• 에너지공학
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• 제8권2호
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• pp.333-340
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• 1999

과냉수에서의 난류 증기응축 제트에 대한 수치해석 연구가 수행되었다. 증기와 과냉수 사이에 국부 균질유동을 가정하고 난류 특성은 난류 확산화염에서 사용되는 $textsc{k}$-$\varepsilon$-g 모델을 사용하여 증기응축 유동 현상에 대한 물리적 모델을 제안하였다. 즉, 난류는 난류 운동 에너지와 운동 에너지 소멸률로 모사되고 증기와 과냉수의 혼합률비에 대한 평균값과 변동량에 대한 미분 방정식을 추가하여 직접 풀고 혼합률비에 확률분포 함수를 적용하여 열역학 변수의 평균값을 구한다. 증기 질량 유속, 과냉수 온도와 노즐 직경을 변화시키며 증기응축제트의 특성을 해석하였다. 본 해석에 사용된 모델을 평가하기 위해 기존의 실험 데이터를 사용해서 수치해석 결과와 실험치를 비교하여 만족할 만한 결과를 얻었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 지반공학 공동 학술발표회
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• pp.382-388
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• 2005

Soil vapor extraction(SVE) is an effective and cost efficient method of removing volatile organic compounds(VOCs) and petroleum hydrocarbons from unsaturated soils. However, soil vapor extraction becomes ineffective in soils with low gas permeability, for example soils with air permeabilities less than 1 Darcy. Prefabricated vertical drains(PVDs) have been used for dewatering fine-grained soils for more than 25 years. Incorporating PVDs in and SVE system can extend the effectiveness of SVE to lower permeability soils by shortening the air flow-paths and ultimately expediting contaminant removal. The objective of the work described herein was to effectively incorporate PVDs into a SVE remediation system and to demonstrate a PVDs enhanced SVE system at full scale. The finding from this research will facilitate the design of field PVD-SVE systems in terms by providing insight into the optimal spacing between PVDs, the radius of influence of the wells and the flow rates to be used to capture and extract gas phase contaminants.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.915-920
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• 2001

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston bowl shapes(F, B, and R-type) in a optically accessible engine. The images of liquid and vapor phases were captured in the motoring engine using exciplex fluorescence method. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure is 5.1MPa. Two dimensional spray fluorescence image of vapor phases was acquired to analyze spray behaviors and fuel distribution inside of cylinder. Four injection timings were set at BTDC $90^{\circ},\;80^{\circ},\;70^{\circ},\;and\;60^{\circ}$. With a fuel injection timing of BTDC $90^{\circ}$, fuel-rich mixture level in the center region was highest in a B-type piston. With a fuel injection timing of BTDC $60^{\circ}$, R-type piston was best. R-type piston shape was suitable under enhanced swirl ratio and late injection condition and B-type piston shape was right in a weak swirl ratio. It was found that the piston bowl shape affected the mixture stratification inside of cylinder.

• 대기
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• 제18권4호
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• pp.417-427
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• 2008

In this paper, we analyzed the physical and thermodynamic characteristics of fog by using the integrated water vapor (IWV) from Global Positioning System (GPS) networks and the regular observation data of meteorological stations in GPS sites. The cases of a radiation and an advection fog were selected as samples, the conversions of water substance from the water vapor to cloud water in fog were detected by the Bulk Water-Continuity Model, and the pattern analysis is adapted on GPS IWV, temperature, wind and relative humidity. Under the specific hypothesis (saturation and stable), GPS IWV could detect quantitatively the phase changing between the water vapor and cloud water content with condensation/evaporation during the formation and dissipation of fog. After it reaches to the saturation, the relative humidity can be a limited indicator for fog. However, GPS IWV can detect the status change of fog even after the saturation. It has indicated that GPS IWV could be a new observing technique for the processes of the fog formation and the dissipation.

• Nuclear Engineering and Technology
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• 제36권2호
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• pp.142-152
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• 2004

The liquid entrainment and vapor pull-through offtake model of RELAP5/MOD3 had been developed for SBLOCA (Small Break Loss of Coolant Accident). The RELAP5/MOD3 model for horizontal volumes accounts for the phase separation phenomena and computes the flux of mass and energy through a branch when stratified conditions occur in the horizontal pipe. In the case of CANDU reactor, this model should be used in the coolant flow of 95 feeders connected to the reactor header component under the horizontal stratification in header. The current RELAP5 model can treat the only 3 directions junctions; vertical upward, downward, and side oriented junctions, and thus improvements for the liquid entrainment and vapor pull-through model were needed for considering the exact angles. The RELAP5 off-take model was modified and generalized by considering the geometric effect of branching angles. Based on the previous experimental results, the critical height correlation was reconstructed by use of the branch line connection angle and validation analyses were also performed using SET. The new model can be applied to vertical upward, downward and angled branch, and the accuracy of the new correlations is more improved than that of RELAP5.

• 한국유체기계학회 논문집
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• 제11권3호
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• pp.7-13
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as pump, turbine, nozzle, Infector, etc. In the present work, a solver for two-phase flows has been developed and applied to simulate the cavitating flows past hydrofoils. The governing equation is the two-phase Navier-Stokes equation, comprised of the continuity equation of liquid and vapor phase. The momentum and energy equation is in the mixture phase. The solver employs an implicit, dual time, preconditioned algorithm using finite difference scheme in curvilinear coordinates. An experimental data and other numerical data were compared with the present results to validate the present solver. It is concluded that the present numerical code has successfully accounted for two-phase Navier-Stokes model of cavitation flow.

• 한국세라믹학회지
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• 제27권5호
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• pp.677-683
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• 1990

Melt-textured growth of the YBa2Cu3O7-x phase from a supercooled melt created locally aligned, barshaped grains of the orthorhombic 1-2-3 phase. Based on all the observed phenomena, the gross mechanism of the melt-textrued growth of YBa2Cu3O7-x on the (100) plane of MgO was delineated by three basic patterns of reactions. These are : (ⅰ) formation of the aligned 1-2-3 phase and the Y-rich 2-1-1 phase at the bulk region away from the (100) plane of MgO ; (ⅱ) formation of the Cu-richprecipitates at the interfacial region by the selective interface-induced precipitation of the liquid phase ; (ⅲ) condensation reaction of the entrapped Cu-rich vapor with Mg atoms during the initial stage of rapid cooling from 130$0^{\circ}C$ to 98$0^{\circ}C$.

• 한국결정성장학회지
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• 제8권4호
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• pp.634-639
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• 1998

$Y_2O_3$와 $Nb_2O_5$가 첨가된 지르코니아에 입자 크기가 다른 두종류의 Al2O3를 부피비로 10~30% 첨가한 복합체를 155$0^{\circ}C$ 온도에서 5시간 소결하여 $250^{\circ}C$ 온도의 공기 분위기하에서 1000시간 혹은 $180^{\circ}C$ 온도의 0.3MPa H2O vapor pressure 분위기하에서 5시간 열처리를 하여 X-ray 회절분석 방법을 이용하여 저온 상안정성을 조사하였다. 복합체 전부 열처리 후에 정방정 상에서 단사정 상으로 상전이가 발생하지 않는 우수한 저온 상안정성이 관찰되었다. 복합체의 상아정성에 Nb 첨가가 $Al_2O_3$의 첨가보다 더 효과적이었다. 2.8$\mu$m 입자크기를 가진 Al2O3를 부피비로 20% 첨가한 복합체에서 최적의 조건이 관찰되었으며 강도와 인성값은 각각 670MPa와 7.1MPam1/2이었다. Al2O3 입자 크기가 2.8$\mu$m에서 0.2$\mu$m로 감소함에 따라 강도는 다소 증가하였으나 파괴인성값은 감소하였다.

• 화약ㆍ발파
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• 제37권4호
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• pp.10-16
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• 2019

충격파나 압력파가 구조물에 미치는 영향을 평가하기 위해서는 과압, 양의 압력 지속시간, 충격량에 대한 정보가 필요하다. 본 연구에서는 증기운 폭발 해석에 효과적인 다중에너지법을 적용하여 과압 및 양의 압력 지속 시간을 결정하였다. 영국 Nypro 화학회사에서 발생한 싸이클로헥산 증기운 폭발 사고에서 추정된 총 폭발열을 기반으로 폭발원으로부터 40, 80, 120, 160, 200, 240, 280, 320, 360(m) 이격된 지점에서의 과압, 양의 압력 지속시간을 평가하였다. 거리에 따라 과압은 지수적으로 감소하는 것으로 나타났고, 양의 압력 지속시간은 거의 선형적으로 증가하는 것으로 나타났다. 상기의 각 거리에서 구한 과압 및 충격량을 이용하여 각 거리에서의 구조물의 손상 확률을 평가하기 위해서 프로빗 함수를 사용하였다. 손상 확률을 평가한 결과 120m 이내 지점에서는 붕괴의 가능성이 크고, 240m 이내에서는 심각한 구조물의 손상이, 구조물의 가벼운 손상과 유리창 파손은 전 범위에 걸쳐서 발생하는 것으로 나타났다.

• 한국결정학회지
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• 제8권1호
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• pp.33-37
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• 1997

(1012)면 사파이어 기판위에서 성장되는 (12f10)면 GaN 이종적층막의 광학적 특성을 연구하였다. GaN 이종적층막은 $Ga/HC1/NH_3/He$계를 사용한 HVPE(halide vapor phase epitaxy)방법에 의하여 $990^{\circ}C$의 온도에서 성장시켰다. 이종적층막의 표면조직과 결정구조는 XRD, RHEED와 SEM으로 확인하였다. 결정구조가 확인된 (1210)면 GaN 단결정막의 광학적 특성은 PL과 Ra-man으로 관찰하였다. Raman 측정은 광학적포논에 기인된 활성모드를 결정축에 대하여 레이저빔의 편광과 진행방향에 의해 변화하는 것을 관찰하였다. Y(Z, Y & Z) X 방향에서의 측정은 $A_1(TO)=533\;cm^{-1},\;E_1(TO)=559\;cm^{-1}$과 $E_2=568\;cm^{-1}$ 모드에 기인된 Raman 스펙트럼을 관찰할 수 있었으며 Z(Y, Y & Z) X 방향에서의 측정은 $E_2$포논 만이 검출되었다.