• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.99-102
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• 2006

Optimal flow-field design of bipolar-plates for a commercial class PEM(polymer electrolyte membrane) fuel cell stack was carried out on the basis of three-dimensional computational fluid dynamics(CFD) simulation. A three-dimensional CFD model originally developed by Shimpalee et al., has been utilized for performing large-scale simulation of a single fuel cell consisting of bipolar-plates gas diffusion layers, and a membrane-electrode-assembly(MEA). The CFD model is able to predict the current density, pressure drops, gas velocities, vapor and liquid water contents, temperature distributions, etc. inside a single fuel cell. Depending on simulation results from the CFD modeling of a PEM fuel cell, several flow-fields of bipolar-plates were designed and verified. The final design of the bipolar-plate has been chosen from the simulations and experimental tests and showed the best performance as expected from the simulation results under a normal operating condition. Thus, the CFD simulation approach to design the optimal flow-field of the bipolar-plates was successful. The final design was adopted as the best flow-field to build a commercial scale PEM fuel cell stack, the performance of which shows about 42% higher than that of the older bipolar-plate design.

• Current Photovoltaic Research
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• v.5 no.2
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• pp.63-67
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• 2017

Aluminum oxide ($Al_2O_3$) film deposited by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surface. The quality of passivation layer is important for high-efficiency silicon solar cell. double-layer structures have many advantages over single-layer materials. $Al_2O_3/SiN_X$ passivation stacks have been widely adopted for high- efficiency silicon solar cells. The first layer, $Al_2O_3$, passivates the surface, while $SiN_X$ acts as a hydrogen source that saturates silicon dangling bonds during annealing treatment. We explored the properties on passivation film of $Al_2O_3/SiN_X$ stack layer with changing the conditions. For the post annealing temperature, it was found that $500^{\circ}C$ is the most suitable temperature to improvement surface passivation.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.37-44
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• 2008

The global warming potential (GWP) of $CO_2$ refrigerant is 1/1300 times lower than that of R134a. Furthermore, the size and weight of the automotive heat pump system can decrease because $CO_2$ operates at high pressure with significantly higher discharge temperature and larger temperature change. The presented $CO_2$ heat pump system was designed for both cooling and heating in fuel cell vehicles. In this study, the performance characteristics of the heat pump system were analyzed for heating, and results for performance were provided for operating conditions when using recovered heat from the stack coolant. The performance of the heat pump system with heater core was compared with that of the conventional heating system with heater core and that of the heat pump system without heater core, and thus the heat pump system with heater core showed the best performance among the selected heating systems. On the other hand, the heating performance of two different types of coolant/air heat pump systems with heater core was compared each other at various coolant inlet temperatures. Furthermore, to use exhausted thermal energy through the radiator, experiments were carried out by changing the arrangement of a radiator and an outdoor evaporator, and quantified the heating effectiveness.

• The Journal of the Acoustical Society of Korea
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• v.14 no.6
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• pp.13-20
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• 1995

In this paper, the thermoacoustic refrigerating system was implemented and its operation was experimentally verified. The system is composed of several parts ,4 inch midrange speaker, speaker housing, chamber, stack housing, stack of plates, heat exchangers, thin pipe and cavity. The system is filled with He gas at 10 bar and contains T-type thermocouples and condenser microphone for measuring the temperature and pressure inside, respectively. In addition, cooling water is used for protecting speaker from thermal destruction and cooling down the hot heat exchanger. For the experimental verification of the implemented refigerating system, electrical impedance and resonance characteristics were measured. The results showed that it was most efficient to drive the system at 340 Hz. When operated at 340 Hz, $30^\circ{C}$ environments and 50 electical watts, the temperature of the cold region decreased by $16^\circ{C}$. The dissatisfaction mainly comes from the incomplete thermal insulation of the cold region. We also pointed out some guidelines to improve the performance for later study.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.39-46
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• 2006

The fuel cell is one of promising environment-friendly energy sources for the next generation. The bipolar plate is a major component of the PEM fuel cell stack, which takes a large portion of stack cost. In this study, as alternative materials for bipolar plate of PEM fuel cells, graphite composites were fabricated by compression molding. Graphite particles mixed with epoxy resin were used as the main substance to provide electric conductivity To achieve desired electrical properties, specimens made with different mixing ratio, processing pressure and temperature were tested. To increase mechanical strength, one or two layers of woven carbon fabric were added to the graphite and resin composite. Thus, the composite material was consisted of three phases: graphite particles, carbon fabric, and epoxy resin. By increasing mixing ratio of graphite, fabricated pressure and process temperature, the electric conductivity of the composite was improved. The results of tensile test showed that the tensile strength of the two-phase graphite composite was about 4MPa, and that of three-phase composite was increased to 57MPa. As surface properties, contact an91e and surface roughness were tested. Graphite composites showed contact angles higher than $90^{\circ}$, which mean low surface energy. The average surface roughness of the composite specimens was $0.96{\mu}m$.

• Biotechnology and Bioprocess Engineering:BBE
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• v.8 no.6
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• pp.360-367
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• 2003

Our research objectives are to determine under what conditions microalgal-based $CO_2$capture from flue gases is economically attractive. Specifically, our objective here was to select microalgae that are temperature, pH and flue gas tolerant. Microalgae were grown under five different temperatures, three different pH and five different flue gas mixtures besides 100% $CO_2$(gas concentrations that the cells were exposed to ranged 5.7-100% $CO_2$, 0-3504ppm SO$_2$, 0-328ppm NO, and 0-126ppm NO$_2$). Our results indicate that the microalgal strains tested exhibit a substantial ability to withstand a wide range of temperature (54 strains tested), pH (20 strains tested) and flue gas composition (24 strains tested) likely to be encountered in cultures used for carbon sequestration from smoke stack gases. Our results indicate that microalgal photosynthesis is a limited but viable strategy for $CO_2$capture from flue gases produced by stationary combustion sources.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.29-32
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• 2008

Testing was conducted to determine the performance of a residential fuel cell system when subjected to DSS and WSS operation, especially for start-up and shut-down characteristics. In terms of start-up time, it took about 70min to start output power generation and stably to reach 1kW at cold start. Measurement of the characteristics of heat and power generation were carried out at start-up and shut-down time. Fuel gas is used for heating both reformer and stack from start-up to the beginning of power generation. In terms of start-up and shut-down characteristics, it was important to control the reformer temperature precisely. The average output water temperature during the rated output operation(960W) was $63.2^{\circ}C$ constantly. The results of the investigation are being used to develop a new test protocols for residential fuel cell system.

• Journal of Magnetics
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• v.5 no.2
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• pp.50-54
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• 2000

NiMn-pinned spin valve films consisting of a layered glass/NiFe/Co/Cu/Co/NiFe/NiMn/Ta stack were made by do magnetron sputtering. After deposition, the structure was annealed in a series of cycles each including three hours at $220^\circ C, 2\times10^{-6}$ Torr, in a field of 350 Oe, to create an ordered antiferromagnetic structure in the NiMn layer and produce a strong unidirectional pinning field in the pinned magnetic layer, Optimum spin valve properties were obtained after seven annealing cycles, or 21 hours at $220^\circ C$, and were : MR ratio 1%, exchange coupling field 620 Oe, and coercivity of pinned layer 250 Oe. The exchange coupling field remained constant up to an operating temperature of $175^\circ C$, and the blocking temperature was about $380^\circ C$.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.223-228
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• 2001

The thermoacoustic refrigerator has not only considerable possibility but also commercial usability, because it has high reliability, lower vibration, no moving part, and can easily be constructed. In this study, The thermoacoustic refrigerator were constructed. The apparatus is capable of driving closed systems containing He or air at mean pressures ranging from 1-9.3 bar, at frequencies ranging from 100-1000Hz. The resonance characteristics of the thermoacoustic refrigerator were investigated for better performance, The resonance tube is 340.5mm in length. In case of using air as a coolant. Freezing frequency is 174Hz, In case of using He as a coolant Freezing frequency is 625Hz. Using He, The cold-part temperature of the heat exchanger fell to $-23.7^{\circ}C$ after 120 minutes in 70W.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.22-22
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• 2000

The discoveries of high temperature superconductors received great attention due to their high critical temperatures. These materials also exhibit extremely high critical magnetic fields and high critical current density at low temperature, high magnetic field. Thus, they are the most promising materials for superconducting magnets above 20 T. In this talk, progress in the development of HTS materials and insert coils at the National High Magnetic Field Laboratory will be reviewed. In 1999, a Bi-2212 stack of double pancakes generated 3 T in a 19 T background field. These results will be reviewed in terms of implications for future systems. Individual double pancakes of Bi-2223 have also been tested and their performance will also be discused. The present goal of a 57 system will be presented and the key technical requirements for larger, higher field systems will be addressed. It will be shown that in addition to increased critical current density, improved mechanical performance (stain resistanced) is necessary for high field systems. Furthemore, improvements in the conductor n-value will improve prospects for operational systems.