• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.220-226
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• 2006

The effect of electric fields on the propagation speed of tribrachial flames has been investigated in a coflow jet by observing the transient flame propagation behavior after ignition. Without having electric fields, the propagation speed of tribrachial flame edges showed a typical behavior by having an inverse proportionality to the mixture fraction gradient at the flame edge. The behavior of flame propagation with the electric fields was investigated by applying high voltage to the central fuel nozzle and the enhancement of propagation speed has been observed by varying the applied voltage and frequency for AC electric fields. The propagation speed of tribrachial flame was also investigated by applying negative and positive DC voltages to the nozzle and similar improvements of the propagation speed were also observed. The propagation speeds of tribrachial flames in both the AC and DC electric fields were correlated well with the electric field intensity, defined by the electric voltage divided by the distance between the nozzle electrode and the edge of tribrachial flames.

• 대한기계학회논문집B
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• 제35권3호
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• pp.321-330
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• 2011

본 연구는 전선화염의 전파특성에 직류전기장이 미치는 영향에 대한 실험적 연구이다. 화염전파는 은 0에서 ${\pm}7kV$ 범위의 음극과 양극의 전기장을 인가하여 실험되어졌다. 본 연구를 통해 앞선 전선화염 전파에 영향을 미치는 교류전기장 효과에 관한 연구결과와 비교하여 관찰된 다양한 화염 모양 변화의 원인을 알아보고, 화염 전파 속도의 가속특성에 대해서도 논의하고자 한다. 직류전기장의 인가가 전선화염에 미치는 영향은 크지 않지만 이온풍 효과에 따른 미미한 영향은 존재하며, 이것은 온도 균형 메커니즘과 연료 증발기체 분사 효과로 설명 될 수 있다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.253-259
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• 2006

The effect of DC electric fields on the flame extinction was investigated experimentally in counterflow configurations for the methane/oxygen/nitrogen diffusion flame. The electric fields was applied by connecting the high voltage and ground terminals to the upper and lower burners, respectively. In case of having electric fields, several modes of flame extinction was observed according to the electric field intensity and strain rate defined by the exit velocity. To visualize and characterize the flame structure and intensity, planar LIF technique was adopted for OH radicals. Consequently, several length scales, including the flame width, thickness, and height from the burner tip, were introduced to explain the various flame behaviors and to characterize the flame extinctions. It was found that the variation of flame width and the chemical reaction are strongly related to a critical electric field intensity, thus the various modes of diffusion flame extinction could be observed due to the electric fields.

• 한국연소학회지
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• 제16권3호
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• pp.41-51
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• 2011

In this paper, we describe the behavior of two self-excitations in laminar attached free-jet flames under the influence of DC electric fields, one of buoyancy-driven and the other of diffusion-thermal instability, established from the horizontal and vertical injection. In the horizontal injection with removed buoyancy effect, oscillating flames with the frequency of 1.3 - 7.4 Hz were observed in a certain condition with Lewis number more than unity. On the other hand, it was appeared Lewis number induced self-excitation as well as buoyancy-driven self-excitation in the vertical upward injection with DC electric fields. This behavior had frequency range of 1.6 - 9.4 Hz and was exhibited to attribute the buoyancy effect. Finally, a well-defined division about two self-excitations having similar frequency range is briefly discussed.

• 조명전기설비학회논문지
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• 제29권11호
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• pp.74-81
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• 2015

In the measurement of atmospheric static electric field, it is important to know characteristics of corona discharges caused at the tip of test electrode. This paper presents the fundamental data of DC corona discharges that occurred at the tip of a needle-shaped electrode placed in the homogeneous background electric field which simulates the atmospheric static field under thundercloud. The major characteristics of interest for this purpose are the polarity effect of corona discharges and the magnitudes and time intervals of corona current pulses. The experimental set-up consists of the plate-to-plate configuration with a needle-shaped protrusion, DC power supply, and voltage and current measuring devices. As a result of experiments, the polarity dependence of corona pulses is significantly pronounced. The time intervals between successive corona pulses in the negative polarity is much longer than those in the positive polarity. The time intervals for both polarities is drastically decreased as the applied electric field is increased. Also the magnitudes of the positive corona pulses are slightly changed with an increase in applied electric field, but those of the negative corona pulses are linearly increased with increasing the applied electric fields.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.137-143
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• 2006

The effect of electric fields on flame speed has been investigated experimentally by observing propagating premixed flames in a tube for methane/air mixtures. The flame speeds were measured in both the normal and micro gravity conditions to substantiate the measurements. The results show that the flame speeds were enhanced by both the AC and DC electric fields, as the flame approached to the high voltage electrode located on the one end of the tube. The enhancement of flame speed was proportional to the square root of the electric field intensity, defined as the voltage applied divided by the distance of flame from the high voltage electrode, when the electric field intensity is sufficiently large. When the electric field intensity was low, there existed critical intensities, below which the electric fields did not influence the flame speed. This critical electric field intensity correlated well with the flame speed.

• 한국연소학회지
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• 제21권3호
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• pp.1-6
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• 2016

The effect of applied electric fields on jet flow instability was investigated experimentally by varying the direct current (DC) voltage and the alternating current (AC) frequency and voltage applied to a jet nozzle. We aimed to elucidate the origin of the occurrence of twin-lifted jet flames in laminar jet flow configuration, which occur when AC electric fields are applied. The results indicate that a twin-lifted jet flames originates from cold jet instability, caused by interactions between negative ions in the jet flow via electron attachment as $O_2+e{\rightarrow}O_2{^-}$ when AC electric fields are applied. This was confirmed by experiments in which a variety of gaseous jets were ejected from a nozzle to which DC voltages and AC frequencies and voltages were applied, with ambient air between two deflection plates connected to a DC power source. Experiments in which jet flows of several gases were ejected from a nozzle and AC electric fields were applied in coflow-nitrogen provided further evidence. The flow instability occurred only for oxygen and air jets. Additionally, jet instability occurred when the applied frequency was less than 80 Hz, corresponding to the characteristic collision response time. The effect of AC electric fields on the overall structure of the jet flows is also reported. Based on these results, we propose a mechanism to reduce jet flow instability when AC electric fields are applied to the nozzle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1647-1649
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• 2003

The electric fields of the sheath region in an argon do discharge were measured using a laser optogalvanic spectroscopy in a pressure range from 0.88 to 10 Torr, where collisions are significant in the sheath region. The sheath width is estimated as the position where the electric field becomes zero, and the pressure dependence of the measured sheath width was obtained to be $(pressure)^{-1/3}$. The measured electric fields agree well with one-dimensional simulation results but are slightly different from collisional sheath theory in the mobility limited region.

• 한국전기전자재료학회논문지
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• 제21권1호
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• pp.79-84
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• 2008

We are developing a small-sized high temperature superconducting magnetic energy storage (HTS-SMES) magnet with the nominal storage capacity of 600 kJ, which provides electric power with high quality to sensitive electric loads. Critical current and N-value of a high temperature superconductor with large current, which was selected for the development of the 600 kJ HTS-SMES magnet, were investigated in various oblique external magnetic fields. Based on the critical current and N-value measured for the short sample conductor, we discussed the DC V - I characteristic of a model coil fabricated with the same conductor of 500 m. The results show that the measured critical current and N-value of the conductor for parallel field are constant in external magnetic fields less than about 0.2 T. However, for oblique fields, its critical current and N -value abruptly decrease in all external magnetic fields. Moreover, the measured critical current of the model coil well agrees with the numerically calculated one based on the DC V - I characteristic measured for the short sample conductor. This suggest that losses and critical currents for an HTS-SMES magnet made up of a high temperature superconductor with anisotropic characteristic are predictable from the data of a short sample conductor.

• 마이크로전자및패키징학회지
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• 제21권4호
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• pp.111-115
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• 2014

다마신 구리 배선에서의 동적인 전기장에 따른 절연체 파괴거동을 연구하였다. DC, 단극성, 및 이극성 펄스 조건 중에서 절연체의 수명은 이극성 펄스 조건에서 가장 길었다. DC 및 단극성 펄스 조건에서는 절연체에 가해지는 전기장의 방향이 바뀌지 않지만 이극성 펄스 조건에서는 전기장의 방향이 반복적으로 180도 바뀌기 때문에, 이극성 펄스 조건에서는 절연체의 구리오염이 억제되고, 이로 인해서 절연체 수명이 이극성 펄스 조건에서 가장 긴 것으로 판단된다. 단극성 펄스 조건에서 펄스 주파수가 커질수록 DC 조건보다 절연체의 수명이 증가하였다. 이는 절연체 수명에 구리오염 뿐만 아니라 내재적인 절연파괴현상이 상당한 영향을 미치며, 절연체 분자결합파괴가 일어날 확률은 펄스 폭이 좁아질수록 감소한다고 판단된다.