• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.147-151
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• 2007

A serpentine channel geometry often used in a polymer electrolyte membrane fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with relatively high aspect ratio active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compression conditions. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds to that of dropwise condensation in cathode channels.

• 태양에너지
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• 제18권3호
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• pp.63-69
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• 1998

일반적으로 건물 단열재는 건조된 것이 사용되며 이 상태에서 열전도율을 측정하여 열 손실을 산정할 때 기초자료로 이용될 수 있다. 그러나 이러한 단열재가 흡습성 재료인 경우에는 습도평형 혹은 다른 작용에 의해 습도가 높아지기에 이에 따라 열전도율도 상승하게된다. 이처럼 재료 열전도율의 상승효과는 건축물에 흡습성 재료가 사용될 경우 그 사이에 비흡습성 단열재료가 시공됐을 때도 양쪽재료의 흡습성으로 인하여 단열재의 열전도율이 상승하게 되며 이에 따른 열손실 또한 높아진다. 본 논문에서는 이러한 열전도율의 상승을 간단하게 계획단계에서 적용할 수 있도록 실측에 의해 검증된 약산식을 통해 산출될 수 있도록 하였다.

• 한국수소및신에너지학회논문집
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• 제23권4호
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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.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1028-1039
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• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• 한국의류학회지
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• 제19권4호
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• pp.637-650
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• 1995

The purpose of the study was to develop a model to explain how a fashion style is determined within a society and how the style diffuses. The research was carried out in two stages, theoretical study followed by empirical study. In the theoretical study, explanatory model about decision of fashion style and diffusion was developed and then fashion diffusion theories and fashion phenomenon of postholder society were explained by the model developed. The theoretical framework of the explanatory model was constructed in that fashion changes by ambivalence of pursuit values within an individual as well as within a society. The empirical study was carried out to validate the model by looking into fashion phenomenon in the postmodern society A questionnaire was developed including style image, pursuit value, preference style and administered to 19 to 30 year-old women living in Seoul area. Frequency distribution, discriminant analysis, one-way ANOVA. were used for the statistical analysis. As pursuit values differed in each style preference stoup, and pursuit value coincided with image of preference style it was confirmed that clothing selection behavior was determined by pursuit value. In a postmodern society where variety of values are pursued, appearance of various products and preference of all styles altogether considered, it could assume that subcultural collective selection phenomenon appeared.

• 열처리공학회지
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• 제16권4호
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• pp.197-204
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• 2003

Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 mm cell size, whereas 1:1.45 in 4 mm cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171.1 MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 mm cell size. And in 4mm cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores, It is thought to be main reason for lower flexural strength of 1.0 wt%C core.

• 한국환경보건학회:학술대회논문집
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• 한국환경보건학회 2005년도 국제학술대회
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• pp.286-288
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• 2005

This study was conducted to compare the fluoride concentrations in urine of preschool children aged 3${\sim}$6 years between residing in community water fluoridation area(Kwangju City) and non-fluoridation area(Sungnam City). The acid-diffusible fluoride in the urine and drinking water was isolated by the acid-diffusion technique and measured with a fluoride electrode. The mean daily fluoride excretion to urine of children residing in Kwangju and Sungnam were $1.27{\pm}0.75mgF^-$/g creatinine and $0.87{\pm}47 mgF^-$/g creatinine, respectively. It is concluded from this investigation that the $F^-$concentration in urine sample of kindergarten and drinking water of children living in Kwanju(fluoridated areas) were significantly higher than that of children living in Sungnam(non-fluoridated areas).

• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.167-170
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• 2012

A test-area molecular dynamics simulation method for the vapor-liquid interface of argon through a Lennard-Jones intermolecular potential is presented in this paper as a primary study of interfacial systems. We found that the calculated density profile along the z-direction normal to the interface is not changed with time after equilibration and that the values of surface tension computed from this test-area method are fully consistent with the experimental data. We compared the thermodynamic properties of vapor argon, liquid argon, and argon in the vapor-liquid interface. Comparisons are made with kinetic and potential energies, diffusion coefficient, and viscosity.

• 한국대기환경학회지
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• 제9권2호
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• pp.132-139
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• 1993

TCM has been used for many environmental impact assessments and many case studies in Korea. TCM was applied to urbvan areas and rolling terrains. But original TCM was developed for rural area, and this model could not reflect the characteristcs of these study sites. This paper analyzed the characteristics of TCM, and modified the algorithm of area source, and modified the vertical wind speed profile exponents and diffusion parameter to make it applicable in urban area. In the process of modification, an important error in area source calculation of original TCM program was found. So that was corrected as follows. $$ Before modification $QC = 0.79788456^*(0.5^*GRID)^**BA/(U(IA, IRUN)^*AA^*BA TCM09310$ After modification $QC = 0.79788456^*(500^*GRID)^**BA/(U(IA, IRUN)^*AA*BA) modified$ $$ Then original TCM and modified TCM-urban mode were compared, and it was found that predicted mean value by original TCM was 7 times higher than observed mean value. But mean value by modified TCM-urban mode was very similar to observed value.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 B
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• pp.312-314
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• 2000

The electric wave propagation characteristics of electromagnetic field by induction current shows a nonlinear distinction in the metal but linear on air. This paper is written about the magnetic transmission distinction in the metalic tube, which wrapped the center axis by the same direction. The electromagnetic field made by the transmission signal is transferred from the transmission coil area toward the receiving coil by the magnetic diffusion. So, it is different magnetic flux around the coil with one in the remote field area. Analyzing such a complex magnetic characteristic, we verified this theory by the vector analysis and presented eddy current mechanism and analytical model about magnetic distribution in the remote field area. This magnetic distribution rate in metal body will be very useful in the nondestructive inspection of the eddy current in remote field which is recently rising as a new technology.