.4
14.2
17.2
17.6
18.0
17.3
0.47
0.16
0.19
0.21
0.80
0.70
0.68
0.69
6.67
2.29
2.74
3.00
13.76
12.32
12.24
11.94
1.00
0.34
0.41
0.45
1.00
0.90
0.90
0.87
650
862
940
932
1,100
1,201
1,252
1,245
WPR, respectively. The peak ozone outputs increased
significantly as compared with those without the STE,
for the positive and negative corona discharges. The peak
ozone outputs, about 1,220ppm and 1,304ppm, for the
positive and negative corona discharges, respectively,
were obtained near 10.0mm in height and 3.0mm in
width, these are about 1.88 and 1.19 times higher than
those obtained without the STE.
These results would be due to the flux-line repelling
action of the STE, that intensifies the corona discharge as
shown in Fig. 3, as a result, the ozone generation would
also be enhanced at the optimum condition of the width
and height, as shown in Figs. 7 and 8.
Table 1 shows specific data comparisons of the
proposed WPR, with and without the STE, for different
width and a constant height of 3.0mm of the STE. The
peak corona currents (ICPs) of the proposed WPR, with
the STE, those were obtained just before the VBs, were
weaker than those without the flux repelling action of the
STE. As a result, the corona power consumption
(PP=ICPVB) reduced 0.34~0.90 times, compared with
those without the STE, for the positive and negative
corona, respectively, as shown in Table 1. In addition,
the yields of the output ozone (Y=O3MP/PP) increased
significantly, more than 3.12~3.84 times and 1.17~1.25
times, compared with those without the STE, for the
positive and negative corona respectively. The peak
ozone outputs of 940ppm and 1,252ppm, for the positive
and negative corona discharges, show increases of about
1.45 times and 1.14 times, compared to those of 650ppm
and 1,100ppm, respectively, without the STE. These
increases, however, would be due to the effect of the STE.
From these results, the proposed WPR with an STE
could concentrate the electric flux density, thus
enhancing the activity of the corona discharges on the
corona wire, producing more ozone with reduced corona
power consumption. The proposed WPR, with an STE,
may be useful as an effective corona discharge and ozone
generator that can remove pollutant gases efficiently.
B. The effect of the biased strip-type third electrode
In order to investigate the effect of the bias voltage
applied to the STE on the corona discharge and ozone
generation characteristics of the proposed WPR, 4
experimental set points on the positive and negative
curves of the ozone generation characteristics, were
determined. The set points A, B, C and D indicate the
O3P
Y
Comparison [-] [g/kWh]
1.00
1.33
1.45
1.43
1.00
1.09
1.14
1.13
12.63
48.44
44.17
39.43
10.71
12.53
13.09
13.41
Y
Comparison
[-]
1.00
3.84
3.50
3.12
1.00
1.17
1.22
1.25
ozone output points of 98, 90, 80 and 50% of the peak
ozone output, respectively.
Fig. 9 shows the effect of the positive and negative
DC bias voltage of the STE, (Vb), on the corona current
of the proposed WPR. A bias voltage that has an opposite
polarity between the STE and a corona wire electrode
would be able to increase the flux lines on a corona wire
and concurrently intensify the corona discharge on a
corona wire. At the same time, more ions would be
generated due to the intensified corona discharge and
increased corona current, as shown on the left side of Fig.
9 (a) and the right side of Fig. 9 (b). The bias voltage,
which has the same polarity between an STE and a
corona wire electrode, forms a less flux line on the
corona wire and weakens the corona discharges. As a
result, fewer corona currents are generated, as shown on
the right side of Fig. 9 (a) and the left side of Fig. 9 (b).
Fig. 10 shows the effect of the DC bias voltage of the
STE on the ozone output of the proposed WPR. The
increased flux lines, due to the repelling action of the
STE, produce more output ozone. This is well in
correlation with the negative corona case, as shown in
Fig. 10 (b). Regarding the positive corona case, however,
the ozone output increased when the corona current
decreased, as shown in Fig. 10 (a).
A negative corona discharge shows many spot-like
discharges on a corona wire [18-20]. The spot-like
discharges of the negative corona discharge are hard to
propagate laterally on a corona wire. In addition, the
negative corona intensity is in proportion to the corona
current from the spot-like discharge on a corona wire. A
higher corona current produces more output ozone for the
negative corona [14]. As a result, the output ozone
increased 1.11 times (1,413ppm), for Vb=7kV at the set
point of A, than that of the output ozone (1,278ppm) of
the no-biased (grounded) STE, as shown in Fig. 10 (b).
For the positive corona, however, there are no spotlike discharges on the positive corona wire [19-20]
because the positive coronas are easy to propagate
laterally and to concentrate partially on a corona wire.
These concentrated corona discharges on the positive
corona wire mainly control the positive corona current
generation.
In this experiment for the positive corona of the
proposed WPR with the higher-DC-voltage-biased STE,
the repelling action becomes stronger than that of the nobiased (grounded) STE. The flux lines are concentrated
on the upper surface of the corona wire, and,
Moon et al.
31
(a) positive corona discharge case
(b) negative corona discharge case
Fig. 9. The effect of the DC bias voltage of the STE on the corona current.
(a)
positive corona discharge case
(b) negative corona discharge case
Fig. 10. The effect of the DC bias voltage of the STE on the ozone output.
VDC=14 kV
VDC=13kV
Vb=4kVpp, f=100Hz
Vb= 4kVpp, f=100Hz
Fig. 11. The effect of the AC bias voltage of the STE on the corona current waveforms.
(Upper: applied DC voltage, Middle: corona current, Bottom: AC bias voltage)
concurrently, the corona discharges intensified
significantly. These intensified positive corona
discharges can propagate to the partial points on the
upper surface of the corona wire and transfer from the
normal glow corona toward the higher-current-andthermal abnormal glow corona mode [17-19]. The
production rate of ozone in the mode of the abnormal
corona discharge decreases significantly caused by the
decomposition of the produced ozone, due to the vast
heat generated on the reduced corona surface, in the
ozone production region [21-22]. As a result, a stronger
corona current is generated but produces less ozone [2122]. This would be the reason why the ozone output
decreased in the higher-current positive corona case, as
shown on the right side of Fig. 10 (a).
Fig. 11 shows the waveforms of the corona current
that were measured across the measurement resistor at
the set point D when the AC bias voltage (the AC bias
voltage (Vb) of 4kVpp and the biased AC frequency (f) of
100Hz) was applied. As shown in Fig 11, the corona
discharges on the corona wires occur only at the opposite
polarity of the applied half cycle of the AC bias voltage,
International Journal of Plasma Environmental Science and Technology Vol.2, No.1, MARCH 2008
Output Ozone , O3 [ppm]
32
h=10.0mm
800 s=10.0mm
w=3.0mm
600
400
negative corona with grounded 3rd E
positive corona with grounded 3rd E
negative corona with AC bias voltage
positive corona with AC bias voltage
200
0
0
1000
2000
3000
Frequency of Bias Voltage, f [Hz]
Fig. 12. The effect of AC bias voltage of the STE on the ozone
output.
and no discharge is shown at the same polarity of the half
cycle of the AC bias voltage [23]. These switching
characteristics of the corona current, shown by applying
the AC bias voltage of the STE of the proposed WPR,
appeared between the point just before the VC and near
the VB, at the biased AC frequency (f) between 60Hz and
3kHz. Since the corona discharges on the corona wire
occurred only during the half cycle of the biased AC
frequency, the amounts of output ozone and corona
currents decreased to about half values of those of the nobiased (grounded) ones.
Fig. 12 shows the effect of the biased AC frequency
(f) on the ozone generation characteristics. When the
biased AC frequency increases, the amount of output
ozone increases, and the output ozone exceeds that of the
no-biased grounded ones, as much as a peak value of 1.1
times for f≥1.5kHz and 1.9 times at f=3kHz in the
positive corona, respectively. For the negative corona,
there is a little increase in ozone output. These increased
amounts of the output ozone, however, would be caused
by the increased corona power and the intensified corona
discharge due to the elevated biased AC frequency.
These results show that the controlling and switching
of the corona discharge and the ozone output could be
realized by varying the biased voltage and frequency of
the STE of the proposed WPR.
IV. CONCLUSION
A wire-plate type nonthermal plasma reactor, with a
strip-type third electrode installed in the vicinity of the
corona electrode, has been investigated by focusing on
the generation of ozone and corona discharge of the
corona wire electrode. The following conclusions have
been obtained:
The proposed wire-plate type nonthermal plasma
reactor, with a strip-type third electrode which repels the
electric flux lines toward the upper side of the corona
wire, generated intense corona discharges on the upper
surface corona wire. As a result, the proposed wire-plate
type nonthermal plasma reactor, with the strip-type third
electrode, could produce more ozone, about 940 and
1,252ppm, compared to those amounts of 650 and
1,100ppm without the third electrode, which are about
1.45 and 1.14 times higher for the positive and negative
discharges, respectively.
This flux repelling action, however, reduced the
total flux lines on the corona wire surface and the corona
power consumption. This reduction of the corona power
consumption increased the yields of the output ozone
significantly, by 3.12~3.84 and 1.17~1.25 times for the
positive and negative corona discharges, respectively,
compared with those of without the third electrode. In
addition, by varying the bias voltage and frequency, not
only the characteristics of the corona discharge can be
controlled/switched, but also the amount of output ozone
can be controlled/elevated.
This proposed type of wire-plate nonthermal plasma
reactor, with the strip-type third electrode, may be useful
in generating effective corona discharges and in
removing pollutant gases.
ACKNOWLEDGEMENT
This work was supported by the Korea Research
Foundation Grant funded by the Korean Government
(MOEHRD) (KRF-2006-521-D00189). Also we extend
our gratitude to the BK21 Program, Korea.
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