• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2250-2264
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• 2006

In micro- and nanoflows, the Boltzmann distribution is valid only when the electric double layers (EDL's) are not overlapped and the ionic distributions establish an equilibrium state. The present study has numerically investigated unsteady two-dimensional fully-developed electroosmotic flows between two parallel flat plates in the nonoverlapped and overlapped EDL cases, without any assumption of the Boltzmann distribution. For the study, two kinds of unsteady flows are considered: one is the impulsive application of a constant electric field and the other is the application of a sinusoidally oscillating electric field. For the numerical simulations, the ionic-species and electric-field equations as well as the continuity and momentum ones are solved. Numerical simulations are successful in accurately predicting unsteady electroosmotic flows and ionic distributions. Results show that the nonoverlapped and overlapped cases are totally different in their basic characteristics. This study would contribute to further understanding unsteady electroosmotic flows in micro- and nanofluidic devices.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.533-540
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• 2000

Lightning impulse $(1.2/44[\mus])$ and damped oscillating impulse $(Osc./44[\mus])$ : 0.83[MHz]) breakdown characteristics in sulphur-hexafluoride/nitrogen (SF6-N2) mixtures were investigated. The predischarge currents were observed to clarify the breakdown mechanism. th experiments were carried out under nonuniform electric fields disturbed by a needle-shaped protrusion whose length and diameter are 10[mm] and 1[mm] at total gas pressure up to 0.5[MPa] with nitrogen concentrations varying from 5 to 20[%] in the mixture. The electrical breakdowns of SF6-N2 mixtures for both the positive and negative polarities develop with steplike pulses in leader mechanism and the breakdown voltage -time (V-t) characteristics were affected by the space charge. The voltage-time curves for the negative oscillating impulse voltage were extended over the longer time range. The minimum breakdown voltages for the negative lightning and oscillating impulse voltage were higher than those for the positive ones. in particular the positive breakdown voltages were independent of the gas pressure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.97-97
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• 2010

A new electric application method was developed to prepare epoxy/organoclay nanocomposite for the electrical insulation in the AC electric fields and it could be also used in the field of various viscous polymer/organoclay systems. The applied AC electric field condition was as follows; (1) inter-electrode distance: 40 mm, (2) application voltage: 3-11 kV, (3) frequency: 60~1,000 Hz, and (4) application time: 0~60 min. To characterize the epoxy/clay nanocomposite, WAXS and TEM analyses were confirmed. In order to explain how the organic modifier affects the exfoliation phenomena, a mechanism of the oscillating collision of the quaternary ammonium head was proposed and the effects of the AC voltage and frequency and the organoclay content were studied.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 추계학술대회 논문집 학회본부
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• pp.287-289
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• 1994

This paper deals with the planar-type electric field sensor which can measure the time-varying electric fields. The theoretical principle and design rule of the sensor are introduced, and also the calibration and application investigations are carried out. From the calibration experiments, the frequency bandwidth of the measurement system ranges from 160 [Hz] to 25 [MHz]. At a high voltage laboratory, the electric fields caused by the impulse voltage and oscillating transient voltage are measured by the proposed sensor. Obtained results are well agreement with the applied voltage waveforms.

• 한국진공학회지
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• 제12권S1호
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• pp.36-39
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• 2003

Field-domain dynamics and current self-oscillations are theoretically studied in quantum-well (QW) negative-effective-mass (NEM) $p^{+}pp^{+}$ diodes when the electric field is applied along the direction of the well. The origin of current self-oscillations is the formation and traveling of electric-field domains in the p-base. We have accurately considered the scattering contributions from carrier-impurity, carrier-acoustic phonon, and carrier-optic phonon. It's indicated that, both the applied bias and the doping concentration largely influence the current patterns and self-oscillating frequencies, which lie in the THz range for the NEM $p^{+}pp^{+}$ diode with a submicrometer p-base. The complicated field-domain dynamics is presented with the applied bias as the controlling parameter.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2315-2320
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• 2007

This paper presents an investigative study on the efficacy of a new physical water treatment (PWT) technology using an oscillating electric field to mitigate mineral fouling in heat exchangers. Parallel graphite electrode plates immersed in water were used to generate the electric field directly in water. Artificial hard water at 500 ppm hardness was used in all fouling tests. The inlet temperatures were maintained at 23.5${\pm}$0.5$^{\circ}C$ and 85${\pm}$0.5$^{\circ}C$ for cold and hot water sides, respectively. The results at a cold water-side velocity of 0.3 m/s showed a 16-60% drop in fouling resistances from the baseline test depending on the frequency of the electric field for the PWT-treated cases.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1999-2001
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• 2000

Impulse breakdown voltage characteristics of sulphur-hexafluoride/nitrogen ($SF_{6}-N_{2}$) mixtures were presented. The applied voltages were the positive and negative lightning impulse (1.2/44${\mu}s$) and oscillating impulse ($0.4{\mu}s$/2.08MHz) voltages. The predischarge current was observed to clarify the breakdown mechanism. The electrode system was consisted of plane to plane configuration with a needle-shaped protrusion whose length and diameter are 10mm and 1mm. The measurements were carried out at the gas pressure of mixtures up to 0.5MPa with nitrogen concentrations varying from 5 to 20%. The electrical breakdown in $SF_{6}-N_{2}$ mixtures develops with steplike pulses in leader mechanism. The minimum breakdown voltages for the negative lightning and oscillating impulse voltages were higher than those for the positive.

• 센서학회지
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• 제4권1호
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• pp.15-20
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• 1995

본 논문은 시변전장을 측정할 수 있는 평판형 센서에 대하여 기술하였다. 광대역의 전장측정계를 구현하기 한 평판형 센서가 제안되었다. 측정계의 이론적인 원리와 설계방법에 대하여 제시하였으며, 교정실험 및 적용실험을 수행하였다. 교정실험을 통하여 전장측정계의 주파수대역과 감도는 $160\;[Hz]\;{\sim}\;25\;[MHz]$, 1.2 [mV/V/m] 이었다. 적용실험으로 고전압 실험실에서 임펄스전압과 진동성 과도전압에 의해 발생되는 전장을 제안된 측정장치로 측정하였으며, 측정결과는 우수하였다.

• 한국재료학회지
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• 제2권3호
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• pp.220-227
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• 1992

전기유변유체(electrorheological fluid : ERF)는 크기가 $10^{-6}m$정도를 가진 분극성이 강한 입자 분말을 유전유체속에 혼합하여 만든 콜로이드용액으로서 외부전기 장에 의하여 액체상태로부터 겔(gel)상태로 상태변환을 한다. 상태변환과정은 가역과정이며 $10^{-3}$초 정도의 빠른 시간내에 이루어진다. 본 논문에서는 주기적응력이나 주기적 변형이 가해지는 강제진동실험을 통하여 ERF의 점탄성 특성을 조사하였다. 점탄성은 복소수로서 실수부인 동적전단탄성율(storage shear modulus, G')과 허수부인 동적손실율(loss modulus, G")의 합으로 표현된다. 동적전단탄성율은 강제진동의 진폭과 주파수의 함수로 외부전기장에 의하여 크게 변화되었으나 손실계수(loss factor, ${\eta}=G"/G'$)는 진동의 진폭, 진동수 및 외부전기 장에 거의 독립적이었다. 실험(1)은 강제진동의 진폭을 고정하고 진동수를 변화하는 방법(frequency sweep)과 실험(2)는 진동 진폭을 변화시키는 방법(amplitude sweep)으로 실행했다. 본 실험에서는 cornstarch입자를 corn oil에 혼합한 것과 zeolite입자를 silicone oil에 흔합한 콜로이드 용액이 ERF로서 사용되었으며 인가된 전기장은 약$(1~3){\times}10^6V/m$의 직류전기장이 가하여졌다.기장이 가하여졌다.

• Tribology and Lubricants
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• 제14권2호
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• pp.42-48
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• 1998

Electro-Rheological (ER) fluid is a class of functional fluid whose apparent viscosity can be varied by the applied electric field strength. The ER fluid is classified into two types; one is a dispersive fluid and the other is a homogeneous. Dispersive ER fluid is a colloidal suspension of fine semiconducting particles in a dielectric liquid and liquid crystal (LC) is classed as homogeneous type ER fluid. LC has been originally developed for some electronic display devices. Various mechanical components applying ER fluid have been developed, and the their performance typically depends on the characteristics of ER fluid which have generally been evaluated by a rotational viscometer. However, the ER fluid introduced into various mechanical components undergoes not only simple shear flow but press flow or oscillating flow. For the evaluation of ER fluid, the authors developed an reciprocating type viscometer. The amplitude is controlled on 5 mm at the frequency from 50 to 1000 Hz. In the present paper, the performance of several types of ER fluid is evaluated by the reciprocating type viscometer and compared with those evaluated by a rotational viscometer.