• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• 대한기계학회논문집B
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• 제33권4호
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• pp.288-297
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• 2009

A serpentine channel geometry often used in a fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from the intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with high aspect ratio of active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compressive forces. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds that of dropwise condensation in cathode channels.

• 전기화학회지
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• 제15권2호
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• pp.74-82
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• 2012

고분자전해질 연료전지의 성능은 매우 복잡한 물리 현상들에 의해 변화하게 된다. 반응면적이 25 $cm^2$인 5-pass, 4-turn 사행성 유동유로의 립 부분에 보조유동유로를 가지는 형상에 대하여 물관리 측면에서의 연료전지 성능을 수치해석을 통해 비교하였다. 보조유동유로를 추가함에 따라 촉매층 공급 대류의 유동 방향이 변경되어 유로 내부의 물 배출 특성을 향상시키는 결과를 나타내었다. 또한 입구에서의 공급기체를 보조유동유로로 분산시킴에 따라 입구에서의 전류 밀도는 낮아지며 보조유동유로로 이동하는 공급기체들은 주 유동유로의 내에서의 체류시간보다 길어져서 전체적인 전류밀도 분포가 균일해지는 것을 확인하였다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.147-151
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• 2007

A serpentine channel geometry often used in a polymer electrolyte membrane fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with relatively high aspect ratio active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compression conditions. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds to that of dropwise condensation in cathode channels.

• 한국수소및신에너지학회논문집
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• 제23권4호
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• pp.293-299
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• 2012

The serpentine flow channel is widely used in polymer electrolyte membrane fuel cells (PEMFCs) to prevent flooding phenomena because it effectively removes liquid water in the flow channel. The pressure drop between inlet and outlet increases as compared with straight channels due to minor losses associated with the corners of the turning configurations. This results in a strong pressure gradient between adjacent channels in specific regions, where some amount of reactant gas can be delivered to catalyst layers by convection through a gas diffusion layer (GDL). The enhancement of the convective flow in the GDL, so-called bypass flow, affects fuel cell performance since the bypass flow influences the reactant transport and thus its concentration over the active area. In the present paper, for the bipolar plate design, a simple analytic model has been proposed to predict the bypass flow in the serpentine type flow channels and validated with three-dimensional numerical simulation results.

• 전기화학회지
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• 제10권4호
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• pp.245-251
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• 2007

주어진 연료전지면적에서 반응면적이 넓을수록 성능이 향상되는 연료전지는 좁은 폭의 채널을 여러 개 존재하게 하는 구조를 선호하지만 채널 폭이 좁아질수록 압력이 커지는 문제가 고려되어져야 한다. 그러나 현재 채널 구조에 따른 압력에 대한 연구는 많이 진행되어져 왔지만 대부분 반응을 고려하지 않았으며, 반응을 고려한 경우에 어떤 경향을 나타내는지 알아보는 것이 연료전지 유로설계에 있어 매우 중요하다. 본 논문에서 화학반응을 고려한 평행류, 90도 밴드형, serpentine 세가지 종류의 유로채널를 가진 연료전지를 수치 해석하여 반응을 고려하지 않은 경우와 마찰계수(fRe), 속도, 압력강하를 비교하여 본 결과 parallel과 bend 형태의 채널은 반응을 고려한 경우 반응에 의한 밀도의 감소에 따라 근소하게 감소한 것을 알 수 있었다. 그러나 serpentine채널은 다공성매체인 확산층을 통해 인접한 채널로 가스가 이동하는 bypass flow 영향에 의하여 상대적으로 낮은 압력강하를 나타내는 것을 알 수 있었다.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1201-1208
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• 2002

A numerical flow-field analysis is performed to investigate flow configurations in the anode, cathode and cooling channels on the bipolar plates of a proton exchange membrane fuel cell (PEMFC). Continuous open-faced flow channels are formed on the bipolar plate surface to supply hydrogen, air and water. In this analysis, two types of channel pattern are considered: serpentine and spiral. The averaged pressure distribution and velocity profiles of the hydrogen, air and water channels are calculated by two-dimensional flow-field analysis. The equations for the conservation of mass and momentum in the two-dimensional fluid flow analysis are slightly modified to include the characteristics of the PEMFC. The analysis results indicate that the serpentine flow-fields are locally unstable (because two channels are cross at right angles). The spiral flow-fields has more stable than the serpentine, due to rotational fluid-flow inertia forces. From this study, the spiral channel pattern is suggested for a channel pattern of the bipolar plate of the PEMFC to obtain better performance.

• 한국수소및신에너지학회논문집
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• 제26권6호
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• pp.554-559
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• 2015

Single cell of PEMFC (polymer electrolyte membrane fuel cell) is composed of bipolar plates, gasket, GDL and the MEA. Bipolar plate's function is the collecting electricity, helping oxygen/hydrogen gas diffuse evenly and draining the water and heat. In this work, we have conducted experiments to low contact resistance and improve the performance of a $25cm^2$ single cell by using metal forms. We have following experimental cases: 1) Conventional graphite serpentine channel bipolar plate; 2) Channel-less bipolar plate with nickel(Ni) based metal foam which coated by various materials. We focused the difference in contact resistance and performance of the single cell with metal foam depending on various coating materials. The experimental results show the similar performance of single cells between with serpentine channel bipolar plates and with channel-less bipolar plate using metal foams. In addition, single cell with metal foam shows potential to higher performance than conventional channel.

• 대한기계학회논문집A
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• 제30권10호
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• pp.1261-1268
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• 2006

This paper reports low-cost microreactor $(10{\mu}{\ell})$ biochip for the DNA PCR (polymerase chain reaction). The microbiochip $(20mm{\times}28mm)$ is a hybrid type which is composed of PDMS (polydimethylsiloxane) layer with serpentine micochannel $(360{\mu}m{\times}100{\mu}m)$ chamber and glass substrate integrated with microheater and thermal microsensor. Undesirable bubble is usually created during sample loading to PMDS-based microchip because of hydrophobic chip surface. Created bubbles interrupt stable biochemical reaction. We designed improved microreactor chamber using microfluidic simulation. The designed reactor has a coner-rounded serpentine channel architecture, which enables stable injection into hydrophobic surface using micropipette only. Reactor temperature needed to PCR reaction is controlled within ${\pm}0.5^{\circ}C$ by PID controller of LabVIEW software. It is experimentally confirmed that SRY gene PCR by the fabricated microreactor chip is performed for less than 54 min.

• 한국산학기술학회논문지
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• 제22권3호
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• pp.415-421
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• 2021

본 연구는 절연 게이트 양극성 트랜지스터 모듈의 히트 싱크의 유로의 형상으로써 직선 유로, 한 번 꺾인 형태의 유로, 두 번 꺾인 형태의 유로를 적용하여, 유로의 형상에 따른 방열 성능을 분석하였다. 각 유로 형상에서 운전 조건에 대한 영향 또한 분석하기 위하여 냉각수의 유량과 공급 온도를 추가적으로 제어하며 분석을 진행하였다. 본 연구는 유동 해석을 통하여 이루어 졌으며, 상용 소프트웨어인 ANSYS Fluent를 사용하였다. 직선 유로보다 꺾인 형태를 갖는 유로의 방열량이 같은 운전 조건에서 최대 8.0 % 수준 개선되었으며, 개선 정도는 냉각수의 공급 온도와는 무관하였고, 냉각수의 유량이 많아질수록 개선 정도가 2.0 %에서 8.0 %까지 증가하였다. 그러나 두 번 꺾인 유로는 한 번 꺾인 유로와 비슷한 수준의 방열 성능을 보였고, 기생 손실에 영향을 주는 압력 강하량은 2.48~2.55배 수준으로 증가하는 결과를 보여, 방열 효율이 낮아지는 것을 확인 하였다. 이를 단위 압력 강하량 당 방열량으로 계산하여 비교하였으며, 직선 유로를 갖는 히트 싱크에서 그 값이 가장 높은 것을 확인하였다.