• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2004.05a
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• pp.72-84
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• 2004

반도체 집적도가 높아지고 웨이퍼가 대구경화 됨에 따라 새로운 이송 장비의 개발이 필요하게 되었다. 본 연구에서는 이송장비의 새로운 개념인 공기부상 방식의 낱장이송 시스템을 설계하고 부상 노즐의 크기에 따른 부상 높이를 평가하였으며 그 결과 동일한 부상용 유량을 사용할 경우 0.5 mm 보다 0.8 mm 노즐이 부상 높이가 더 높고 에너지 절약적인 측면에서 유리함을 밝혔다. 또한 웨이퍼 이송용 추진 노즐의 배치에 따른 웨이퍼 이송 속도의 변화를 측정하여 동일 유량에서 추진속도가 훨씬 증가된 형상인 Type B(노즐 집중형)를 결정할 수 있었으며, 제조장비와 이송장비를 연결시켜주는 인터페이스에서의 웨이퍼 안정성을 평가한 결과 평균 16초 이내에 매우 안정된 공기부상 방식의 웨이퍼 낱장이송 시스템을 구현할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.639-646
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• 2012

The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1886-1896
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• 1991

This paper presents a method to predict the flying height of the head slider in a hard disk drive. Quantitative predicts of the flying height according to the variations of the external load and the disk velocity have been done by numerical computation. In addition, the magnitude of the external load to keep flying height constant were also suggested. The Modified Reynolds' equation driven from hydrodynamic lubrication theory under slip flow condition was used to describe air-bearing system under the slider. To solve the equation, a Finite Volume Method (FVM) has been applied. To determine the final minimum flying height and pitch angle of the head slider, the Secant iteration method is used which update initial guess of the minimum flying height and pitch angle of the slider. In this study, the model head slider has been selected from a real hard disk drive which is equipped in many commercial personal computers. As a result, as the disk velocity increases at constant external load, the minimum flying height and the pitch angle increase due to the in crease of the air-bearing force at the bottom of slider.

• Journal of the Korean Society for Railway
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• v.19 no.2
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• pp.135-144
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• 2016

It is essential to lighten the weight of switch girders in order to reduce their costs of manufacturing and make it easier to use them in construction. Lightening the weight of switch is also important to the Maglev 3-way switches system, however, the design variables should be considered very carefully if lightening is to be applied to the system, because these variables are vitally related to the levitation stability. Because Urban Maglev trains have a structure in which train bogie wraps around the guiderail, the adjustment of a girder's height is a possible way to reduce the weight. The safety of the application of this concept is ensured by repeated experiments in a test bed, however, due to a lack of space and budget limits, the design parametric study for the system model can substitute for actual application. The purpose of this paper is to study the design parameters that are concerned with levitation stability while a Maglev train is running on the Maglev 3-way system depending on the weight of the switch girders. In this study, switch girder weight is reduced by adjustment of girder height and girders are and modeled as a flexible body. The effect of the adjustment of girder height on the levitation stability can be analyzed by comparing the velocity of the train when it passes the switch girders, with the lateral gap, and the levitation gap which are obtained from the co-simulation of the Maglev train's dynamics model and flexible switching system. The results of this research will be used to design a Maglev switch.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.75-81
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• 2012

Autoignited lifted flames in laminar jets with hydrogen-enriched methane fuels have been investigated experimentally in heated coflow air. The results showed that the autoignited lifted flame of the methane/hydrogen mixture, which had an initial temperature over 920 K, the threshold temperature for autoignition in methane jets, exhibited features typical of either a tribrachial edge or mild combustion depending on fuel mole fraction and the liftoff height increased with jet velocity. The liftoff height in the hydrogen-assisted autoignition regime was dependent on the square of the adiabatic ignition delay time for the addition of small amounts of hydrogen, as was the case for pure methane jets. When the initial temperature was below 920 K, where the methane fuel did not show autoignition behavior, the flame was autoignited by the addition of hydrogen, which is an ignition improver. The liftoff height demonstrated a unique feature in that it decreased nonlinearly as the jet velocity increased. The differential diffusion of hydrogen is expected to play a crucial role in the decrease in the liftoff height with increasing jet velocity.

• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.1-8
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• 2000

The effects of nozzle arrangements, nozzle distances and fuel flowrates on the flame stabilities such as flame length, liftoff height and blowout characteristics are investigated experimentally. Three nozzle arrangements - diamond 4 nozzle, linear 5 nozzle, cross 5 nozzle- are used. Flame interactions result in the increase of the blowout flowrates and constant turbulent liftoff heights. The flames separated about 10 nozzle diameters are sustained as nozzle attached flames to the higher fuel flowrates than the other separation cases. Normally flames are extinguished at the lifted states. Blowout flowrates are affected by the nozzle configuration, nozzle seperation distance. Blowout flowrates for the diamond- or cross- shaped nozzle arrangements are parabolic function of nozzle distances. Maximum blowout flowrates for the 5 nozzle configuration case except linear one is about 2.9 times that of single equivalent nozzle case. Turbulent liftoff heights are not function of flowrates for the interacting flames.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.461-466
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• 2001

The characteristics of nonpremixed interacting flames are investigated in the parameter of nozzle configuration and nozzle separation distane, s. Three nozzle arrangements - diamond 4 nozzle, linear 5 nozzle and cross 5 nozzle- are used. When s is about 10 nozzle diameter, flames lift from the nozzle at the highest fuel flowrate compared with the other s cases. Normally flames are extinguished at the lifted states. Flowrates when blowout occurs are affected by the nozzle configuration, nozzle seperation distance. Blowout flowrates for the diamond- or cross-shaped nozzle cases are parabolic function of s. For 5 cross nozzle case, flames extinguished at 3.3 times higher flowrate than that of single equivalent area nozzle. Turbulent liftoff heights are not function of flowrates for these cases.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2006.05a
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• pp.317-320
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• 2006

20500 rpm에서 10분 교반까지 계면높이는 감소하였으나 10분 이상의 시간에서는 계면 높이가 증가하는 경향을 나타내었으며, 슬러지 농도도 10분까지 경향을 농축농도가 증가하지만 그 이상의 교반시간에서는 농도가 서서히 감소되는 경향을 나타내었다. Homogenizer의 교반에 의한 최적조건에서의 부상효율은 약 10%의 효과가 있는 것으로 나타났다. Image analyser로 교반하지 않은 경우와 교반한 경우 슬러지의 sauter mean diameter를 측정한 결과 각각 631 $\mu$m와 427 $\mu$m로 나타나 슬러지 플록의 입경이 줄어든 것으로 나타났다. 슬러지의 함수율은 10분의 교반시간까지 조금 감소하였으나 10분 이상의 교반시간에서는 슬러지 함수율이 증가하여 60분에는 99.1%까지 증가하였다.

• Journal of Sensor Science and Technology
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• v.11 no.6
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• pp.365-370
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• 2002

The jumping ring apparatus described in this study is used to demonstrate and educate the effects of electromagnetic induction. Placing an aluminum ring over the core and switching on AC source causes the ring to jump in the air due to induced currents in the ring producing a magnetic field opposed to that produced in the core. This force is a function of flux density, ac current of ring and levitated height of the ring. Using photo sensor arrays, detect the ring position and represent the position of the ring to analog voltage for an education performance. This paper presents modelling of the jumping ring system and shows how does control signal generate in order to follow desired position.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.56-63
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• 2018

In low swirl combustors the flame is lifted above the nozzle to achieve balance between the flame speed and velocity field at the exit of the nozzle. Characterization of the flame liftoff height is important because it affects the stability of the combustor and degradation of the nozzle material. In experiments, a counter-intuitive trend of flame liftoff heights with respect to inlet velocities was observed. To elucidate the complicated flow field in a low swirl combustor having swirl vanes and a turbulence generator, a series of numerical simulations of non-reacting flows was conducted by varying the inlet velocity. The flow structures at the exit of the nozzle with respect to the inlet velocities are investigated to support the observation in the experiments.