22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Innovative powder transportation using dielectric barrier discharge tube
H. Takana1, S. Nakakawaji2, S. Uehara1 and H. Nishiyama1
1
2
Institute of Fluid Science, Tohoku University, Sendai, Japan
Formerly. Graduate School of Engineering, Tohoku University, Japan
Abstract: “DBD Tube” has been proposed for nano particle transportation with particle
surface purification in this study. Nano particles in the DBD tube can be transported in
axial direction with swirl. Particles near the electrode wall jump around due to electric
static force, which can suppress particle clogging in the tube. The characteristics of plasma
induced internal flow in a tube have been experimental clarified in this study. Furthermore,
the effects of electrode angle, and electric operating conditions on the DBD tube
characteristics were investigated to clarify the optimum operating conditions as well as the
configuration of “DBD Tube”.
Keywords: DBD, particle transportation, plasma actuator, electrostatic mixing
1. Introduction
The particulate matter contained in the exhaust gas
from automobile and factories has been gaining attentions
as an emerging environmental problem. Furthermore, in a
material processing, the choking of the powder transfer
tube often occurs for ultra fine powders of several tens of
nano meter due to agglomeration of powders on the tube
wall. The efficient transportation of ultra fine powders is
strongly required.
The authors have developed the dielectric barrier
discharge tube (hereafter referred to as “DBD tube”) as an
innovative technology for ultra fine powder transfer [1].
Our developed plasma tube has a dielectric barrier surface
discharge (DBD) structure on its inner surface.
In this study, the fundamental characteristics of the
DBD tube were quantitatively clarified, such as discharge
characteristics, plasma induced flow field visualized by
stereo-PIV measurement. The effects of electrode angels
and operating conditions on the induced flow
characteristics has been clarified.
Fig. 1. Cross-sectional view of DBD tube.
Fig. 2. Schematics of experimental setup.
2. Experimental Setup and Measurement Systems
Figure 1 shows the cross-sectional view of the
developed plasma tube. The inner diameter of the plasma
tube is 20 mm and the tube is made of
polytetrafluoroethylene (PTFE) as dielectrics. The
thickness and length of the tube are 0.3 mm and 100 mm,
respectively. Two cupper electrodes with 5 mm width are
spirally wrapped both on the inner and outer surfaces of
the tube with interval of 3 mm and 4 mm alternately. The
dielectric barrier discharge is generated on the inner
surface of the tube between exposed and immersed
electrodes along.
Figure 2 shows schematic illustration of experimental
setup. The sinusoidal voltage signal from function
generator (NF Corporation, WF1973) is amplified to 1317 kVpp by high voltage amplifier (Matsusada Precision
Inc., HAP-10B10). The voltage frequencies are set to
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500, 1000 and 1500 Hz. Three dimensional induced
velocity fields were measured by stereo-PIV method[2]
at 2 to 3 mm downstream from tube exit. For the stereo
PIV measurement, oil mist of average diameter of 1 to 10
micro meter is seeded to the flow as a tracer.
3. Results and Discussion
Figure 3 (a) and (b) show the photos of luminescence in
a DBD tube and powder transportation for applied voltage
of 14.6 V pp at 1 kHz, respectively. The powder is alumina
with average diameter of 30 nm. The discharge is quite
uniform along 3 mm electrode gap between a pair of
spiral electrode. The powder placed inside the tube is
successfully transported to axial direction just by plasma
induced internal flow [3]. Particles on the edge of
the exposed electrode jump around by electrostatic force.
1
Swirl ratio
2.0
(a)
1.0
0
0
1.0
tan(90o-θ)
2.0
0 kV pp
14.6 kV pp
(b)
Fig. 3. Photos of (a) discharge luminescence in a DBD
tube and (b) powder transportation by a DBD tube.
Induced flow rate (L/min)
Fig. 5. Swirl ratio of induced flow for electrode angle.
10
8
θ = 60o
500 Hz
1000 Hz
1500 Hz
6
4
2
0
0
1
1.5
0.5
Power (W)
Fig. 6 Induced flow rate as a function of
discharge power.
Fig. 4. Velocity vectors obtained from stereo-PIV at
2 mm downstream from the exit of “DBD tube” for
electrode angle of 60o at 500 Hz.
Figure 4(a)-(c) show 3 dimensional averaged flow
velocity vectors along with axial flow velocity
distribution at 2 mm downstream from the tube exit for
14.3 – 16.7 kV at 1.5 kHz using tube with electrode angle
of 35o. The discharge induced flow is a swirling flow with
axial and azimuthal component and very small radial
component. The flow is induced only in the vicinity of
inside tube wall and its axial velocity is approximately 50
cm/s. It is clearly shown from these figures that induced
flow is accelerated with applied voltages and higher swirl
is obtained.
Figure 5 shows the dependence of electrode angle on
swirling ratio of the induced flow. The swirling ratio is
defined as the ratio of azimuthal velocity to the axial
velocity. The swirling ratio is almost the same as the
value of tan(90o-θ), which means that the flow is induced
perpendicular to the electrode. This result shows that the
swirling ratio can be controlled by electrode angel.
Because the residence time of particles is decided by
swirling ratio, electrode angle should be large for
increasing particle transportation rate, or should be small
for increasing particle residence time for particle surface
2
treatment by discharge generated radicals and ozone.
Figure 6 shows induced flow rate measured by stereoPIV for discharge power at 2 mm downstream from the
tube exit. The induced flow rate increases almost linearly
with discharge power. For the electrode angle of 60o,
higher flow rate can be obtained at lower frequency even
under the same discharge power. The maximum flow rate
was 7.5 l/min in this experiment.
4. Conclusions
An innovative “DBD tube” has been developed for high
efficiency nano powder transportation with surface
treatment. It has been clarified from stereo-PIV that the
swirling flow is induced by DBD and the swirling ratio
and powder residence time can be controlled by electrode
angle. Induced flow rate linearly increases with discharge
power.
References
[1] H. Takana, K. Shinohara and H. Nishiyama,
Japanese Patent, 2010-242718
[2] C. Shekhar, K. Nishino, Y. Yamane and J. Huang, J.
of Visualization, 15, pp. 293-308 (2012)
[3] J. P. Boeuf, Y. Lagmich, TH. Challlegari, L. C.
Pitchford, AIAA Paper 2007-183 (2007)
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