• 한국환경과학회지
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• 제14권9호
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• pp.851-860
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• 2005

In order to how well predict ISCST3(lndustrial Source Complex Short Term version 3) model dispersion of air pollutant at point source, sensitivity was analysed necessary parameters change. ISCST3 model is Gaussian plume model. Model calculation was performed with change of the wind speed, atmospheric stability and mixing height while the wind direction and ambient temperature are fixed. Fixed factors are wind direction as the south wind(l80") and temperature as 298 K(25 "C). Model's sensitivity is analyzed as wind speed, atmospheric stability and mixing height change. Data of stack are input by inner diameter of 2m, stack height of 30m, emission temperature of 40 "C, outlet velocity of 10m/s. On the whole, main factor which affects in atmospheric dispersion is wind speed and atmospheric stability at ISCST3 model. However it is effect of atmospheric stability rather than effect of distance downwind. Factor that exert big influence in determining point of maximum concentration is wind speed. Meanwhile, influence of mixing height is a little or almost not.

• JSTS:Journal of Semiconductor Technology and Science
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• 제7권2호
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• pp.120-131
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• 2007

A comprehensive short channel analytical model has been proposed for High Electron Mobility Transistor (HEMT) to obtain higher cut-off frequency maintaining the reliability of the device. The model has been proposed to consider generalized doping variation in the directions perpendicular to and along the channel. The effect of field plates and different gate-insulator geometry (T-gate, etc) have been considered by dividing the area between gate and the high band gap semiconductor into different regions along the channel having different insulator and metal combinations of different thicknesses and work function with the possibility that metal is in direct contact with the high band gap semiconductor. The variation obtained by gate-insulator geometry and field plates in the field and channel potential can be produced by varying doping concentration, metal work-function and gate-stack structures along the channel. The results so obtained for normal device structure have been compared with previous proposed model and numerical method (finite difference method) to prove the validity of the model.

• 설비공학논문집
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• 제26권7호
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• pp.343-350
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• 2014

Regardless of the building design scenarios, evaluation of high-rise buildings required to have smoke-proof enclosures that are provided with a smoke management system. The goal of the smoke management system design is to make sure the pressure differentials at every story within the building fall within the allowable pressure range. If the minimum design pressure is not met, smoke may enter the stair. If the provided pressure is too great, it becomes difficult for occupants to open the doors, while attempting to egress. Ensuring that the pressure differential between the vestibule and the floor is within the prescribed range becomes challenging, due to natural effects on the building, such as the stack effect. In this research, smokeproof enclosure design scenarios were evaluated; and as a result, separation levels for compartmentation were deduced, in the balancing of pressurized-vestibule smoke control systems.

• Journal of Magnetics
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• 제10권2호
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• pp.48-51
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• 2005

The spin transfer induced magnetization switching has been reported to occur in magnetic multilayer structures whose scope usually consists of one stack of ferromagnetic / non-ferromagnetic / ferromagnetic (F / N / F) materials. In this work, it is shown that: 1) Copper used as a buffer layer between the free Co and the Au cap-layer can clearly increase the probability to get the spin transfer induced magnetization switching in a simple spin valve Co 11 / Cu 6/ Co 2 (nm); 2) Furthermore, when Ruthenium is simultaneously applied as a buffer layer on the Si-substrate, the critical switching currents can be reduced by $30\%$, and the absolute resistance change delta R $[{\Delta}R]$ of that stack can be enlarged by $35\%$. The enhancement of the spin transfer induced magnetization switching can be ascribed to a lower local stress in the thin Co layer caused by a better lattice match between Co and Cu and the smoothening effect of Ru on the thick Co layer.

• 한국화재소방학회논문지
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• 제25권6호
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• pp.178-183
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• 2011

초고층 건물의 승강기는 혹한기에 연돌효과에 의한 차압 때문에 고층부의 승강기 문틈에서 소음을 유발하고, 1층에서 승강기 문 개폐에 영향을 줄 정도의 강한 압력이 발생하며, 화재시에는 건물 내에 연기를 전파시키는 주된 구동력이 된다. 또한 승강기를 피난용으로 사용하기 위해서도 연돌효과는 반드시 극복되어야 할 과제이다. 이 논문에서는 연돌효과가 고층건물의 승강기 승강로에 미치는 부정적 영향을 줄이기 위해 승강로를 가압하는 방식을 검토하였다. 승강로와 거실 사이를 균압화하고 승강로를 급기 가압하는 조건으로 시뮬레이션 함으로써 NFPA 92A와 IBC 2012에서 요구하는 조건에 근접하는 결과를 얻었다.

• 한국분무공학회지
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• 제22권2호
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• pp.69-79
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• 2017

When designing a redox flow battery system, compression of battery stack is required to prevent leakage of electrolyte and to reduce contact resistance between cell components. In addition, stack compression leads to deformation of the porous carbon electrode, which results in lower porosity and smaller cross-sectional area for electrolyte flow. In this paper, we investigate the effects of electrode compression on the cell performance by applying multi-dimensional, transient model of all-vanadium redox flow battery (VRFB). Simulation result reveals that large compression leads to greater pressure drop throughout the electrodes, which requires large pumping power to circulate electrolyte while lowered ohmic resistance results in better power capability of the battery. Also, cell compression results in imbalance between anolyte and catholyte and convective crossover of vanadium ions through the separator due to large pressure difference between negative and positive electrodes. Although it is predicted that the battery power is quickly improved due to the reduced ohmic resistance, the capacity decay of the battery is accelerated in the long term operation when the battery cell is compressed. Therefore, it is important to optimize the battery performance by taking trade-off between power and capacity when designing VRFB system.

• 설비공학논문집
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• 제23권2호
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• pp.153-163
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• 2011

Energy efficiency and indoor air quality have become main issue to develop healthy and sustainable building in these days. As an effort to reduce the energy consumption in multi-residential building, many attempts as like passive design strategies and renewable energy as well as active control method are tried. However, underground parking lot in multi-residential building seldom adopt the sustainable strategies and only mechanical system is installed as usual. Moreover, the mechanical system installed in underground parking lot is rarely operated due to the electric demand for operation after completion. In this study, as an energy efficient measure, natural ventilation system using stack effect as a driving force for underground parking lot will be proposed and the performance of the suggested system will be analyzed by simulation method.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.34-40
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• 2015

A stack in the proton exchange membrane fuel cell (PEMFC) consists of bipolar plates, a membrane electrode assembly, a gas diffusion layer, a collector and end plates. High current density is usually obtainable partially from uniform temperature distribution in the fuel cell. A size optimization method considering the thermal expansion effect of stacked plates was developed on the basis of finite element analyses. The thermal stresses in end, bipolar, and cooling plates were calculated based on temperature distribution obtained from thermal analyses. Finally, the optimization method was applied and optimum thicknesses of the three plates were calculated considering both fastening bolt tension and thermal expansion of each unit cell (72 cells, 5kW). The optimum design considering both thermal and mechanical loads increases the thickness of an end plate by 0.64-0.83% the case considering only mechanical load. The effect can be enlarged if the number of stack increases as in an automotive application to 200-300 stacks.

• 한국인터넷방송통신학회논문지
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• 제21권3호
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• pp.51-57
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• 2021

본 논문에서는 샤논 정리(1948)의 동기가 되는 아인슈타인 특수상대성이론(1905)과 베르누이 유체역학(1738)의 상관성을 AB=A/A=I Dimension 관점에서 유도했고 샤논 정리 채널코드를 시뮬레이션했다. 베르누이 유체역학 ΔP=pgh를 한라산 화산 Magma 폭발식으로 적용했을 때 Dimension과 높이가 실측치와 일치했다. 아인슈타인 특수상대성이론과 샤논의 정보이론, 그리고 유체역학의 연돌효과(Stack Effect) 이론의 관계를 분석해 보고 화산 폭발의 관계를 수학적으로 증명했다. 아인슈타인, 베르누이의 에너지보존과 질량보존은 샤논 정리에서는 대역폭과 power의 효율면과 같았다.

• 전기화학회지
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• 제10권4호
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• pp.301-305
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• 2007

연료전지 운전 중에 스택(stack) 분리판 접착부위나 다른 경로로 부동액이 누설될 경우에는 화학적 반응에 영향을 주어 성능의 저하가 발생할 수 있다. 본 연구에서는 부동액이 누설되었을 경우의 성능 거동을 관찰하는 실험을 수행하였다. $400mA/cm^2$ 전류밀도 조건에서 마이크로 펌프를 이용하여 부동액을 주입하였으며 상대습도 100%/100%와 수소와 공기의 양론비는 1.5/2.0으로 고정하여 실험을 수행하였다. 3 cell stack을 이용하여 부동액을 주입한 후 정전류 회복 실험을 수행한 결과 cathode측에 부동액을 주입하였을 경우에는 성능이 회복되었고 anode측에 부동액을 주입하였을 경우에는 성능이 회복되기 어려운 것으로 나타났다. Anode측이 회복되지 못하는 이유로는 ethylene glycol의 산화반응에서 발생하는 불순물에 의한 피독 현상과 GDL과 3상 계면에 ethylene glycol이 물리적으로 흡착하였을 경우 반응에 필요한 연료 공급의 방해로 인한 성능 저하를 예상할 수 있다. 성능 저하에 영향을 주는 두 가지 변수를 확인하는 실험을 수행하였다. 회복 실험은 anode측에 water pump를 이용하여 질소 기체와 물을 동시에 공급하는 방법으로 실험을 수행하였고, 1시간 간격으로 성능 회복 유무를 확인하였다. 성능 평가는 polarization curve, cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS)를 사용하였으며, 정량분석은 gas chromatography를 이용하여 분석하였다. 부동액 주입 후 성능은 크게 저하되었고 정전류 회복 실험에서도 성능 회복은 미미하게 나타났다. 이 후 물 주입회복 실험을 수행하였고 회복 실험을 수행한 2시간 이후에는 93% 이상의 회복을 관찰할 수 있었다.