• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.283-287
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• 2007

KIER has been developing the anode-supported flat tubular solid oxide fuel cell unit bundle for the intermediate temperature($700{\sim}800^{\circ}C$) operation. Anode-supported flat tubular cells have Ni/YSZ cermet anode support, 8 moi.% $Y_2O_3$ stabilized $ZrO_2(YSZ)$ thin electrolyte, and cathode multi-layer composed of Sr-doped $LaSrMnO_3(LSM)$, LSM-YSZ composite, and $LaSrCoFeO_3(LSCF)$. The prepared anode-supported flat tubular cell was joined with ferritic stainless steel cap by induction brazing process. Current collection for the cathode was achieved by winding Ag wire and $La_{0.6}Sr_{0.4}CoO_3(LSCo)$ paste, while current collection for the anode was achieved by using Ni wire and felt. For making stack, the prepared anode-supported flat tubular cells with effective electrode area of $90\;cm^2$ connected in series with 12 unit bundles, in which unit bundle consists of two cells connected in parallel. The performance of unit bundle in 3% humidified $H_2$ and air at $800^{\circ}C$ shows maximum power density of $0.39\;W/cm^2$ (@ 0.7V). Through these experiments, we obtained basic technology of the anode-supported flat tubular cell and established the proprietary concept of the anode-supported flat tubular cell unit bundle.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.12-19
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• 2022

Cathode open-type PEMFC (Proton Exchange Membrane Fuel Cells) stacks, which are widely used in small transport-type PEMFC, have a problem with poor durability. Through the accelerated durability test of the 13-cell PEMFC stack, we tried to find the cause of the degradation of the stack and to contribute to the improvement of the durability of the cathode open stack. A hydrogen/air boundary is formed during start-up/shut-down (SU/SD) due to the structural problem of the cathode open stack in which the cathode is open to the atmosphere and it is difficult to maintain airtightness, thereby deteriorating the cathode. In this study, it was possible to evaluate the durability in a relatively short time by reducing the 54% of the initial performance by repeating SU/SD 1,800 times on the cathode open stack. After dismantling the stack, each cell was divided into two and the performance was analyzed. Overall, the anode outlet MEA, which facilitates air inflow, showed more severe electrode deterioration than the inlet MEA, confirming that the hydrogen/air boundary formation during SU/SD is the main cause of degradation.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.88.1-88.1
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• 2011

SOFC는 사용되는 셀의 디자인에 따라 튜브형, 평판형으로 구분되어진다. 평판형의 경우에는 전해질 지지형(ESC), Anode 지지형(ASC) 및 금속 지지형(MSC)로 크게 나눌 수 있다. SOFC 스택은 이와 같은 셀과 밀봉재, 집전체, 분리판의 구성요소를 여러 장으로 적층하여 이루어진다. SOFC 발전시스템은 SOFC 스택과 EBOP, MBOP로 구성되는데, SOFC 발전시스템의 상용화를 위해 선행되어야 할 것은 스택의 안정적 출력 및 신뢰성 확보이다. 즉, 셀, 밀봉재, 분리판 및 집전체로 대변되는 구성요소들이 스택에 장착되었을 때 그 기능을 최대한 발휘하면서도 점진적 또는 급격한 품질저하가 발생되지 말아야 한다. 특히, 밀봉재의 경우 SOFC에 사용되는 연료와 공기의 혼합(Cross-over)을 방지하는 중요한 기능을 담당하고 있으며 여러 장 적층된 분리판의 전기적 단락을 방지해야 한다. 또한 SOFC의 특성상 $700^{\circ}C$ 이상의 고온에서 다른 구성요소와 화학적 반응이 없어야하고 열싸이클(Thermal cycle)을 견딜 수 있도록 충분한 기계적 강도가 보장되어야 하는 등 요구되는 품질기준이 엄격하다. SOFC의 밀봉재는 접합형(Brazing), 압착형(Compressive), 용융-고정형(Glass-ceramic)이 대표적으로 적용되고 있다. 이 중에서 Brazing 물질과 방법은 현재 활발히 연구가 수행 중에 있지만 범용적으로 사용되고 있지는 않은 상태이고 Compressive 밀봉재와 Glass-ceramic 밀봉재가 대면적 SOFC 스택에 사용되어 적용 가능성을 평가받고 있다. 본 연구에서는 SOFC 구성요소의 국산화를 추진하는 지경부과제의 결과물 중 (주)써모텍에서 개발한 Glass-ceramic 밀봉재(RC1) 단품에 대한 특성평가와 실제 단전지 평가를 통해 SOFC 스택 적용 가능성을 평가하였다. 밀봉재 단품에 대한 특성평가는 용융특성, 상분석, 열팽창계수 등의 물리적, 화학적 평가 외에 가스 누설 정도를 평가하는 기밀도 평가와 SOFC의 작동 온도인 $700^{\circ}C$와 상온 분위기를 주기적으로 인가하는 Thermal cycle 특성을 평가하였다. 셀을 한 장 사용하는 단전지(Unit cell) 평가는 RIST에서 자체 제작한 $100{\times}100mm^2$ 평판형 ASC 셀을 사용하여 수행하였으며, 밀봉재는 Dispensing 공정을 통해 구성되었다.

• Korean Chemical Engineering Research
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• v.51 no.3
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• pp.370-375
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• 2013

We analyze the effects of CO poisoning and air bleeding on the performance of a PEM (polymer electrolyte membrane) fuel cell stack fabricated using commercial MEA (membrane electrode assembly). Dynamic response data from the experiments on the performance of a stack are identified by obtaining steady-state gains and time-constants of the first-order system model expressed as a first-order differential equation. It is found that the cell voltage of the stack decreases by 1.3-1.6 mV as the CO concentration rises by 1 ppm. The time elapsed to reach a new steady state after a change in the CO concentration is shortened as the magnitude of the change in the CO concentration increases. In general, the steady-state gain becomes bigger and the time-constant gets smaller with increasing the air concentration (air-bleeding level) in the reformate gas to restore the cell voltage. However, it is possible to recover 87%-96% of the original cell voltages, which are measured with free of CO, within 1-30 min by introducing the bleed air as much as 1% of the reformate gas into the stack.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.512-512
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• 2012

최근 저온 대기압 플라즈마 장치의 개발로 대기 및 수질 환경, 바이오 메디컬분야로의 응용 연구가 활발히 진행되어 공기 중 플라즈마의 살균 및 정화효과에 대한 많은 결과가 발표되어 왔다. 본 연구는 면방전 구조의 DBD플라즈마 소스를 제작하여 He과 Ar 기체를 유입하여 미생물인 E.Coli의 변화를 관찰하였다. 면방전 구조의 DBD플라즈마 소스는 1.8 mm 두께의 유리기판위에 포토리소그라피 공정으로 미소전극을 형성하여 고밀도의 방전 셀을 형성하였으며 방전시 발생하는 열 효과를 제어하기 위하여 냉각장치를 제작하여 장착했다. 또한 유리기판과 포토 리소그라피 공정은 방전영역에 제한없이 다양한 크기의 소스제작이 가능하다. 셀 피치가 $400{\mu}m$이며 $cm^2$ 당 200여개의 방전 셀로 구성되어 있어서 기존 메쉬타입의 DBD플라즈마 장치에 비해 균일하게 플라즈마를 조사할 수 있으며 플라즈마 제트 장치에 비해서는 넓은 면적을 동시에 조사할 수 있게 되었다. Ar 과 He기체를 3 L/min의 유량으로 방전공간에 유입하면서 1kV의 구동전압으로 플라즈마를 발생 하였으며, 플라즈마의 조사시간을 20 s, 40 s, 60 s 간격으로 변화를 주어 E.Coli의 변화를 관찰하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.115-124
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• 2002

The optimum design of auto-catalyst needs a good compromise between the pressure drop and flow distribution in the monolith. One of the effective methods to achieve this goal is to use the concept of radially variable cell density. However, there has been no study of evaluating the usefulness of this method on light-off catalyst. We have computationally investigated the effectiveness of variable cell density technique applied to the light-off catalyst using a three-dimensional integrated CFD model. in which transient chemical reacting calculations are involved. Computed results show that variable cell density technique can reduce the accumulated emissions of CO and HC during the early 100sec of FTP cycle by 86.78 and 80.87%, respectively, The effect of air-gap between the monoliths has been also examined. It is found that air-gap has a beneficial effect on reducing pressure drop and cold-start emissions.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.83.1-83.1
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• 2011

고체산화물 연료전지는 전해질의 양쪽에 cathode층과 anode층으로 구성되어 있다. 이러한 셀을 제작하기 위한 구성소재 코팅법으로는 EVD, CVD, sputter등의 기상공정과 screen printing, tape casting, dip coating등의 습식공정이 있다. 이중 현재 가장 널리 사용되고 있는 screen printing법은 코팅기판의 크기와 형태에 제한을 받아 원통형, 평관형에는 적용이 어렵다. 이러한 문제점을 해결하기 위해 본 연구에서는 electrolyte 지지체 위에 전사법을 통해 연료극(NiO-YSZ), 공기극(LSCF-GDC) 코팅층의 두께 및 형상을 제어할 수 있었으며 button cell을 제작하여 실제 SOFC에 적용이 가능함을 확인하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.8
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• pp.755-762
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• 2000

Natural convection of air in a horizontal annulus with the inner cylinder cooled by the application of a constant heat flux and the isothermally heated outer cylinder is considered. The bifurcation phenomenon of flow patterns and the heat transfer characteristics are numerically investigated. The zero initial condition induces a unicellular flow in a half annulus. A bicellular flow consisting of two counter-rotating eddies in a half annulus can be obtained above a certain critical Rayleigh number. A transition from the bicellular to the unicellular flow occurs with a decrease in Rayleigh number. Hysteresis phenomena have not been observed. In the regime of dual flows, the overall Nusselt number of the bicellular flow is greater than that of the unicellular flow.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.638-644
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• 2019

In this study, the fluid flow and heat transfer characteristics within sandwich panels are investigated using computational fluid dynamics. Within the sandwich panels having periodic cellular cores, air can freely move inside the core section so that the structure is able to perform multi-functional roles such as simultaneous load bearing and heat dissipation. Thus, there needs to examine the thermal and flow analysis with respect to design variables and various conditions. In this regard, ANSYS Fluent was utilized to explore the flow and heat transfer within the pyramidal truss sandwich structures by varying the truss angle and inlet velocity. Without the entry effect in the first unitcell, the constant rate of pressure and the constant rate of Nusselt number was observed. As a result, it was demonstrated that Nusselt number increases and friction factor decreases as the inlet velocity increases. Moreover, the rate of Nusselt number and friction factor was appreciable in the range of V=1-5m/s due to the transition from laminar to turbulent flow. Regarding the effect of design variable, the variation of truss angle did not significantly influence the characteristics.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.625-632
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• 2012

The objective of this paper is to demonstrate the cathode channel flooding effects at different stoichiometries in proton exchange membrane (PEM) fuel cells by using visualization techniques. The phenomena of liquid water formation and removal caused by current variations were also examined experimentally. Tests were conducted at cathode stoichiometries of 1.5 and 2.0, and the anode stoichiometry was fixed at 1.5. It is found that at an air-side stoichiometry of 2.0, liquid water begins to form and the flooding occurs faster than at an air-side stoichiometry of 1.5. Also, when the air-side stoichiometry of 1.5 is maintained, the dry-out phenomena is observed in the dry-out area 7.8 A following the field of flooding. Thus, a stoichiometry of 1.5 produced better performance in terms of membrane electrode assembly (MEA) durability and hydrogen ion conductivity than did a stoichiometry of 2.0, in which dry-out occurs beyond 8A.