• Journal of the Korean Electrochemical Society
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• v.9 no.3
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• pp.118-123
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• 2006

Degradation of polymer electrolyte membrane fuel cell (PEMFC) that is facilitated by on/off cycles is one of the most important issues for commercialization of fuel cell vehicles. When a PEMFC stack is shut down, residual hydrogen and induce high voltage equivalent to open circuit voltage to the cathode side that might cause sintering of Pt catalyst and facilitate formation of hydrogen peroxide at the anode side that might decompose $Nafionc\'{A}$ membrane. In this study, degradation of PEMFC exposed to repetitive on/off cycles was investigated by measuring i-V characteristics, ac impedance, cyclic voltammograms, gas leak, cross-sectional SEM images, and TEM images. To prevent degradation of PEMFC caused by the residual gases, hydrogen was removed from anode gas channel by gas-purging and by using a dummy resistance, that were found to be a very effective method.

• Journal of the korean Society of Automotive Engineers
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• v.26 no.3
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• pp.21-25
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• 2004

연료전지의 종류는 전해질의 종류로 나누는 것이 일반적으로, 운전 및 정지를 반복하는 자동차용에는 작동 온도까지 상변화가 없는 고체 전해질이 유리하다고 할 수 있는데 프로톤 교환막과 고체산화물이 바로 그것이다. 프로톤 교환막 연료전지는 다른 종류의 연료전지 보다 작동온도가 8$0^{\circ}C$ 내외로 낮고, 단위전지 면출력밀도가 커서 현재 자동차용으로 가장 많이 개발되고 있다. 그 결과 자동차 구동에 적당한 80㎾급의 연료전지 스택이 자동차에 장착될 수 있는 크기로 개발되어 적용되고 있다. (중략)

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.659-665
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• 1995

액체금속로는 기존의 가압경수로와는 달리 55$0^{\circ}C$ 정도의 고온에서 운전이 되므로 고온 열응력이 중요한 문제로 대두되며 따라서 고은에서의 크립(Creep) 변형, 반복되는 기동과 정지 등으로 인한 되풀이 소성변형, 라체팅(Ratchetting), 크립과 소성의 상호작용 및 크립과 피로의 상호작용 등의 평가에 대한 기술 확립과 고온구조물에 대한 우리의 독자적인 설계방법을 개발하는 것이 필요하다 본 연구에서는 범용 유한요소해석코드인 ABAQUS의 축대칭 요소를 이용해서 액체 금속로 원자로용기와 이에 부착된 열소매(Thermal sleeve)를 Y-형태의 구조물로 모델링하여 반복되는 열천이하중에 대한 비탄성 구조해석을 수행하고 크립효과에 대한 영향을 분석하였다. 해석결과 액체금속로와 같은 고온구조물에 대하여 반복 열천이 하중과 고온 지속시간이 유발하는 크립효과가 크게 나타남을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.157-164
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• 2017

A parallel slide gate valve (PSGV) is located between the heat recovery steam generator (HRSG) and the steam turbine in a combined cycle power plant (CCPP). It is used to control the flow of steam and runs with repetitive operations such as startups, load changes, and shutdowns during its operation period. Therefore, it is necessary to evaluate the fatigue damage and the structural integrity under a large compressive thermal stress due to the temperature difference through the valve wall thickness during the startup operations. In this paper, the thermal-structural analysis and the fatigue life evaluation of a 16-inch PSGV, which is installed on the HP steam line, is performed according to the fatigue life assessment method described in the ASME B&PVC VIII-2; the method uses the equivalent stress from the elastic stress analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.5
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• pp.549-554
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• 2011

Recently, technical advances have been made in high efficiency gas turbine power plants. In domestic gas turbine facilities, the material properties of the blade and vane are degraded by the daily start-stop operations arising from the thermo mechanical cycle. We surveyed the time dependent degradation of the HP blade and vane to gather basic data for life assessment and damage analysis. The EOH(equivalent operating hours) of the blades were 23,686, 27,909, and 52,859 and the EOH of the vanes were 28,714 and 52,859, respectively. With increased operating hours, the shape of the primary ${\gamma}$' precipitate transformed from cubic to spherical, and its average size also increased. The leading edge area of the blades and the center of the vanes had the worst morphology, and this tendency agrees with the microhardness results. The thickness of the thermally grown oxide at the outer surface of the bond coat increased with increased operating hours.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.679-683
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• 2016

Boilers of large-sized coal-fired power plants are being operated under very poor conditions such as continuous operation or repeating of start-up and shutdown for a stable supply of electricity. Thus periodic inspection and maintenance are required to ensure reliability of operation. The loads of existing scaffolding systems for the maintenance of boilers are concentrated in the lower parts structurally, which may cause a serial collapse of the overall scaffolding system when there are problems in some members. Therefore, in this study, a safe furnace scaffolding system is developed by dispersing the loads in the upper part, as well as minimizing the hazards of serial collapsing. In addition, for cases where the direct installation of furnace scaffolding is challenging owing to the structure of the boiler tube, a lifting system for the installation of furnace scaffolding is developed so that furnace scaffolding can be supported to secure the integrity of the power generating facility.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.1
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• pp.31-39
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• 2005

Direct methanol fuel cell (DMFC) is considered as a candidate for portable power sources, that could overcome the disadvantages of lithium battery. But in order to attain commercial viability the long term stability of the DMFC should be achieved. Understanding the long-term behavior of membrane-electrode assembly (MEA) is a prerequisite to this purpose and the optimization of the MEA is also needed. In this study we have investigated the changes in performance and electrochemical properties of the MEA during extended operation and the effects of heat treatment of MEA on the long-term performance. The MEAs have been treated in an autoclave with saturated water vapor at 120$^{\circ}C$, vacuum oven at 140$^{\circ}C$ and boiling in organic solvents. The autoclaved MEA was found to be have the best long term performance. The on-off operation mode also increased the performance probably due to effective removal of products from the electrodes. Physical and electrochemical analyses using a scanning electron microscope, impedance analyser and half-cell technique have been done to characterize the MEAs.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.908-914
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• 2017

In this study, we developed a system that automatically removes the scale in the piping by using electrolysis principle in order to solve the cooling performance of the refrigeration and air conditioning system by acting as heat resistance in the heat transfer process by forming the scale in the heat exchanger for refrigeration air conditioning. We want to check the performance through experiments. Therefore, by circulating the treated water using the principle of electrolysis without stopping the system, Ca, Mg and $SiO_2$ are precipitated in the form of solids and discharged to the outside of the pipe system, thereby preventing scale formation in the pipe and removing the scale. Thereby maintaining the heat transfer performance of the pipe. As a result of the experiment, the heat transfer rate of the scaled pipe was 86.66% when the heat transfer rate of the new pipe was 100, and the heat transfer rate was recovered to 90.5% when the scaled pipe was operated for 1 month. The heat transfer rate recovered to 97.86% when driving for two months and to 98.72% for three months. It was confirmed that the scaling effect of the scale formed in the piping was understood in a relatively short experiment period, and the heat transfer performance was also influenced.