• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.751-760
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• 2014

The unmanned underwater vehicle(UUV) requires the highly dense energy source because of its limited space. Especially, for the UUV designed for long-term operation, it should be reviewed first whether it is possible to install the energy source against required total power. Therefore, this study identifies whether it is possible to install the energy source for the energy requirement of the UUV. And fuel and oxidizer requirement for the fuel cell system are calculated to determine its location and layout inside of the vehicle. Finally, we design the closed type 1kW polymer-electrolytic fuel cell system and check the applicability to underwater operations with UUV.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.69-75
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• 2006

The microbubbles were used in various fields, such as turbulent control, drag reduction, material science and life science. The X-ray PTV using X-ray micro-imaging technique was employed to mea-sure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}$=2.7mm) were tested. Due to the different refractive indices of water and air, phase contrast X-ray images clearly show the exact size and shape of over-lapped microbubbles. In all of the working fluids tested (deionized water, tap water, 0.01 and 0.10M NaCl solutions), the measured terminal velocity of the microbubbles rising through the solution was proportional to the square of the bubble diameter. The rising velocity was increased with increasing mole concentration. The microbubble can be useful as contrast agent or tracer in life science and biology. The X-ray PTV technique should be able to extract useful information on the behavior of various bio/microscale fluid flows that are not amenable to analysis using conventional methods.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.372-372
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• 2011

염료 감응형 태양전지는 상,하판 투명전극(TCO), 나노입자의 다공질 TiO2, 염료 고분자 층으로 구성된 광전극과 투명전극 및 백금(Pt) 박막으로 구성된 상대전극 그리고 두 전극 사이를 산화 환원용 전해질 용액으로 채우고 있는 구조이다. 이 구조에서 투명전극(TCO)은 재료비의 많은 부분을 차지하므로 제작비용 절감을 위한 TCO-less에 관한 연구가 활발히 진행 중이다. 본 연구에서는 TCO-less 염료 감응형 태양전지 제작을 위해 이중층 Ti 전극 구조를 제안하였다. 제작과정은 광조사 부분을 확보한 유리기판에 e-beam 증착법을 이용해 Ti 전극을 증착시킨 후 TiO2를 Ti전극과 일부 중첩하여 인쇄하고 그 위에 두 번째 Ti전극을 제작한다. 이중층 Ti전극 구조는 SEM, EIS 등의 분석장비를 사용하였고 기존 FTO 구조에 비해 단락전류밀도, 에너지 변환효율은 감소하였으나 직렬 내부저항이 약 27% 감소하여 fill factor가 28% 향상된 결과를 얻을 수 있었다.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.4
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1292-1295
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• 2006

Three kinds of electrolyte membranes were prepared by impregnating filter papers with one of the electrolyte solutions fur primary manganese battery ($NH_4Cl$, $ZnCl_2$, and alkaline types) and hygroscopic agent ($CaBr_2$ or $CaCl_2$), respectively. The thickness of them was $250{\sim}300{\mu}m$, and they were very flexible. The electrochemical characteristics greatly depended on the hygroscopic agent to supply water to the cell. The electrolyte membrane containing $CaCl_2$ showed the highest ionic conductivity and the largest discharge capacity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.218-218
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• 2007

고체 전해질로서 $CsH_2PO_4$결정은 $230^{\circ}C$ 이상에서 전기전도도가 $10^{-2}\;{\Omega}^{-1}cm^{-1}$의 값에 도달하는 초양성자(Superprotonic) 상태로 상전이를 한다. 이러한 이유로 $CsH_2PO_4$ 결정은 $230^{\circ}C$ 부근에서 사용할 수 있는 연료전지로 개발되어왔다. 실용적인 면에서 단결정의 경우보다 다결정의 물성 및 응용 연구가 많았는데, 입자 크기에 따른 체계적인 연구는 잘 이루어지지 않았다. 본 발표에서는 $CsH_2PO_4$ 다결정을 합성하여 SEM 및 micro Raman spectra를 조사하였다. SEM의 결과 입자들의 평균 크기는 100 nm 이었으며, micro Raman spectra는 Bulk $CsH_2PO_4$의 spectra 와 큰 차이를 보이지 않았다. $PO_4$의 내부진동은 거의 같은 주파수대를 보여주나, $300\;cm^{-1}$이하의 저주파 수 영역에서는 광학적 포논의 픽이 잘 보이지 않았다. 그 원인이 micro Raman 장치의 측정 특성인지, 물리적 변화인지는 확실치 않다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.201-203
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• 2007

본 논문에서는, 연료전지 시스템의 기계적 주변장치 (MBOP)와 전기적 주변장치 (EBOP)의 최적 설계를 위해서 PEMFC 스택을 전기화학반응을 기초로 모델링한다. 모델링을 위해 기본적인 PEMFC의 구조와 동작 원리를 설명한다. 연료전지의 이론적 최고 전압인 평형전위를 깁스 자유에너지와 네른스트 방정식으로 유도한다. 전류밀도에 따른 전압 손실인 활성화, 저항, 농도 분극현상을 표현하기 위해서 수식을 유도한다. 수소가 이온화되지 못하고 산소극으로 넘어가서 발생되는 연료손실 및 내부전류와 지속적인 정역반응인 교환전류도 모델링된다. 평형전압에서 각 분극을 뺀 실제 운전 전압을 시뮬레이션하고, 유량과 압력에 따른 출력 특성을 시뮬레이션 한다. 부하변동 시 출력특성을 시뮬레이터와 실험결과로 비교한다.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.269-275
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• 2004

Different biological tissues have different values of electrical resistivity. In EIT (electrical impedance tomography), we try to provide cross-sectional images of a resistivity distribution inside an electrically conducting subject such as the human body mainly for functional imaging. However, it is well known that the image reconstruction problem in EIT is ill-posed and the quality of a reconstructed image highly depends on the measurement error. This requires us to develop a high-performance EIT system. In this paper, we describe the development of a 16-channel digital EIT system including a single constant current source, 16 voltmeters, main controller, and PC. The system was designed and implemented using the FPGA-based digital technology. The current source injects 50KHz sinusoidal current with the THD (total harmonic distortion) of 0.0029% and amplitude stability of 0.022%. The single current source and switching circuit reduce the measurement error associated with imperfect matching of multiple current sources at the expense of a reduced data acquisition time. The digital voltmeter measuring the induced boundary voltage consists of a differential amplifier, ADC, and FPGA (field programmable gate array). The digital phase-sensitive demodulation technique was implemented in the voltmeter to maximize the SNR (signal-to-noise ratio). Experimental results of 16-channel digital voltmeters showed the SNR of 90dB. We used the developed EIT system to reconstruct resistivity images of a saline phantom containing banana objects. Based on the results, we suggest future improvements for a 64-channel muff-frequency EIT system for three-dimensional dynamic imaging of bio-impedance distributions inside the human body.

• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.71-77
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• 2014

The performance of catalysts for the recombination of oxyhydrogen gas was measured and compared with the results obtained from theoretical model. The oxyhydrogen gas was generated by the electrolysis cell and recombined through the fixed bed catalytic reactor. The yield that is the ratio of water-amount produced to the water-amount consumed in the electrolysis cell was increased with the increase of KOH concentration in electrolysis cell and the applied current. The catalyst 1 showed the best performance and the yield was under 60 %. The faradic yield calculated by Faraday's law showed about 100% in maximum with catalyst 1. The production rate of water generated by the recombination was 5-40 g/day dependent on the flow rate of mixed gas. Considering the results calculated from the pseudo-homogeneous catalytic reactor model, the hot point inside the reactor was moved to the direction of outlet and the maximum temperatures were $440-480^{\circ}K$ when the gas flow rate increased. The production rate of water calculated from the theoretical model showed good agreement with experimental results below the flow rate of $0.5cm^3/sec$, but there were much differences above that flow rate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.1
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• pp.16-20
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• 2005

In order to improve electrical conductivity and mechanical properties of 8YSZ SOFC electrolyte material, we used Al₂O₃ as an additive and applied the spark plasma sintering (SPS) method. The sintered bodies were densified above 96 ％ of theoretical density at 1200℃ and possessed microstructures composed of homogeneous grains less than 1 ㎛ in size. The addition of Al₂O₃ improved fracture toughness and bending strength by inhibiting grain growth of 8YSZ and increased total ionic conductivity because grain interior conductivity appeared to remain constant and grain boundary conductivity increased. It was assumed that the dissolution of Al₂O₃ into 8YSZ which was inevitable problem at commercial sintering method was effectively prohibited by the SPS technique with a relatively low sintering temperature and the reaction between Al₂O₃ and SiO₂ present at grain boundary to produce the crystalline Al/sub 2-x/Si/sub l-y/O/sub 5/ phase, resulting in the increase of grain boundary conductivity.