• Transactions on Electrical and Electronic Materials
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• 제3권1호
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• pp.4-8
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• 2002

The typical mold method for FED (field emission display) fabrication is used to form a gate electrode, a gate oxide layer, and emitter tip after fabrication of a mold shape using wet-etching of Si substrate. However, in this study, new mold method using a side wall space structure was developed to make sharp emitter tips with the gate electrode. In new method, gate oxide layer and gate electrode layer were deposited on a Si wafer by LPCVD (low pressure chemical vapor deposition), and then BPSG (Boro phosphor silicate glass) thin film was deposited. After then, the BPSG thin film was flowed into the mold at high temperature in order to form a sharp mold structure. TiN was deposited as an emitter tip on it. The unfinished device was bonded to a glass substrate by anodic bonding techniques. The Si wafer was etched from backside by KOH-deionized water solution. Finally, the sharp field emitter array with gate electrode on the glass substrate was formed.

• 한국환경과학회지
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• 제20권12호
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• pp.1599-1605
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• 2011

To evaluate heat environment surrounding plants diurnal change of leaf temperature in the broad-leaved deciduous and evergreen trees was measured with microclimatic environmental factors including global solar radiation, and upward and downward long wave radiation. Maximum daily solar radiation was 961.2 and 976.3 w/$m^2$ in August 9 and 23, respectively. Upward long wave radiation was slightly higher than downward long wave radiation, showing 404.2 w/$m^2$ in August 9 and 394.5 w/$m^2$ in August 23. In addition, daily maximum vapor pressure deficit was 5.42 and 6.84 kPa in August 9 and 23, respectively, indicating high evaporative demand. Quercus glauca and Acer mono was differently responded to changing light regimes. On August 9, leaf temperature at the top-positioned leaves of Acer plants was higher than air temperature as well as those of Quercus plants in the morning. This indicates that stomata in Acer plants were closed by heat stress or water stress in the morning, while Quercus plant maintained active transpiration by opening stomata. These results indicated that improved light regimes such as gap opening in the closed forest may not always affect positively in the physiology of understory plants.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.53-56
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• 2006

KOMPSAT (KOrea Multi-Purpose SATellite)-5 for the earth observation and scientific research is scheduled to launch in 2009. The second payload, AOPOD (Atmosphere Occultation and Precision Orbit Determination) system, consists of a space-borne dual frequency GPS receiver and a laser retro reflector. GPS radio occultations from AOPOD system can be used to generate profiles of refractivity, temperature, pressure and water vapor in the neutral atmosphere with a high vertical resolution. Also the radio occultation in the ionosphere provides an inexpensive tool of vertical electron density profile. Currently, many LEO missions with GPS radio occultation receivers are on orbit and more GPS occultation missions are planed to launch in the near future. In this paper, we simulated radio occultation measurements from KOMPSAT-5 and retrieved atmospheric profiles using the simulated data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.320-325
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• 2010

A multiphase CFD analysis is performed to investigate the effect of near-wall grid for simulating a subcooled boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and vapor(steam) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit ($y_{w}^{+}$) was examined from 64 to 172 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., $y_{w}^{+}$ > 100.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1237-1244
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• 2001

An experimental study was carried out to identify the various regimes of natural convective pool boiling and to determine the boiling heat transfer curve and Critical Heat Flux(CHF) on a vertical square surface having a 70mm width and a 70mm height. The heater made of copper block with embedded cartridge heaters is submerged in a water tank at atmospheric pressure. As the heat flux increases from 100kW/㎡ to 1.2MW/㎡, the heat transfer regime migrates from the nucleate boiling to the film boiling. The boiling heat transfer data are fitted by Rohsenow type correlation. An explosive vapor generation on the heated surface, whose size and frequency are characterized by the heat flux, is visualized using a high speed digital imaging system.

• Korean Chemical Engineering Research
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• 제49권3호
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• pp.367-371
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• 2011

TBAB(tetra-n-butyl ammonium bromide)는 상온/상압 조건에서 semi- clathrate를 형성하는 물질로서 최근 가스 하이드레이트 형성법을 이용한 천연가스 수송 및 저장, 기체분리 공정 등에서 열역학적 촉진제로 주목받고 있다. 본 연구에서는 TBAB의 열역학적 촉진제로서의 특성을 알아보기 위해 $CH_{4}$+TBAB와 $CO_{2}$+TBAB 혼합 하이드레이트계에 대하여 TBAB 농도(5, 32 wt%)에 따른 가스 하이드레이트 3상(하이드레이트(H)-물($L_{w}$)-기상(V)) 평형 조건을 측정하였다. 혼합 하이드레이트의 경우 TBAB의 농도가 5 wt%일 때에 비해 32 wt%일 경우에 열역학적 촉진 효과가 훨씬 크게 나타나는 것을 알 수 있었으며, 이는 순수 TBAB semi-clathrate의 농도별 상압 해리 온도 경향과 유사하였다. 또한, $^{13}C$ NMR 분석을 통하여 $CH_{4}$ + TBAB 혼합 하이드레이트의 동공에 $CH_{4}$ 기체가 포집되어 있음을 확인하였고 이 동공의 특성이 순수 $CH_{4}$ 하이드레이트(구조-I)의 작은 동공($5^{12})$과 동일함을 확인할 수 있었다.

• 설비공학논문집
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• 제20권4호
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• pp.274-279
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• 2008

In the perspective of saving energy in buildings, high performance of insulation and air tightness for improving the heating and the cooling efficiency has brought the positive effect in an economical view. However, these building energy saving technologies cause the lack of ventilation, which is the direct cause of increasing the indoor contaminants, and it is also very harmful to residents because they spend over 90% of their time in the indoor area. Therefore, the ventilation is important to keep indoor environment clean and it can also save energy consumption. In this study, a HEPA type breathing wall is designed as a passive ventilation system to collect airborne particles and to supply fresh outdoor air. To make fine porous structures, polymer nano fibers which were made by electro spinning method are used as a precursor. The nano fibers are coated with SiO2 nano particles and finally the HEPA type breathing wall is made by sintering in the electric furnace at $300\sim500^{\circ}C$. The pressure drops of nano ceramic structure are 8.2, 25.5 and 44.9 mmAq at the face velocity of 2.0, 5.9 and 8.8 cm/s, respectively. Also the water vapor permeability is $3.6g/m^2{\cdot}h{\cdot}mmHg$. In this research, the porous nano ceramic structures are obtained and the possibility for the usage of a material for HEPA type breathing wall can be obtained.

• 한국기계가공학회지
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• 제17권3호
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• pp.51-58
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• 2018

In this paper, the organic material Poly(methyl methacrylate) PMMA is used with inorganic $Al_2O_3$ to fabricate organic-inorganic multilayer barrier thin films. The organic thin films are developed using a roll-to-roll electrohydrodynamic atomization system, whereas the inorganic are grown using a roll-to-roll low-temperature atmospheric pressure atomic layer deposition system. For the first time, these two technologies are used together to develop organic-inorganic multilayer barrier thin films in atmospheric condition. The films are grown under optimized parameters and classified into three classes based on the layer structures, when the total thickness of the barrier is maintained at ~ 160 nm. All classes of barriers show good morphological, optical and chemical properties. The $Al_2O_3$ films with a low average arithmetic roughness of 1.58 nm conceal the non-uniformity and irregularities in PMMA thin films with a roughness of 5.20 nm. All classes of barriers show a notably good optical transmission of ~ 85 %. The hybrid organic-inorganic barriers show water vapor and oxygen permeation in the range of ${\sim}3.2{\times}10^{-2}g/m^2/day$ and $0.015cc/m^2/day$ at $23^{\circ}C$ and 100% relative humidity. It has been confirmed that it can be mass-produced and used as a low-cost barrier thin film in various printing electronic devices.

• 한국분무공학회지
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• 제24권1호
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• pp.35-42
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• 2019

Syngas is widely produced by incomplete combustion of coal, water vapor, and air (oxygen) in a high-temperature/high-pressure gasifier through a coal-gasification process for power generation. In this study, a simulation syngas which was mainly composed of $H_2$, CO, $CO_2$, and $N_2$ was fueled with diesel. A modified single cylinder compression ignition (CI) engine is equipped with intake port syngas supply system and mechanical diesel direct injection system for dual fuel combustion. Combustion and emission characteristics of the engine were investigated by applying various syngas composition ratios and compression ratios. Diesel fuel injection timing was optimized to increase indicated thermal efficiency (ITE) at the engine speed 1,800 rpm and part load net indicated mean effective pressure ($IMEP_{net}$) 2 to 5 bar. ITE of the engine increased with the $H_2$ concentration, compression ratio and engine load. With 45% of $H_2$ concentration, compression ratio 17.1 and $IMEP_{net}$ 5 bar, ITE of 41.5% was achieved, which is equivalent to that of only diesel fuel operation.

• 태양에너지
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• 제15권3호
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• pp.29-38
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• 1995

본 연구는 화학열펌프 개발을 목적으로 비교적 고온영역에서 화학축열에 응용 가능 할 것으로 판단되는 무기수화물계 $Ca(OH)_2/CaO$ 가역 반응싸이클을 이용한 수화 탈수반응에 따른 충진층내 열이동에 대하여 실험적 검토를 행하였다. 그 결과 본 실험에서 얻은 열교환특성은 $Ca(OH)_2$ 열분해 탈수반응시 반응기 내의 시료층 상단부가 하단부에 비해 탈수반응이 느리게 진행되었으며 이러한 현상은 탈수반응이 하부에서 상부로 진행됨을 알 수 있었다. 또, 반응기내 반경방향에서의 $Ca(OH)_2$ 열분해 탈수반응에 따른 온도변화는 시료 중심부에서 상 하단부로 나타났으며 이는 열전도도에 의한 온도 강하로 중심부의 축열온도가 높음을 알 수 있었다.