• 대한전기학회논문지
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• 제34권9호
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• pp.355-360
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• 1985

In this paper, the discharge phenomena of high frequency glow discharge in organic vapor are basically investigted to establish the growth mechanism and preparation technique for organic thin film. According to the increasing of discharge frequency, the discharge firing voltage(Vs) of organic vapor decreases. The dependence of discharge voltage(Vd) on gas pressure is generally in accord with Paschen's Law and Vd decreases as gas flow rate become larger, but increases as dischange current density become higher. And the values of Vd in organic vapor are generally higher than those of inorganic gas.

• 설비공학논문집
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• 제12권2호
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• pp.181-189
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• 2000

The scroll compressor used for heat pump has a wide range of operation condition. To cover both heating and cooling modes, the operating Pressure ratio ranges from 1.5 to 6.8. Since the scroll compressor, however, is a type of compressor whose pressure ratio is fixed, some loss in the compression work is caused by the operation at the pressure ratio different from the built-in pressure ratio. A way of avoiding this problem is to introduce by-Pass holes in compression chambers, so that the compressed gas of pressure higher than the discharge pressure, yet not reached to the discharge port can be released earlier through the by-Pass holes. In this paper, an optimum Positioning of the by-Pass hole and the effect of the by-pass valve on the compressor performance are studied.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권12호
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• pp.673-678
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• 2000

The dielectric barrier discharge(DBD) is a common method to create a nonthermal plasma in which electrical energy is used to create electrons with a high average kinetic energy. The unique aspect of dielectric barrier discharges is the large array of short lifetime(10ns) silent discharges created over the surface of the dielectric. A silent discharge is generated when the applied voltage exceeds the breakdown voltage of the carrier gas creating a conduction path between the applied electrode and grounded electrode. As charge accumulates on the dielectric, the electric field is reduced below the breakdown field of the carrier gas and the silent discharge self terminates preventing the DBD cell from producing a thermal arc. In fact, the most significant application of dielectric barrier discharges is to generate ozone for contaminated water treatment. Therefore, experiments were perfomed at 1∼2[bar] pressure using a coaxial geometry single dielectric barrier discharge for ozone concentrations and energy densities. The main result show that the concentration and efficiency of ozone are influenced by gas nature, gas quantity, gas pressure, supplied voltage and frequency.

• 한국화재소방학회논문지
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• 제29권2호
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• pp.33-38
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• 2015

고압과 정량 흡상을 목적으로 클리어런스가 없는 초고압 회전용적형 헬리컬기어 펌프의 개발을 진행하였다. 펌프의 내부 압력과 토출 유속을 검증하기 위해 CFD 해석을 수행하였다. 이에 따라 FVM 기법으로 유동해석을 수행하였는데 클리어런스가 없는 완전히 밀폐된 형태의 FVM 유동해석은 격자가 연속하게 구성되지 않아 유체영역이 분리되어 정상적인 결과를 얻어낼 수 없었다. 이러한 문제로 격자 구성이 필요치 않은 MPS 기법으로 유동해석을 수행하였고, MPS 유동해석을 통해 펌프의 내부 압력과 토출 유속을 확인할 수 있었다. 로터의 회전속도 1,000 rpm에서 펌프 내부의 압력은 최소일 때 19.5 bar, 최대일 때 44.6 bar이고, 평균 압력은 33.9 bar로 확인되었다. 토출 유속은 최소일 때 64.5 m/s, 최대일 때 84.8 m/s이고, 평균 유속은 76.1 m/s로 확인되었다. 본 연구를 통해 클리어런스가 없는 해석 모델의 유동해석은 FVM 기법보다는 MPS 기법이 더 적합하였음을 확인할 수 있었다. 또한 초고압 회전 용적형 헬리컬기어 펌프의 압력의 변화에 따른 유속과의 관계를 본 연구를 통해 규명할 수 있었다.

• 한국진공학회지
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• 제21권6호
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• pp.301-311
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• 2012

결정질 태양전지 등의 도핑 공정에 적용하기 위한 플라즈마 제트 장치의 기초 방전 특성을 조사한다. 대기압에서의 아르곤 플라즈마 제트와 대기 압력변화에 대한 대기 플라즈마 제트, 그리고 아르곤 분위기 압력 변화에 대한 플라즈마 제트의 전류-전압은 전형적인 정상 글로우 방전의 특성을 갖는다. 대기압 플라즈마 제트의 방전 전압은 약 2.5 kV의 높은 전압이 요구되며, 대기 및 아르곤 플라즈마 제트는 200 Torr 이하의 낮은 압력에 대한 방전 전압은 약 1 kV가 된다. 도핑용 실리콘 웨이퍼에 조사되는 단일 채널 플라즈마 제트의 전류는 인가전압의 조정에 의하여 수 10~50 mA의 고 전류를 용이하게 얻는다. 플라즈마 제트를 웨이퍼에 조사하는 경우에 웨이퍼의 온도 상승은 정상상태에서 약 $200^{\circ}C$가 된다. 실리콘 웨이퍼에 도핑 용재인 액상의 인산을 도포하여 플라즈마를 조사한 결과 얻어진 인 원자의 도핑 분포는 플라즈마 제트 도핑의 가능성을 보여준다.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.179-190
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• 2011

The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.

• 한국자동차공학회논문집
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• 제15권6호
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• pp.1-8
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• 2007

Minimizing the cylinder wear and the consumption rate of cylinder oil in a large two-stroke marine diesel engine is of great economic importance. In Korea, authors first developed a motor-driven cylinder lubricator for a Wartsila Switzerland large two-stroke diesel engine. The characteristic of the developed product is that can control automatically the oil feed rate with a load fluctuation by the motor drive and the offset cam. For manufacturing the reliable and useful products, however, it is necessary to investigate further characteristics and to improve performances as a cylinder lubricator. In this study, the effects of pump motor speed, plunger stroke and cylinder back pressure on oil feed rate, maximum discharge and delivery pressures are experimentally investigated by using the electronically controlled quill injection system and distributer in the developed cylinder lubricator. It is found that the oil feed rates of electronic control and mechanical type quills with the in-cylinder back pressure are differently characterized by the role of accumulator, the viscous resistance of contact area, etc. It can be also shown that the maximum discharge pressure of the electronic control quill is lower than the mechanical type one but the maximum discharge pressure difference of two types decreased as plunger stroke is small, and the maximum delivery pressures of two types increased as plunger stroke, motor speed and back pressure are elevated but the maximum delivery pressure of mechanical type is higher than the one of electronic control type.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3003-3008
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• 2007

Critical nozzle has been frequently employed to measure the flow rate of various gases, but hydrogen gas, especially being at high-pressure condition, was not nearly dealt with the critical nozzle due to treatment danger. According to a few experimental data obtained recently, it was reported that the discharge coefficient of hydrogen gas through the critical nozzle exceeds unity in a specific range of Reynolds number. No detailed explanation on such an unreasonable value was made, but it was vaguely inferred as real gas effects. For the purpose of practical use of high-pressure hydrogen gas, systematic research is required to clarify the critical nozzle flow of high-pressure hydrogen gas. In the present study, a computational fluid dynamics(CFD) method has been applied to predict the critical nozzle flow of high-pressure hydrogen gas. Redlich-Kwong equation of state that take account for the forces and volume of molecules of hydrogen gas were incorporated into the axisymmetric, compressible Navier-Stokes equations. A fully implicit finite volume scheme was used to numerically solve the governing equations. The computational results were validated with some experimental data available. The results show that the coefficient of discharge coefficient is mainly influenced by the compressibility factor and the specific heat ratio, which appear more remarkable as the inlet total pressure of hydrogen gas increases.

• 공업화학
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• 제22권3호
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• pp.261-265
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• 2011

아르곤과 산소 대기압 플라즈마를 이용한 미생물인 E. coli의 살균효과를 분석하였다. 유전체 격막 방전 형태의 플라즈마 반응기는 아르곤과 산소 혼합기체에서 균일한 플라즈마 방전과 오존 생성에 효과적이었다. 직접적인 대기압 플라즈마 조사에 따른 E. coli의 살균처리 공정에서 산소에 대한 혼합비와 인가전력의 증가는 방전기체의 오존 발생농도를 높여 미생물의 살균효과를 증가시켰다. 반응기와 시료와의 거리는 살균효과를 증가하기 위하여 가급적 작게 하는 것이 효율적이었다. 본 연구를 통하여 대기압 플라즈마는 오존과 같은 산화촉진제의 발생으로 저온에서 E. coli와 같은 미생물을 효과적으로 살균할 수 있어 기존의 살균법을 대체 할 수 있는 차세대 살균기술로서의 개발 가능성을 확인 할 수 있었다.

• 한국분말재료학회지
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• 제11권4호
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• pp.328-332
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• 2004

Fe nanopowders were successfully synthesized by plasma arc discharge (PAD) process using Fe rod. The influence of chamber pressure on the microstructure was investigated by means of X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The prepared particles had nearly spherical shapes and consisted of metallic cores (a-Fe) and oxide shells (Fe$_{3}$O$_{4}$), The powder size increased with increasing chamber pressure due to the higher dissolution and ejection rate of H$_2$ and gas density in the molten metal.