• Solar Energy
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• v.13 no.2_3
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• pp.53-64
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• 1993

This study investigated heat transfer phenomena during the freezing of an initially superheated or non-superheated liquid in a cooled cylinder tube. Numerical and experimental method were performed to obtatin the temperature and velocity distribution, the shape of interface. Natural convection effects in the superheated liquid were confined and moderated a short freezing time. After natural convection ceases, heat conduction dominated in the whole paraffin, so Crystal and much-zone were found out in PCM. Initial superheating of liquid tended to morderatly diminish the frozen layer thickness at short freezing times but little effect on the these quantities at longer times. On the amount of frozen mass, Iintial liquid superheating is less affected than tube wall subcooling.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2008.11a
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• pp.423-427
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• 2008

지하수 중에 함유된 불소이온을 제거하기 위한 흡착제로 상용의 음이온교환수지(PA), 란탄산화물(La) 및 수산화아파타이트(HAp)를 선정하고 각각의 흡착특성을 회분식 실험을 통해 검토하였다. 그 결과를 요약하면 다음과 같다. 1) PA, La 및 HAp의 불소흡착은 Fruendlich isodtherm model 및 Pseudo-second-order kinetics model과 일치하는 거동을 보였다. 2) D-R model로부터 구한 흡착에너지는 9.66$\sim$12.90 kJ/mol로 이온교환메커니즘을 나타내는 흡착에너지 6$\sim$16 kJ/mol의 범위에 속하였다. 3) Van't Hoff 식에 이용하여 구한 ${\Delta}H^{\circ}$ 및 ${\Delta}G^{\circ}$값은 각각 3.40$\sim$89.28 kJ/mol과 -12.26$\sim$-13.76 kJ/mol의 범위를 보여 모두 흡착과정이 발열반응이며 자발적으로 일어나는 조건임을 알 수 있었다. 4) PA는 pH 6$\sim$8인 중성영역에서 가장 높은 불소 제거율을 보였으며, La과 HAp는 산성영역으로 갈수록 불소 제거율이 증가하는 특성을 나타내었다. 5) 불소에 대한 흡착선택성은 La$\geq$HAp>PA 순으로 높았으며, La의 경우 불소를 제외한 모든 음이온에 대한 흡착능이 없을 정도로 불소에 대한 흡착 특이성을 보였다.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.430-433
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• 2009

The development of large-scale environmental friendly livestock complex in the reclaimed tideland is one of different alternatives to increase the competitiveness of internal livestock industry against an international opening markets as DDA and FTA in agricultural field. Recently, it is possible to introduce an environmental friendly livestock complex in the reclaimed tideland by an amendment of the acts for agricultural land. However more studies that are on the basis of nitrogen and phosphorus mass balance need to preserve the agricultural environments as the quality of agricultural water and soil in rural area. In this study, the reference for feasibility study is Whaong reclaimed tideland which located at Whaseong city, Gyeonggi Province, and a basic concept of environmental friendly livestock complex is the production of forage crops with the supply of liquid fertilizer and the production of bioenergy such as biogas by the recycling of pig slurry as a resource. The mass balance of nitrogen based on between forage crops such as maize, barley and liquid fertilizer supplied at the reclaimed tideland, and also it was estimated an economical efficiency as anaerobic digestion plant for treating pig slurry of $100m^3/day$ introduce in an environmental friendly livestock complex.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.3
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• pp.88-94
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• 2006

In order to substitute current aluminum sabot and to increase the penetration performance of the kinetic energy projectiles, the research and development program for composites sabot has been conducted. For carbon/epoxy composites sabot, unidirectional carbon fiber reinforced epoxy prepreg was chosen and thick sectioned composites preforms with the different fiber angles along the circumferential direction of sabot were prepared by compression molding under the careful processing conditions at $150^{\circ}C$ for 1hour with $70kgf/cm^2$ curing pressure. The composites sabot demonstrated a weight reduction by approximately 30% than that of current aluminum sabot. The muzzle velocity of a kinetic energy projectile with composites sabot was measured to be about 63m/s higher than that with aluminum sabot. These results imply that the penetration performance is expected to be considerably increased when the composite sabot is applied to the kinetic energy projectiles.

• Journal of Hydrogen and New Energy
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• v.20 no.4
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• pp.323-330
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• 2009

Efficiency of a fuel cell is determined by the generated water. If water is not removed sufficiently, water will be accumulated at GDL, which causes flooding. Therefore, water control is regarded as a crucial factor to sustain fuel ell performance. In this study, PTFE coating on the surface of carbon paper was carried out to establish optimum process for hydrophobic treatment of GDL. Carbon paper was immersed at different concentrations of nano-sized PTFE coating solution. Their characteristics were analyzed systematically by FE-SEM, water contact angle, cyclic voltamogam, XRD and FT-IR. The quantitative correlation between the amount of coated-PTFE on a carbon paper and concentration of coating solution was carefully investigated. It is suggested that the amount of PTFE-coating on a carbon paper can be managed by means of controling concentration of coating solution.

• Journal of Hydrogen and New Energy
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• v.25 no.2
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• pp.131-138
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• 2014

Highly conductive bipolar plate for polymer electrolyte membrane fuel cell (PEMFC) was prepared using phenol novolac-type epoxy/graphite powder (GP)/carbon fiber filament (CFF) composite, and a rubber-modified epoxy resin was introduced in order to give elasticity to the bipolar plate graphite fiber (GF) was incorporated in order to improve electrical conductivity. To find out the cure condition of the mixture of novolac-type and rubber-modified epoxies, differential scanning calorimetry (DSC) was carried out and their data were introduced to Kissinger equation. And tensile and flexural tests were carried out using universal testing machine (UTM) and the surface morphology of the fractured specimen and the interfacial bonding between epoxy matrix and CFF or GF were observed by a scanning electron microscopy (SEM).

• New & Renewable Energy
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• v.2 no.4 s.8
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• pp.102-106
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• 2006

에탄올은 금속, 고무 수지를 부식시키고 열화시키기 때문에 FFV 등 알코올 대응차량이 아닌 경우 에탄올 허용도가 제한되고 있으며, 물과의 상호용해성과 흡습성으로 수분혼입에 의한 상분리가 발생하여 혼합가솔린의 유통에서의 취급에 어려움이 야기되고 있다. 또한, 에탄올은 가솔린과 혼합되면 공비현상으로 인하여 50% 유출온도가 크게 떨어지고 증기압이 7kPa 정도 상승을 초래하는 점도 간과하지 않을 수 없다. 따라서, 자동차용휘발유에 에탄올을 혼입하여 사용할 경우, 가솔린기재를 적절히 선택하여 적정품질을 유지하여야 하며 무엇보다도 에탄을 혼입농도에 따른 저장탱크와 주유기 등의 부품에의 영향과 저장시의 상분리 문제를 충분히 규명하여 유통인프라에서의 적절한 대응책이 마련되어져야 한다. 유통 인프라 대응을 위해서는 우선 생산단계에서 수분 혼입을 최소화하기 위하여 저유소의 출하지점에서 서브옥탄가솔린과 에탄올을 라인브랜딩에 의해 제조하는 방법이 가장 타당하며, 수송부문에서는 탱크로리 등의 공급라인인 파이프와 실링 재질 등에 대해서 면밀한 검토가 필요하다고 할 수 있다. 주유소에서의 대응은 에탄을 혼합연료와 직접 접촉하는 연료계 등 부품재질을 내부식성의 재질로 변환시켜야 하며, 수분혼입을 최소화하기 위한 이중탱크 설치, 지하탱크 환기구내의 대기벨브 설치 등이 필요하며, 기타, 품질 및 수분관리 대책 등도 마련되어야 할 것이다.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.105-110
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• 2011

The objective of this study is to analyze the characteristic of radiation environment in the urban and rural through the field observation in the summer. The radiation balance was compared through the measurement of the shortwave radiation and long-wave radiation in the urban, sub-urban, and rural. The following conclusion could be obtained from this research. (1) In the results of observation including the rain-day, it was found that the short wave radiance in the urban is lower about 10% than the rural. (2) The upper part of atmosphere layers in the urban area absorb much short wave radiation energies compared with the rural relatively. It can increase the temperature of the upper part of atmosphere layers and the emittance of long wave radiation. (3) The ratio of the downward short wave radiation to the downward long wave radiation was 1.24 for the urban, 1.28 for sub-urban and1.35 for rural. It can be estimated that the atmosphere condition of the rural is better than that of other areas.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.827-834
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• 2011

Epoxy/graphite/expanded graphite composites have been prepared in various weight ratios and thermal degradation and electrical properties were estimated in order to use for the bipolar plate materials in PEMFC. Thermogravimetric analysis (TGA) showed that the epoxy/graphite system cured by a curing agent GX-533 was most proper because its weight loss until $80^{\circ}C$ at which PEMFC would be operated was 0.3 wt%, and differential scanning calorimetry (DSC) analysis showed its cure temperature would be sufficient at $80^{\circ}C$. The activation energy for the cure reaction was 132.0 kJ/mol and the pre-exponential factor was $1.76{\times}10^{17}min^{-1}$. Electrical conductivity on the surface of the bipolar plate prepared under a pressure of 200 $kgf/cm^2$ was increased from 4 to 25 $S/cm^2$ by increasing expanded graphite (EG) content from 50 phr to 90 phr. The percolation threshold was initiated around 75 phr and the corrosion rate at 80 phr was 1.903 $uA/cm^2$.

• Journal of Hydrogen and New Energy
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• v.30 no.6
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• pp.629-634
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• 2019

Dicyclopentadiene is a low viscosity resin which forms a poly-dicyclopentadiene rapidly through ring opening metathesis polymerization (ROMP). This poly-dicyclopentadiene has outstanding properties of low-temperature, water and impact resistances. Due to these advantages, military and offshore structures try to apply the DCPD composites by using liquid composite molding process. In this study, 14%, 38% volume fraction fiber glass strand mat reinforced p-DCPD composites processed by structural reaction injection molding (S-RIM) which has resin-catalsyt mixing head and glass fiber preform in the mold. Additionally, S-RIM numerical analysis was conducted to predict the process time depending on fiber volume fraction and mold temperature. The process time is shorter when it has the lower fiber volume fraction or the higher mold temperature. At higher mold temperature, it is necessary to set the maximum mold temperature considering the resin curing time.