• 한국입자에어로졸학회지
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• 제6권1호
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• pp.1-7
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• 2010

Generally, large amounts of DOP(Di-Octyl Phthalate) chemicals are used as plasticizers in PVC compound manufacturing processes. However, it is very important to collect DOP species immediately from a workplace in order to protect worker's heath and recover them. To accomplish these objectives, we need to understand the droplet formation and growth mechanisms of DOP species. In this study, two important parameters such as temperature gradient and residence time were considered to clarify these mechanisms. We found that residence time is very critical to determine the droplet size distribution of DOP, whereas temperature gradient in general operating conditions(less than $-6.8^{\circ}C/cm$) is negligible.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.641-647
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• 2016

피에조 DOD(drop-on-demand) 잉크젯 프린팅 방식은 다양한 종류의 잉크를 사용할 수 있기 때문에 최근에 첨단 산업에 적용이 활발히 연구되고 있다. 피에조 잉크젯 헤드에서 토출되는 액적의 형성 과정을 VOF(Volume-of-Fluid) 기법을 이용한 전산해석으로 예측하고 이를 측정결과와 비교하였다. 작동유체는 에틸렌 글리콜 50%와 IPA(Isopropil alchol) 50%의 혼합액을 사용하였다. 노즐 출구에서 메니스커스 변위의 시간에 따른 변화를 직접 측정하여 노즐 입구의 속도분포를 예측하고 이를 해석의 초기조건 입력자료로 사용하였다. 측정치와 해석치를 비교한 결과 전산해석이 측정치의 액적 형성 과정을 잘 예측함을 알 수 있었다. 주액적 형성과정보다 위성액적 형성과정 예측에 오차가 약간 컸는데, 이는 정지중의 공기에 큰 질량의 주액적이 날아가는 것을 예측할 때는 해석오차가 적지만 주액적에 의해서 주변 공기 유동이 활발해진 상태에서 적은 질량의 위성액적이 날아가는 것을 예측할 때는 해석오차가 상대적으로 커지기 때문이다. 또한 에틸렌 글리콜과 IPA의 혼합 비율을 달리하여 물성치를 변화시킨 다른 잉크에 대해서도 잉크 액적 형상을 예측한 결과 실험 결과를 비교적 정확히 예측할 수 있었다.

• Korean Chemical Engineering Research
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• 제48권5호
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• pp.545-555
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• 2010

최근 액적 기반의 미세유체 시스템은 물리, 화학, 생물학등의 기초과학과 재료과학 분야까지 매우 폭넓게 활용되고 각광받고 있는 기술분야이다. 본 총설은 액적기반 미세유체 시스템의 미세유체 반응기 제작 기술, 액적 형성 원리, 액적 혼합 및 제어, 그리고 새로운 기능성 재료의 합성등의 폭넓은 응용분야에 관해 자세하게 소개하고자 한다. 더불어 액적기반 미세유체 시스템의 가장 큰 장점인 입자의 크기 조절 방법, 형태, 모양 및 구조의 제어 기술에 관해 논의하고자 한다.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2003년도 기술심포지움 논문집
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• pp.122-127
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• 2003

본 논문에서는 새로운 솔더 범프 형성 방법 중의 하나인 Solder droplet jetting에 의한 솔더 범프 형성 공정에 대해 연구하였으며, 이를 위해 솔더 제팅 직후의 안정한 솔더 액적(solder droplets)의 형성을 위한 공정 변수들의 영향에 대해 먼저 알아보았다 이를 위해 제팅 노즐에 가해지는 파형과 용융 솔더의 온도, 질소 가스의 압력 등에 의한 영향을 주로 살펴보았다. 다음으로 리플로를 거쳐 솔더 범프를 형성하였으며, 다양한 크기의 솔더 범프를 간단한 방법으로 형성하였다. 또한 무전해 니켈/솔더 계면 반응과 Bump shear test를 통한 기계적 성질을 고찰하는 한편, 계면 반응 결과는 스크린 프린팅에 의해 형성된 솔더 범프의 결과와 비교함으로써, 저가의 공정으로 미세 피치를 갖는 솔더 범프를 형성할 수 있는 Solder droplet jetting 방법이 기존의 방법에 의해 형성된 솔더 범프의 특성과 유사함을 고찰하였다. 마지막으로 실제 칩에 적용 되는 솔더 범프를 형성하여 플립칩 어셈블리 및 전기적 테스트를 수행하여, Solder droplet jetting이 실제 차세대 플립칩용 솔더 범프 형성 방법으로서 적용될 수 있음을 고찰하였다.

• 한국분무공학회지
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• 제21권1호
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• pp.53-57
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• 2016

The present study aims to experimentally investigate the evaporative heat transfer characteristics of Oxi-nitriding SPCC surface. Moreover, the heat transfer coefficient was examined with respect to surface temperature during droplet evaporation. In fact, the nitriding surface showed significant enhancement for anticorrosion performance compared to bare SPCC surface but the thermal resistance also increased due to the formation of compound layer. From the experimental results, the evaporative behavior of sessile droplet on nitriding surface showed similar tendency with the bare surface. Total evaporation time of sessile droplet on the nitriding surface was delayed less than 5%. The difference in heat transfer coefficient increased with the surface temperature, and the maximum difference was estimated to be around 11% at $80^{\circ}C$ surface. Thus, this nitriding surface treatment method could be useful for seawater heat exchanger industries.

• 한국분무공학회지
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• 제26권2호
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• pp.73-80
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• 2021

Evaporation characteristics of single butanol gel fuel were investigated in different mass ratios of gellant and ambient temperatures. Gel fuel was made by adding the pure water and hydroxypropylmethyl cellulose (HPMC) into the 1-butanol. Increase of viscosity was observed when the loading of HPMC increased. The evaporation process of gel droplet could be divided into three stages: droplet heating, micro-explosion and crust formation. Elevation of ambient temperature helped boost the evaporation in all experimental cases, but the effect was mitigated when the mass ratio of HPMC increased. Increase of HPMC weight ratio reduced the evaporation rate.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.2-5
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• 2008

This study describes the numerical simulation of three-dimensional droplet formation and the following motion in a cross-junction microchannel by using the Lattice Boltzmann Method (LBM). Our aim is to develop the three-dimensional binary fluids model, consisting of two sets of distribution functions to represent the total fluid density and the density difference, which introduces the repulsive interaction consistent with a free-energy function between two fluids. We validated the LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we applied our code to the numerical simulation of a binary fluid flow in a cross-junction channel focusing on the investigation of the droplet formulation. Due to the pressure and interfacial-tension effect, one component of the fluids which is injected from one inlet is cut off into many droplets periodically by the other component which is injected from the other inlets. We considered the effect of the boundary conditions for density difference (order parameter) on the wetting of the droplet to the side walls.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.559-564
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• 2008

A prediction of binary droplets collision is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter and drop-size ratio have influence on the interaction of the droplets. By the effect of these parameter, the collision processes are generated with the complicated phenomena. The droplet collision can be classified into four interactions such as the bouncing, coalescence, reflexive separation and stretching separation. In this study, the two-phase flow of the droplet collision was simulated numerically by using the Level Set method. 2D axi-symmetric simulations on the head-on collisions in the coalescence and reflexive separation, and 3D simulation on the off-center collisions in the coalescence and stretching separation were performed. These numerical results showed good agreements with the experimental and analytical results. For tracking the identity of droplets after the collision, transport equation for the volume fraction of the each initial droplet were used. From this, the identities of droplets were analyzed on the collision of droplets having different size.

• Asian Journal of Atmospheric Environment
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• 제5권1호
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• pp.56-63
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• 2011

Quantifying the solute composition of a cloud droplet (or a whole droplet) is an important task for understanding formation processes and heating/cooling rates. In this study, a combination of droplet fixation and SR-XRF microprobe analysis was used to visualize and quantify elements in a micro-scale droplet. In this study, we report the preliminary outcome of this experiment. A spherical micro-scale droplet was successfully solidified through exposure to ${\alpha}$-cyano-acrylate vapor without affecting its size or shape. An X-ray microprobe system equipped at the beam line 37XU of Super Photon ring 8 GeV (SPring-8) was applied to visualize and quantify the elemental composition in an individual micro-scale droplet. It was possible to reconstruct 2D elemental maps for the K and Cl contained in a microdroplet that was dispensed from the 10-ppm KCl standard solution. Multi-elemental peaks corresponding to X-ray energy were also successfully resolved. Further experiments to determine quantitative measures of elemental mass in individual droplets and high-resolution X-ray microtomography (i.e., 3D elemental distribution) are planned for the future.

• 반도체디스플레이기술학회지
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• 제20권3호
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• pp.51-56
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• 2021

Using an inkjet printing process, we have investigated a droplet formation of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) near the orifice of a piezoelectric inkjet head. With an attempt to form the smallest droplet without any satellites, we have applied various waveforms such as the unipolar, bipolar, and M-shaped waveforms. It is found that the droplet velocity and volume vary depending sensitively on the waveform width and voltage. Of those, the M-shaped waveform is shown to provide the smallest droplet volume, followed by the bipolar and then unipolar waveforms. The droplet printed on a PET film roll by the M-shaped waveform has the diameter as small as 46.1 ㎛. It is likely that the second short unipolar in the M-shape waveform increases the droplet velocity gradient, rendering the droplet smaller.