• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.585-588
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• 2008

Thermal mixing phenomena in a Y-type microchannel were investigated using a micro-PIV. Two inlet reservoirs of the microchannel were controlled individually so that the characteristics of thermal mixing in the channel with temperature difference were compared with those without the difference. The velocity field in the mixing process was measured using the micro-PIV system that includes an ICCD (Intensified CCD) camera. The mixing area and uniformity were also analyzed. It is observed that the flow fluctuation in spanwise direction is induced by temperature difference, which enhances mixing process in microchannels.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2811-2816
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• 2007

We conducted a numerical study of AC-electroosmotic (alternating current) effect on the fluid flow and mixing in a 3-D microchannel. The microchannel used as an efficient micro-mixer is composed of a channel and a series of pairs of electrodes attached in zigzag pattern on the bottom wall. The AC electric field is applied to the electrodes so that a steady flow current takes place around the electrodes. This current is flowing across the channel and thus contributing to the mixing of the fluid within the channel. We performed numerical simulations by using a commercial code to obtain a steady flow field. This steady flow is then used in evaluation of the mixing performance via the concept of mixing index. It was found that good combination of two kinds of electrode, which gave us a good mixing, is not simple harmonic. And when the length ratio of these two kinds of electrode is 2:1, we can get the best mixing effect.

• 동력기계공학회지
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• 제11권3호
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• pp.16-21
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• 2007

Three dimensional numerical study was carried out to investigate the effect of aspect ratio on microchannel flow. We considered five straight rectangular channels with aspect ratios (height/width) 0.2, 0.4, 0.6, 0.8 and 1.0. Nitrogen gas flow was investigated for both slip and noslip wall boundary conditions. Isothermal wall condition was assumed. We used control volume method for this simulation. The slip velocity increases with the increase of aspect ratio. Friction coefficient decreases with the increase of aspect ratio. Slip friction coefficient is lower than noslip friction coefficient. Mass flow rate of slip model is higher than that of noslip model. We compared our results with the experimental result reported in the literature. The agreement was good.

• 대한기계학회논문집B
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• 제28권5호
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• pp.587-593
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• 2004

In this paper, flow characteristics of plasma flow in a micro-tube were investigated experimentally using micro particle image velocimetry(micro-PIV). For comparison, the experiments were repeated for deionized(DI) wale. instead of plasma. Both velocity profiles of plasma and do-ionized water are well agreed with the theoretical velocity distribution of newtonian fluid. We also carried out generating plasma-in-oil droplet formation at a Y-junction microchannel. In order to clarify the hydrodynamic aspects involved in plasma droplet formation, Rhodamine-B were mixed with plasma only for visualization of plasma droplet. With oil as the continuous phase and plasma as the dispersed phase, plasma droplet can be generated in a continuous phase flow at a Y-junction. For given experimental parameters, regular-sized droplets are reproducibly formed at a uniform flow conditions.

• 전기화학회지
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• 제16권1호
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• pp.39-45
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• 2013

물 관리는 저온에서 작동하는 고분자전해질 연료전지의 성능에 큰 영향을 미친다. 가스확산층(gas diffusion layer, GDL)은 반응 가스를 촉매층의 반응영역으로 확산시키는 역할을 한다. 연료전지의 작동온도가 $60{\sim}80^{\circ}C$이기때문에, 고전류 밀도에서 생성된 물은 액적을 형성한다. 만약 생성된 물이 적절하게 제거되지 않는다면, GDL 내의 기공을 막게 되고 연료전지 성능이 저하된다. 본 연구에서는 플러딩 현상을 막기 위해 마이크로채널 GDL 을 제안하였다. 기존 GDL과 마이크로채널 GDL을 3차원으로 구현하여 공기 속도, 물속도, 접촉각의 변화에 따른 물의 이송을 연구하였다. 전산해석 결과를 통해 마이크로채널 GDL에서는 낮은 유동 저항으로 인해 물이 빠르게 제거되는 것으로 나타났다. 그러므로, 마이크로채널 GDL이 가스채널과 GDL 내부의 물 제거에 효율적임을 알 수 있다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.44.5-45
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• 2008

• 대한기계학회논문집B
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• 제35권1호
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• pp.61-66
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• 2011

새롭게 제안된 형상의 마이크로채널 PCHE는 기존의 상용 열교환기에 비해 고성능, 고효율의 특성을 보이며 열교환을 수행한다. 본 연구에서는 I, Wavy, Beehive, Surf, I-Wavy, I-Beehive, I-Surf 의 형상을 갖는 다양한 마이크로채널을 모델링하였다. 질량유속 변화에 따른 다양한 마이크로채널 내 유체의 유동특성, 열전달, 압력강하를 살펴보았고 그 결과는 마이크로채널의 열전달 능력을 향상시키는데 이용된다. I 채널은 새롭게 적용된 채널 형상과의 성능비교를 위해 해석을 수행하였다. 다양한 레이놀즈수 변화 하에서 고온측과 저온측 유체는 대향류 형태로 열교환이 이루어지도록 하였다. 수치해석 결과 Surf 형상이 다른 형상들보다 열교환 성능이 우수함을 확인하였다.

• 대한기계학회논문집B
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• 제30권1호
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• pp.1-7
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• 2006

The characteristics of micro gaseous flows in microchannels have been analyzed in view of flow resistance using the direct simulation Monte Carlo (DSMC) method which is a molecule-based numerical modeling technique. For this purpose, a DSMC code where the pressure boundary condition was specified at the inlet and outlet, has been developed and the results of simulations showed satisfactory agreements with the analytic solution in the slip flow regime. (0.01 < Kn < 0.1) By varying the height and length of the microchannel, the effect of pressure difference between the inlet and outlet was examined. The present computation indicates that the curvature in pressure distribution along the channel increases due to the effect of compressibility when the pressure difference increases. To obtain the flow resistance regardless of the channel dimensions, a standard curve is devised in the present study by introducing the concept of unit mass flowrate and unit driving pressure force. From this curve, it is shown that in micro flows, a significant deviation from the laminar incompressible flow occurs by reducing the flow resistance.

• 동력기계공학회지
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• 제18권6호
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• pp.207-214
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• 2014

Mass and flow resistance in a square ribbed microchannel have been studied numerically using the Lattice Boltzmann Method. It has been build up on two dimensional nine velocity vectors model with single relaxation time method called the Lattice Bhatnagor-Gross-Krook model. To analyze the roughness effect on the flow resistance namely the friction factor and mass flow has been discussed at the slip flow regime, $0.01{\leq}Kn{\leq}0.10$, where Kn is the Knudsen number. The wall roughness is considered by square microelements with a relative roughness height up to maximum 10% of channel height. The velocity profiles in terms of streamlines near the riblets are demonstrated to be responsible for the roughness effect. It is found that the roughness effect leads to increase the flow resistance with roughness height but it is decreased significantly with increasing the space between two roughness elements as well as the Knudsen number. In addition, the mass flow decreased linearly with increasing both roughness height and gap but significantly changed at the slip flow regime.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.44-52
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• 2001

A micro-PIV(particle image velocimetry) measurement has been conducted to investigate flow fields in such microfluidic devices as microchannels and micronozzle. The present study employs a state-of-art micro-PIV system which consists of epi-fluorescence microscope, 620nm diameter fluorescent seed particles and an 8-bit megapixel CCD camera. Velocity vector fields with a resolution of $6.8\;\times\;6.8{\mu}m$ has been obtained, and the attention has been paid on the effect of varying measurement conditions of particle diameter and particle concentration on the resulting PIV results. In this study, the microfluidic elements were fabricated on plastic chips by means of MEMS processes and a subsequent molding process. Flow fields in a variety of microchannels as well as micronozzle have been investigated.