Woo Seok Kang

Numerical study on influences of barrier arrangements on dielectric barrier discharge characteristics

A numerical study has been carried out to understand the influences of barrier arrangements on the discharge characteristics of dielectric barrier discharge (DBD). A 1.5-dimensional (1.5-D) modeling is considered in the arrangements of bare, single-barrier, and double-barrier electrodes while a two-dimensional (2-D) approach is employed in a configuration of ferroelectric packed discharge (FPD). Numerical simulations show that the evolution of microdischarges in DBD occurs sequentially in the three distinctive phases of avalanche, streamer, and decay, and that the dielectric barriers make streamer discharges stabilized and sustained in lowered electric fields without transition to spark compared with no barrier case. Especially, the highly nonuniform strong electric field effect created by the pellets appears to be formed in FPD, which enables the flue gas cleaning to be expected to enhance the decomposition efficiency.

Effect of the Electric Conductivity of a Catalyst on Methane Activation in a Dielectric Barrier Discharge Reactor

The influence of catalyst electric conductivity on methane activation in a planar-type dielectric barrier discharge reactor is investigated by empirically comparing the degree of methane conversion of bare Al2O3 with that of Pt/Al2O3; from this, it is determined that the latter catalyst converts less methane owing to the presence of Pt. Calculations and comparisons of electric fields with and without Pt show that the presence of a Pt catalyst results in a lower electric field than does bare Al2O3. An analysis of product gases based on the correlation between the fragmentation of radicals and the electric field also indicates that the electric field is decreased by using Pt. From these results, it can be concluded that the synergies between the plasma and the conductive catalysts need to be reassessed for different electric field conditions, and that further studies of non-conductive catalysts that can enhance methane activation and synergistic effects are needed.

Methane activation using noble gases in a dielectric barrier discharge reactor

The conversion of methane is measured in a planar-type dielectric barrier discharge reactor using three different noble gases—He, Ne, and Ar—as additives. The empirical results obtained clearly indicate that methane activation is considerably affected by thy type of noble gas used. Through 0-D calculations, the discharge parameters inside the reactor, i.e., electron temperature and electron density, are estimated using experiment results. A comparison of the discharge characteristics and experimental results shows that the electron temperature is an important factor in achieving high methane activation and the mixture with Ar gas shows the highest methane conversion. These results are constructed using the mechanisms of energy and charge transfer from excited and ionized noble gas atoms to methane molecules, considering the number density of active atoms of noble gases. Finally, electron temperatures obtained for gas mixtures having different reactant compositions and concentrations are analyzed to estimate methane activation.

Effect of packing material on methane activation in a dielectric barrier discharge reactor

The conversion of methane is measured in a planar-type dielectric barrier discharge reactor using γ-Al2O3 (sphere), α-Al2O3 (sphere), and γ-Al2O3 (16–20 mesh). Investigations on the surface properties and shape of the three packing materials clearly indicate that methane activation is considerably affected by the material used. Capacitances inside the discharge gap are estimated from charge–voltage plots, and a comparison of the generated and transferred charges for different packing conditions show that the difference in surface properties between γ- and α-phase Al2O3 affects the discharge characteristics. Moreover, all packing conditions show different charge characteristics that are related to the electron density. Finally, the packing materials shape affects the local electron temperature, which is strongly related to methane conversion. The combined results indicate that both microscale and macroscale variations in a packing material affect the discharge characteristics, and a packing material shoul...

Combination of Plasma with a Honeycomb-Structured Catalyst for Automobile Exhaust Treatment

To activate a catalyst efficiently at low temperature by plasma for environmental control, we developed a hybrid reactor that combines plasma with a honeycomb-structured catalyst in a practical manner. The reactor developed generated stable cold plasma at atmospheric pressure because of the dielectric and conductive nature of the honeycomb catalyst by consuming low amounts of power. In this reactor, the applied voltage and temperature determined the balance between the oxidation and adsorption by the plasma and catalyst. The synergistic reaction of the plasma and catalyst was more effective at low temperatures, resulting in a reduction in a lowered light-off temperature.

Hydroxyl Radical Generation on Bubble Surface of Aqua-Plasma Discharge

The location of hydroxyl radical (OH*) generation in aqua plasma is investigated with the images of vapor bubble discharge in a conductive electrolyte (saline). A comparison of the visible-and UV-ray data taken from the Na+* and radical OH* reveals that Na+* is generated in both volume and surface of bubble while most of OH* is observed at the vapor surface. This result implies that the steamer-type of aqua plasma was generated in the vapor bubble covered over a metal electrode tip, and the charged particles disperse along the surface of the vapor bubble.

Production and decay mechanism of atmospheric pressure homogeneous discharge generated by two L-shaped electrodes

We investigated the characteristics of the discharge generated by an atmospheric pressure plasma reactor that used two L-shaped electrodes and was driven by bipolar pulses having opposite polarity. Due to the difference in the surface charge distributions on the electrodes, the discharge behaviours vary greatly between the rising and falling stages of the voltage pulse. In all cases, the plasma formed inside the reactor plays an important role in suppressing a filamentary mode outside the reactor, and hence, homogeneous discharge in He can be achieved under an open-air configuration.

Gas Temperature Effect on Discharge-Mode Characteristics of Atmospheric-Pressure Dielectric Barrier Discharge in a Helium–Oxygen Mixture

For a better understanding of gas temperature effects on plasma characteristics, a numerical study has been carried out for a dielectric barrier discharge (DBD) with a helium-oxygen mixture at atmospheric pressure. A one-dimensional time-dependent simulation code has been developed to solve continuity equations for plasma species and Poissons equation for electric field calculation for a parallel-plate DBD reactor. To include temperature effects, gas heating by enthalpy change and Joule heating with ionic current movement are considered in the helium-oxygen plasma including 13 species reacting with one another according to 34 reactions depending on the gas temperature. Varying the ambient temperature from 300 K to 500 K, the plasma characteristics are calculated for the temporal variations and spatial distributions of electric field and species densities in the DBD region, and the different features of discharge modes are described by the voltage-current characteristic curves. A glowlike mode, which typically shows the formation of cathode fall, Faraday dark space, negative glow, and positive column in the spatial distributions of electric field and plasma density, is found in the discharge at a low ambient temperature, while a Townsend discharge mode with moderate electric field intensity and lower electron density is characterized at higher ambient temperatures. The temperature-dependent reactions strongly influence the generation and loss of species in the DBD plasma, and the decomposition of O3 into O or O2 and the quenching of metastable helium by the resultant O or O2 play an important role in determining the distinct discharge mode in the DBD of a He-O2 mixture. Furthermore, it is understood that the discharge-mode transition is controllable by the coupled effects of oxygen additive concentration, frequency, and gas temperature. A small amount of O2 additive or a high-frequency operation exhibits a glow mode in a specific range of ambient temperature, of which reason can be explained by density variation and quenching of helium metastable species caused by the produced oxygen-related species.

Methane activation using Kr and Xe in a dielectric barrier discharge reactor

Methane has interested many researchers as a possible new energy source, but the high stability of methane causes a bottleneck in methane activation, limiting its practical utilization. To determine how to effectively activate methane using non-thermal plasma, the conversion of methane is measured in a planar-type dielectric barrier discharge reactor using three different noble gases—Ar, Kr, and Xe—as additives. In addition to the methane conversion results at various applied voltages, the discharge characteristics such as electron temperature and electron density were calculated through zero-dimensional calculations. Moreover, the threshold energies of excitation and ionization were used to distinguish the dominant particle for activating methane between electrons, excited atoms, and ionized atoms. From the experiments and calculations, the selection of the additive noble gas is found to affect not only the conversion of methane but also the selectivity of product gases even under similar electron temperature and electron density conditions.

Electrode length effect on the abatement efficiency of N2O in low-pressure plasma reactor

Summary form only given. Regulations on the emission of greenhouse gases have been made stricter worldwide for mitigating global warming. The semiconductor and display industries emit significant amounts of greenhouse gases, such as N₂O and F-gases. We investigated the electrode length effect on the abatement characteristics of N₂O in a low-pressure plasma reactor. N₂O is extensively used in SiO₂ thin film depositions, SiCl2 + 2N₂O → SiO₂(s) + 2N₂ + Cl₂, and its global warming potential (GWP) is 310 (GWP of CO2 = 1). The destruction and removal efficiency (DRE) of N₂O was evaluated by using Fourier transform infrared (FTIR) spectroscopy. The DRE of N₂O was reduced with increasing the N₂O flow rate or decreasing the pressure. A larger electrode length yields a higher DRE, especially for higher N₂O flow rate and lower pressure conditions. For understanding this phenomenon, the discharge characteristics were analyzed by using optical emission spectroscopy (OES). Molecular emissions from N₂(C-B) and N₂+(B-X) bands were measured together with atomic emissions from O I (777 and 844 nm) lines, by varying the electrode length. The reason for a larger electrode length to achieve a higher DRE was explained in terms of the plasma property and gas residence time.