22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Comparison of bulk temperatures under different packing conditions in a
dielectric barrier discharge reactor
S. Jo, D.H. Lee and Y.-H. Song
Korea Institute of Machinery and Materials, 156, Gajeongbuk-ro, Yuseong-gu, KR-305-343 Daejeon, South Korea
Abstract: The heat released from plasma in different packing conditions was compared by
measuring thermal images of a DBD reactor. A typical DBD reactor with a cylindrical
configuration was used, and three different packing conditions were considered: empty,
Al 2 O 3 bead, and crushed Al 2 O 3 . It is found experimentally that the bulk temperature
depends on the discharge power, not the packing conditions. This result may improve the
analysis of the interaction between plasma and catalysis.
Keywords: plasma, dielectric barrier discharge, catalysis, methane, conversion
1. Introduction
Recently, the combination of plasma with catalysis has
attracted considerable attention from researchers who
wish to take advantage of both the high reactivity induced
by the plasma and the high selectivity driven by the
catalyst. Plasma catalysis has been studied for decades as
a potential tool for achieving a breakthrough in existing
catalyst-based chemistry [1]. However, despite the
pioneering work of these researchers, the mechanism of
the plasma catalysis is still not clear. The synergetic
effect of plasma catalysis is due in part to electron impact
reactions and in part to thermal activation by discharge;
however, the relative contributions from each of these
phenomena under specific reaction conditions is not fully
understood. In this study, the effect of possible thermal
activation by discharge was investigated. In packed bed
type plasma catalysis reactions, it is already known that
different packing conditions results in different degrees of
activation [2]. However, it is not clear whether different
packing
conditions
produce
different
thermal
environments that can in turn potentially affect the degree
of activation. In this paper we considered three different
packing conditions and employed a thermal imaging
technique to compare the bulk thermal activation under
these different conditions.
2. Experimental Setup
As shown in Fig. 1, the experimental setup consisted of
a dielectric barrier discharge (DBD) reactor, a power
supply, and an electrical data measurement system. The
DBD reactor had a cylindrical configuration with a
discharge gap of 3.0 mm. The reactant was prepared by
mixing 10 vol% methane with an argon (Ar) gas balance,
and the total flow rate was fixed at 300 cm3/min. Three
different packing conditions were considered: empty,
packing with γ-Al 2 O 3 beads of 1 mm diameter, and
packing with crushed γ-Al 2 O 3 with mesh sizes of 30 - 40,
corresponding to diameters of 0.4 - 0.6 mm. A thermal
image camera with a resolution of 160 × 120 was used to
measure the bulk temperatures of the DBD reactor for
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different packing conditions. All experiments were
carried out using a 10 kHz sinusoidal power supply with
an applied voltage which varied from 4.0 to 6.0 kV. The
discharge power was estimated from an analysis of the
Lissajous figure method.
Fig. 1. Experimental setup for measurement of the heat
released from the plasma of the DBD reactor under
different packing conditions.
3. Result
The bulk temperatures for different packing conditions
were measured at 5 min and 10 min after the discharges
were generated, and the results at a voltage of 6 kV are
shown in Figs. 2 and 3. As time goes on, for each
condition the maximum temperature increases, reaching
almost steady values 10 min after discharge generation. It
is interesting to note that the bulk temperature does not
appear to be affected by the packing conditions. The
experiments were repeated by varying the applied
voltages from 4.0 kV to 6.0 kV; the result is shown in
Fig. 4. Regardless of the packing conditions, the bulk
temperature shows a linear relationship with the discharge
1
power. From this dependence of the bulk temperature on
the discharge power, we can conclude that the total heat
released from plasma depends on the discharge power,
not the packing condition.
of a hot spot arising inside a DBD reactor from the
packing material should be further investigated; such
efforts
could
Fig. 4. Maximum temperatures measured at 5 and 10 min
after discharge ignition for three different packing
conditions.
provide a better understanding of the interaction between
plasma and the packing materials and how to use a
plasma-catalyst hybrid system effectively.
Fig. 2. Discharge images at an applied voltage of 6 kV
for different packing conditions: empty, Al 2 O 3 bead of
1 mm diameter, and crushed Al 2 O 3 with mesh sizes of
30 - 40.
4. Conclusion
In summary, we investigated bulk temperatures inside a
DBD reactor for different packing conditions. As a result,
the total heat released from plasma does not appear to be
affected by the packing conditions, but instead depends
on the discharge power. This result could help with
future analyses of the interaction between plasma and
catalysis.
5. References
[1] T. Nozaki and K. Okazaki. "Non-thermal plasma
catalysis of methane: Principle, energy efficiency,
and applications". Catal. Today, 211, 29 (2013)
[2] S. Jo, D.H. Lee, W.S. Kang and Y.-H. Song.
"Effect of packing material on methane activation in
a dielectric barrier discharge reactor".
Phys.
Plasmas, 20, 123507 (2013)
Fig. 3. Bulk temperatures at the given conditions were
measured with a thermal image camera at 5 and 10 min
after discharge ignition.
Although the total heat released from plasma is
independent of the packing conditions, the local heat
distribution could not be verified in this experiment due to
insufficient image resolution. Therefore, the possibility
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