• 반도체디스플레이기술학회지
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• 제16권1호
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• pp.106-111
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• 2017

When a substrate with a pixel-defining layer (bank) is coated, there arises capillary force due to surface tension and adhesive forces between a solvent and the bank layer. It brings in a degradation of film thickness and emission uniformities within pixels. With an attempt to suppress it, we have performed fluid flow simulations of capillary arise by varying the contact angle of bank and the bank structure. We have first demonstrated that the fluid flow model can reproduce the capillary phenomenon that was observed experimentally. It has been found that capillary arise can be suppressed using a hydrophobic material for the bank layer. Furthermore, it was suppressed by tilting the sidewalls outwardly (i.e., using a positive photoresistor). We can obtain very uniform films when the slope is $50^{\circ}$ with the contact angle of $40^{\circ}$.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2029-2038
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• 2024

A deep understanding of the characteristics and mechanism of geyser boiling and capillary pumping is necessary to optimize a high-temperature sodium heat pipe. In this work, the Volume of Fluid (VOF) two-phase model and the capillary force model in the mesh wick were used to model the complex phase change and fluid flow in the heat pipe. Computational Fluid Dynamics (CFD) simulations successfully predicted the process of bubble nucleation, growth, aggregation, and detachment from the wall in the liquid pool of the evaporation section of the heat pipe in horizontal and tilted states, as well as the reflux phenomenon of capillary suction within the wick. The accuracy and stability of the capillary force model within the wick were verified. In addition, the causes of geyser boiling in heat pipes were analyzed by extracting the oscillation distribution of heat pipe wall temperature. The results show that adding the capillary force model within the wick structure can reasonably simulate the liquid backflow phenomenon at the condensation; Under the horizontal and inclined operating conditions of the heat pipe, the phenomenon of local dry-out will occur, resulting in a sharp increase in local temperature. The speed of bubble detachment and the timely reflux of liquid sodium (condensate) replenishment in the wick play a vital role in the geyser temperature oscillation of the tube wall. The numerical simulation method and the results of this study are anticipated to provide a good reference for the investigation of geyser boiling in high-temperature heat pipes.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.92-96
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• 2019

In the presence of ${\mu}-tip$ embedded in a slot-die head for stripe coatings, there arises the capillary flow that limits an increase of the stripe density, which is required for the potential applications in organic light-emitting diode displays. With an attempt to suppress it, we have employed a computational fluid dynamics software and performed simulations by varying the ${\mu}-tip$ length and the contact angles of the head lip and ${\mu}-tip$. We have first demonstrated that such a capillary flow phenomenon (a spread of solution along the head lip) observed experimentally can be reproduced by the computational fluid dynamics software. Through simulations, we have found that stronger capillary flow is observed in the hydrophilic head lip with a smaller contact angle and it is suppressed effectively as the contact angle increases. When the contact angle of the head lip increases from $16^{\circ}$ to $130^{\circ}$, the distance a solution can reach decreases sharply from $256{\mu}m$ to $44{\mu}m$. With increasing contact angle of the ${\mu}-tip$, however, the solution flow along the ${\mu}-tip$ is disturbed and thus the capillary flow phenomenon becomes more severe. If the ${\mu}-tip$ is long, the capillary flow also appears strong due to an increase of flow resistance (electronic-hydraulic analogy). It can be suppressed by reducing the ${\mu}-tip$ length, but not as effectively as reducing the contact angle of the head lip.

• 한국지반공학회논문집
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• 제26권4호
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• pp.37-45
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• 2010

기후변화로 인해 물의 증발량이 많은 지역의 지반에서는 자연적인 소금의 고결화 현상이 발생한다. 이러한 소금의 고결화 분포는 모래지반에서 모세관력에 영향을 받는다. 이 연구의 목적은 콘 관입시험, 전기전도율 측정, 사진 이미지 촬영, 비파괴 이미지 분석 그리고 탄성파에 의한 프로세스 모니터링을 이용하여 소금의 고결화 현상에 대한 모세관력의 효과를 관찰하는 것이다. 실험은 입상재료를 모형화한 글라스비즈를 소금물에 포화시킨 후, 오븐에 넣어 시료를 건조시킴으로써 고결화를 발생시켰다. 실험결과, 고결된 소금의 농도는 시료입경이 작은 경우 최상부에서 높았고, 시료입경이 큰 경우 중간 또는 하부에서 높았다. 고결된 시료에서 높은 소금농도의 위치는 해석적 방법으로 산정된 모세관 높이와 유사하였다. 본 연구에서 수행한 5가지 실험은 모세관력이 소금이 고결된 흙과 같은 입상재료의 거동에 중요한 영향을 끼치는 것을 보여준다.

• 대한환경공학회지
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• 제22권7호
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• pp.1285-1294
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• 2000

본 연구는 모세관 사이폰 현상을 이용한 부유물질제거 장치를 사용하여 부유물질제거 가능성 및 처리수량과 수질에 미치는 영향인자에 대하여 검토하였다. 처리유량은 누적처리시간과 모세관 사이폰 유입부 수두가 클수록 작아지는 반면에 처리수 수질은 향상되는 경향을 보였다. 한계 flux를 $107{\ell}/m/day$로 하고, 응집제를 각각 0, 0.45, $1.82mg/{\ell}$ (as $Al^{+3}$)로 주입하였을 때 처리수 탁도는 평균 2, 1, 0.5NTU를 보였고, 15~17일간 운전하는 동안 세척수량은 처리수량의 약 0.5~0.7%가 사용되었다. 따라서, 모세관 사이폰 현상을 이용한 부유물질제거 장치는 정수처리공정 중의 응집침전과 급속여과공정에 적용할 수 있을 것으로 기대된다.

• Bulletin of the Korean Chemical Society
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• 제24권1호
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• pp.81-85
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• 2003

Direct analysis of microbes such as either gram-positive or gram-negative bacteria without cell lysis was investigated using capillary electrophoresis. Bacteria cells were directly introduced into the microbore fusedsilica capillary, then separated under high electric field in less than 15 min. It was found that a proper dispersion of bacteria cells was important for reproducible results. Migration behavior of bacteria at different storage condition was investigated and many unexpected peaks were observed from bacteria stored at room temperature due to the distortion of cells. This phenomenon was attributed to the change of size and shape of the same bacterium and confirmed by the scanning electron microscopic images.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.710-716
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• 2006

Micro-PIV system with a high speed CCD camera is used to measure the flow field near the advancing meniscus of a water slug in microchannels. Image shifting technique combined with meniscus detecting technique is proposed to measure the relative velocity of the liquid near the meniscus in a moving reference frame. The proposed method is applied to an advancing front of a slug in microchannels with rectangular cross section. In the case of hydrophilic channel, strong flow from the center to the side wall along the meniscus occurs, while in the case of the hydrophobic channel, the fluid flows in the opposite direction. Further, the velocity near the side wall is higher than the center region velocity, exhibiting the characteristics of a strong shear-driven flow. This phenomenon is explained to be due to the existence of small gaps between the slug and the channel wall at each capillary corner so that the gas flows through the gaps inducing high shear on the slug surface. Simulation of the shape of a static droplet inside a cubic cell obtained by using the Surface Evolver program is supportive of the existence of the gap at the rectangular capillary corners. The flow fields in the circular capillary, in which no such gap exists, are also measured. The results show that a similar flow pattern to that of the hydrophilic rectangular capillary (i.e., center-to-wall flow) is always exhibited regardless of the wettability of the channel wall, which is also indicative of the validity of the above-mentioned assertion.

• Journal of Advanced Marine Engineering and Technology
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• 제37권4호
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• pp.351-357
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• 2013

플립칩 패키징에서 언더필 공정은 칩과 기판 사이를 에폭시로 채워서 본딩하는 공정으로 제품의 신뢰성 향상을 위해 수행되어 진다. 이 언더필 공정은 모세관 현상에 의해서 이루어지는데 유체의 계면과 범프의 배열이 계면 운동에 미치는 영향으로 인하여 공정 중 예기치 않은 공기층을 형성하게 된다. 본 연구에서는 모세관 언더필 유동에서 나타나는 비정상 계면 유동을 가시화하여 범프 배열에 따른 레이싱 효과와 계면의 병합 현상에 대하여 고찰하였다. 그 결과, 플립칩 내부의 범프가 고밀도일수록 유체의 흐름방향과 수직방향의 유동이 더욱 활발하게 진행되어 더 많은 공기층이 형성되었으며, 엇갈린 배열일 경우 직각 배열에 비해 이러한 현상이 더 지배적으로 나타난다.

• 대한기계학회논문집
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• 제12권4호
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• pp.825-832
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• 1988

본 연구에서는 1차원 열흐름하에서 상부가 가열된 다공물질내의 열파이프 현 상과 관련하여 2상영역의 존재와 그 길이에 영향을 미치는 인자들을 실험적으로 관찰, 조사하였다.

• 한국가시화정보학회지
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• 제10권1호
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• pp.21-26
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• 2012

Hydrophobic characteristics of high temperature metal surface were investigated by high-speed visualization of water droplet impact. An aluminum plate was used as the sample plate and the initial diameter of a water droplet was 2 mm. Transient behavior of a single droplet impinging on the surface with and without heating was captured by using a high speed camera running at 4,000 frames per second. The Leidenfrost phenomenon was demonstrated for the case of $300^{\circ}C$ surface temperature, however there was no rebounding of droplet on the cold plate due to hydrophilic nature. The experimental results show that the shape evolution of a droplet impinging on the surface varies with the Weber number, i.e. the ratio of impact inertia to capillary force. The overall water-repellent characteristics of the heated surface was very similar to that of the super hydrophobic surfaces.