• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.818-823
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• 2015

본 연구에서는 전산유체역학(CFD)을 이용하여 마이크로채널 내부의 Fischer-Tropsch(FT) 반응을 모사하였고, 나아가 반응채널의 너비와 높이, 냉각채널과의 거리 그리고 채널 사이 간격을 변수로 두고 채널 내부 온도에 대해 민감도 분석을 수행하였다. 마이크로채널 반응기는 채널 간의 열교환을 고려하기 위한 5개의 반응채널과 냉각채널을 대신한 냉각면으로 이루어져 있으며 채널의 높이와 너비를 포함한 변수들의 길이는 0.5 mm ~ 5.0 mm 범위에서 설정하였다. 반응물로는 $H_2$와 CO의 혼합기체($H_2/CO$ molar ratio=2)를 사용하였으며 반응기의 운전 조건은 $GHSV=10000h^{-1}$, 압력 20 bar와 온도 483 K($210^{\circ}C$)이다. 민감도 분석의 결과로 반응채널 내부의 최대 온도는 채널의 높이에 비례하며 너비에 대해서는 특정 길이 이상에서 영향을 받지 않는 것을 확인하였으며 이 중에 냉각채널과의 거리와 채널 사이 간격은 채널 내부 온도에 거의 영향을 미치지 않았다. 따라서 채널 레이아웃에서 반응채널의 높이는 짧을수록(약 2 mm 이하), 너비는 길수록(약 4 mm 이상) 열제거뿐만 아니라 생산량 측면에서 이득을 얻을 수 있었다.

• 한국유체기계학회 논문집
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• 제14권2호
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• pp.17-24
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• 2011

Temperature gradient focusing (TGF) of analytes via Joule heating is achieved when electric field is applied along a microchannel of varying width. The effect of varying width of the microchannel for the focusing performance of the device was numerically studied. The governing equations were implemented into a quasi-1D numerical model along a microchannel. The validity of the numerical model was verified by a comparison between numerical and experimental results. The distributions of temperature, velocity, and concentration along a microchannel were predicted by the numerical results. The narrower middle width and wider outside width of the channel having the fixed length contribute to improve the focusing performance of the device. However, too narrow middle width of the channel generates a higher temperature which can cause the problems including sample denaturation and buffer solution boiling. Therefore, the channel geometry should be optimized to prevent these problems. The optimal widths of the microchannel for the improvement on TGF were proposed and this model can be easily applied to lab-on-a-chip (LOC) applications where focusing is required based on its simple design.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1623-1628
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• 2008

A temperature gradient focusing (TGF) via Joule heating phenomenon was numerically studied. The governing transport equations are implemented into a quasi-1D numerical model to predict the resulting temperature, velocity, and concentration profiles along a microchannel of varying width under an applied electric field. The model is used to analyze the effects of varying certain geometrical parameters of a microchannel on the focusing performance of the device. We show the effects of varying width of the microchannel having a fixed length, and propose the optimal geometry of the device. This method can be easily implemented into lab-on-a-chip (LOC) applications where focusing is required based on its simple design.

• 한국수소및신에너지학회논문집
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• 제33권4호
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• pp.430-436
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• 2022

This paper presents the numerical model development of a microchannel heat exchanger in mobile air-conditioning and heat pump applications. The model has been developed based on the effectiveness-NTU method using a segment-by-segment modeling approach. State-of-art correlations are used for refrigerant- and air-side heat transfer coefficients and pressure drops. The calculated heat condenser capacities are in good agreement with experimental data, with an average difference of 1.86%. The current model can be used for microchannel condenser simulations under various operating conditions. It is anticipated to improve productivity in designing and optimizing microchannel heat exchangers with folded louver fin geometry.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1004-1009
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• 2003

Electroosmotic flow induced by an applied electrostatic potential field in microchannel is analyzed in this study. The electroosmotic flow is an alternative to pressure driven flow in microchannels, but the usage has been limited to the simple cases. In this study, We analyze electroosmotic flow driven by inhomogeneous surface charge on the channel wall. The surface charge varies along a direction perpendicular to the electric field in order to generate the electroosmotic flow. A numerical results substantiate the highly efficient mixing performance. It is highly the beneficial to fabrication process since only straight microchannel rather than complex geometry is enough to yield efficient mixing.

• 한국가시화정보학회지
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• 제9권2호
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• pp.21-26
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• 2011

Hydrodynamic focusing technique to generate focused flow has been used for flow cytometry in microfluidic devices. However, devices with circular capillary tubes made of glass are not suitable for flow visualization or optical signal detection because the rays of light are distorted at the curved interface. We devised a new acrylic chamber assembled with a pulled micropipette and a rectangular microchannel made of glass. This new channel geometry enabled us to visualize the three-dimensional (3D) flow characteristics with confocal imaging technique. We analyzed the 3D hydrodynamic focusing in a circular capillary tube and a rectangular microchannel over a practical range of flow rates, viscosities and pressure drops.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2658-2663
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• 2008

In the present study, we designed a microfluidic flatform that generates monodisperse droplets with diameters ranging from hundreds of nanometers to several micrometers. To generate fine droplets, T-junction and flow-focusing geometry are integrated into the microfluidic channel. Relatively large aqueous droplets are generated at the upstream T-junction and transported toward the flow-focusing geometry, where each droplet is broken up into the targeted size by the action of viscous stresses. Because the droplet prior to rupture blocks the straight channel that leads to the flow-focusing geometry, it moves very slowly by the pressure difference applied between the advancing and receding regions of the moving droplet. This configuration enables very low flow rate of inner fluid and higher flow rate ratio between inner and outer fluids at the flow-focusing region. It is shown that the present microfluidic device can generate droplets with diameters about 1 micrometer size and standard deviation less than 3%.

• Korean Chemical Engineering Research
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• 제52권6호
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• pp.826-833
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• 2014

해양 중소규모 가스전의 경제성에 대한 화두가 던져진 이후 전통 석유의 가격변동과 세계적인 환경규약 등에 맞물려 석유화학관련 산업계에서는 이를 효과적으로 대처하고 천연가스를 활용할 수 있는 공정을 개발하고자 하였다. 이에 Fischer-Tropsch 반응을 기반으로 하는 해상 GTL 공정(offshore gas-to-liquid process)이 제안되었고 부유시스템 platform으로 공정을 적용시키고자 마이크로채널 반응기가 떠오르고 있다. 본 논문에서는 단일 마이크로채널 반응기를 Fischer-Tropsch 반응을 기반으로 하여 Matlab과 ASPEN Hysys를 연동하여 모사하고 이로 얻어진 반응열을 도입해 상용 전산유체역학(computational fluid dynamics, CFD) 소프트웨어인 ANSYS fluent로 멀티 마이크로채널 반응기 모델을 제작하였다. 그리고 4가지의 설계변수인 냉각채널 넓이, 높이, 냉각채널과 반응채널의 간격, 냉각채널 간의 간격을 설정하고 이들의 변화에 따른 열유동을 3가지의 변수인 열유속, 냉각 및 반응채널의 최대온도의 변화를 시각화하여 그 경향성을 확인하였다. 경향성 분석 결과, 냉각채널의 넓이와 높이는 짧을수록 총 열유속이 높아졌으며 최대온도 역시 높아졌으나 냉각채널과 반응채널의 간격은 열유동에 거의 영향을 미치지 못하였다. 냉각채널 간의 간격은 짧을수록 총 열유속이 높아졌으며 최대온도는 낮아졌다. 따라서 적절한 냉각채널의 넓이와 높이를 제안하고 짧은 간격의 냉각채널 구조를 도입하여 반응채널의 열량을 충분히 제거할 수 있는 반응기설계에 대한 휴리스틱을 제안할 수 있었다. 이처럼 멀티채널 반응기의 모델을 설계하고 이로부터 적절한 변수를 선택해 그 경향성을 확인할 수 있는 방법을 통해 설계 단계에서부터 적절한 반응기 구조에 대한 제안을 하는데 도움을 줄 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1516-1521
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• 2004

Mixing in Y-channel micro mixer is analyzed through computational fluid dynamics. In the case of passive mixing, we investigate the effect of geometric parameters on the mixing efficiency, such as shape of throttling geometry and angle between two inlets. Mixing performance improves as two fluids join not just horizontally but both vertically and horizontally, and it also improves when channel follows throttling shapes. A numerical results substantiate the highly efficient mixing performance. It is highly beneficial to fabrication process since the proposed throttling geometry is simple, but allows high mixing ratio.