• Journal of the Korean Society of Visualization
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• v.17 no.1
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• pp.43-52
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• 2019

'Ionic wind' is phenomenon induced by corona discharge which occurs when large electric potential is applied to electrodes with high curvature. The ionic wind has advantage that it could generate forced convective flow without any external energy like separate pump. In this study, 'pin-mesh' arrangement is utilized for experiments. First, optimization of configuration is conducted with local momentum of ionic wind behind the mesh. Empirical equation for prediction about velocity profile was derived using the measured results. Secondly, the enhancement of mass transfer rate of acetone with ionic wind was analyzed. Also, the drying efficiency using a fan which has same flow rate was compared with ionic wind for identification of additional chemical reaction. At last, the drying process of organic solvent was visualized with image processing. As a result, it was shown that the use of ionic wind could dry organic matter four times faster than the natural condition.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.3
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• pp.311-318
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• 2001

The application of a pulsed power system is being extended to a environmental and industrial fields. The non-dissolution waste water pollutants from industrial plants can be processed by applying high voltage pulses with a fast rising time (a few nanoseconds) and short duration (nano to microseconds) in a pulsed corona discharge reactor. The nano-pulse generator with a magnetic switch has been developed. Its corona current in load can be adjusted by pulse width and repetition rate. we investigated the performance of the nano-pulse generator using the dummy load which is composed of resistor and capacitor equivalent to the actual reactor. This paper descibes the electrical characteristics of the nano-pulse generator that produces a 300 ns pulse at maximum repetition rate of 400 pps with a voltage of 40 kV across a $640{\Omega}$ load. In this paper we briefly discuss a configuration of system and test results.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.2
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• pp.120-124
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• 2000

In this paper, the effect of magnetic field was measured on NOx(NO+NO2) removal and consumption power for wire-plate plasma reactor with magnetic field applied to electric field vertically. NOx of the simulated diesel engine flue gas were removed by the corona discharge generated by DC, AC and Pulsed voltages in wire-plate reactor. Consumption power increased with discharge voltage. However, when magnetic field was applied to electric field vertically, consumption power slightly decreased. NOx removal rate and arc transition voltage for plasma reactor with magnetic field were higher than those for plasma reactor without magnetic field. Consumption power decreased, however NOx removal significantly increased, when water vapour bubbled by dry air was put into simulated flue gas.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.2
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• pp.79-85
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• 2001

A conventional electrolyzing cell has been made by an ion exchange membrane inbetween parallel plate electrodes. A low dc voltage is applied to the electrodes for electrolyzing and the efficiency is remained in low. in this study, a novel electrolyzing cell with a pair of slit-type third electrodes installed inbetween parallel plate electrodes has been proposed and investigated experimentally. And pulse power wa supplied to between each electrodes. This slit type of third electrodes can concentrate the strong electric fields at the every its edges to accelerate the electrolyzing powers, and to generate oxygen bubble discharges for generating oxidants. And moreover the slits eliminate the space charge limiting action and the temperature of the water by leaking out through the slits from electrolyzing region to outside of the main electrode region. As a result, it was found that a strong electorzed water of pH 2.8 and pH 10.5 and oxidants dissolved water of 1 [ppm] in acidic water were obtained with a tap water fed at the electric current of 2 [A], which however were several times higher oxidant and ion concentration quantity compared with the conventional cell.

• Journal of Power Electronics
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• v.16 no.1
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• pp.84-92
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• 2016

Compared with Si MOSFETs, the GaN FET has many advantages in a wide band gap, high saturation drift velocity, high critical breakdown field, etc. This paper compares the electrical properties of GaN FETs and Si MOSFETs. The soft-switching condition and power loss analysis in a flyback-forward high gain DC/DC converter with a GaN FET is presented in detail. In addition, a comparison between GaN diodes and Si diodes is made. Finally, a 200W GaN FET based flyback-forward high gain DC/DC converter is established, and experimental results verify that the GaN FET is superior to the Si MOSFET in terms of switching characteristics and efficiency. They also show that the GaN diode is better than the Si diode when it comes to reverse recovery characteristics.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.40.3-40.3
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• 2019

Our recent observations of the Sun through strong spectral lines have revealed several important properties of the three-minute umbral oscillations inside sunspots -- the oscillations of intensity and Doppler velocity with periods of 2 to 3 minutes. The oscillations usually occur in the form of a time series of oscillation packets each of which lasts 10 to 20 minutes, not as continuous trains. Each oscillation packet is characterized by a singly peaked power spectrum of velocity oscillation. The oscillations propagate in the vertical direction from the photosphere to the corona. In the upper chromosphere, they develop into shocks that eventually collide with the transition region. When shocks propagate along a highly inclined direction, the merging of two successive shocks can take place. Once they enter the corona, they change to linear compressional waves. In the image plane, the three-minute oscillations propagate with high speeds in the transverse direction as well, usually propagating radially outwards from a point, and sometimes accompanying spiraling patterns of Doppler velocity. These observational properties can be theoretically explained by postulating the spatio-temporally localized source of fast MHD waves at a depth of about 2000 km below the surface, the excitation of slow MHD waves via mode conversion near the photosphere, and the resonance of the slow waves in the photospheric layer below the temperature minimum, and the nonlinear development of slow waves in the chromosphere.

• Journal of fish pathology
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• v.33 no.1
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• pp.63-69
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• 2020

Fish culture is constantly threatened by various infectious diseases which are largely transmitted by water. Plasma technology is being used to sterilize polluted water in many industries. In this study, two bacterial pathogens Aeromonas salmonicida and Streptococcus iniae, and a virus (viral hemorrhagic septicemia virus, VHSV) were subjected to plasma water that was produced by a corona discharge system. Growth of A. salmonicida was greatly inhibited from 10^5.61 CFU/ml in positive control to 10^3.51 CFU/ml in treated group by only 60 sec contact with plasma water. Similarly, S. iniae was inhibited from 10^5.85 CFU/ml to 10^3.40 CFU/ml. VHSV titer also decreased from 10^4.1 TCID₅₀/ml to 10^1.45 TCID₅₀/ml by the same treatment. Activation of water by the plasma was confirmed by the existence of ozone in the plasma water. These results suggest that plasma water could efficiently disinfect fish pathogens, possibly by the action of reactive oxygen species contained in the plasma water.

• Journal of The Korean Astronomical Society
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• v.51 no.2
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• pp.27-36
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• 2018

In a solar coronagraph, the most important component is an occulter to block the direct light from the disk of the sun. Because the intensity of the solar outer corona is $10^{-6}$ to $10^{-10}$ times of that of the solar disk ($I_{\odot}$), it is necessary to minimize scattering at the optical elements and diffraction at the occulter. Using a Fourier optic simulation and a stray light test, we investigated the performance of a compact coronagraph that uses an external truncated-cone occulter without an internal occulter and Lyot stop. In the simulation, the diffracted light was minimized to the order of $7.6{\times}10^{-10}I_{\odot}$ when the cone angle ${\theta}_c$ was about $0.39^{\circ}$. The performance of the cone occulter was then tested by experiment. The level of the diffracted light reached the order of $6{\times}10^{-9}I_{\odot}$ at ${\theta}_c=0.40^{\circ}$. This is sufficient to observe the outer corona without additional optical elements such as a Lyot stop or inner occulter. We also found the manufacturing tolerance of the cone angle to be $0.05^{\circ}$, the lateral alignment tolerance was $45{\mu}m$, and the angular alignment tolerance was $0.043^{\circ}$. Our results suggest that the physical size of coronagraphs can be shortened significantly by using a cone occulter.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.8
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• pp.67-74
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• 2008

In this paper we describe discharge characteristics between needle-to-plane electrodes in water in various conditions such as different impulse voltages, polarities and water resistivities. Streamer corona is initiated at the tip of needle electrode and propagates toward plane electrode, and it experiences the final jump across the test gap. The branched channels of streamer coronas for lower water resistivities are much thicker and brighter than those for higher water resistivities at the same level of applied voltage. The negative streamer coronas not only have more branches but also widely spread out compared to the positive streamer coronas. A number of pulse-like currents ranging from some hundreds mA to a few A after streamer corona onset were produced with discharge developments. The time-lags-to breakdown for the positive polarity were remarkably shorter than those for the negative polarity. The pre-breakdown energy supplied into the test gap was inversely proportional to water resistivity.

• The Journal of the Korea Contents Association
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• v.20 no.12
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• pp.112-122
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• 2020

This study analyzed how KBS's 'Type and Format', 'Professionalism' and 'Infectious Disease-related Issues' appear in the media news related to Corona-19 under the three periods of 'discovery', 'diffusion' and 'recovery'. According to an analysis of a total of 473 media news, In all three periods, 'Straight Report' and 'Information Delivery Frame' were high to inform the truth of the infectious disease. In addition, the 'transmission of facts' frame was more used than the emotional transmission in reporting the risk situation. However, the proportion of 'moral evaluation frames' in the second phase was relatively high, and the proportion of non-professional journalists was still overwhelmingly higher than professional journalists. Meanwhile, infectious disease-related issues had the most content on 'infection control', and relatively little information on how to deal with them. Based on the above findings, this study suggested the implications of 'Increased in-depth and professional press coverage', 'Refrain from moral evaluation frames' and 'a comprehensive presentation of various infectious disease-related information'.