• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.255-267
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• 2020

Under SLD conditions, due to the large size of droplets, physical phenomena such as wall-droplet interaction and deformation have a significant effect on the icing process. Accordingly, many studies have been conducted in order to computationally simulate SLD effects. As one of the efforts, post-processing method have been proposed to describe wall-droplet interaction effect, which modified collection efficiency using Wright model. However, since the model doesn't properly consider the wall condition, it still overestimated collection efficiency and impingement limit. To solve this problem, impingement areas were divided into 3 different regions, and the post-processing method was introduced with the new wall-droplet interaction model developed based on Bai and Gosman rebound model. In order to consider the effect of deformation, the most suitable model was selected by comparing the deformation models used in the various icing codes. As a result, the modified post-processing method showed improved accuracy in predicting the impingement limits and collection efficiency by further estimating mass flux loss due to rebound, and it was observed that the result was the closest to the experimental data when the deformation effect was included by using Wiegand model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.179-179
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• 2006

산업기술의 고도화에 따른 IT 산업의 급속한 발전으로 각종 전자, 정보통신기기에 대해 더욱 소형화 고성능화를 요구하고 있다. 이와 같은 경향에 따라 더욱 향상된 기능을 가지고 각종 소자 부품의 개발과 동시에 유독 물질 발생이 없는 청정생산기술 개발에 대한 요구가 끊임없이 제기 되어 왔다. 이러한 요구에 부응하여 기술들이 개발되고 있으며 그 중의 하나로 잉크젯 프린팅 기술이 연구되고 있다. 특히 Dod(Drop on Demand) 방식의 잉크젯은 가정용 프린터로 개발되어 널리 보급된 기술이지만, 이 기술을 PCB 제조기술에 전용하면 친환경 생산공정으로 부품 성장밀도를 증대 시킬 수 있다. 기존의 PCB 제조기술은 전극과 신호 패턴을 형성시키기 위하여 노광공정과 에칭공정을 반복적으로 사용하고 있는데, 노광공정에서 쓰이는 마스크와 유틸리티 설비 유지 비용의 문제가 대두되고 있다. 노즐로부터 분사된 잉크 액적들의 집합으로 기판위에 점/선/면의 인쇄이미지를 구현하게 된다. 그러므로 인쇄 해상도는 잉크액적 및 인쇄 방법, 기판과의 상호작용에 크게 의존하게 된다. 잉크 액적과 기판의 상호작용에 영향을 미치는 요소로는 잉크의 물리화학적 물성(밀도, 점도, 표면장력), 잉크 액적의 충돌 조건(액적 지름, 부피, 속도), 그리고 기판의 특성(친수/소수성, Porous/Nonporous, 표면조도 등)을 들 수 있겠다. 우선적으로 노즐을 통과해서 분사되는 액적의 크기에 따라 기판위에 형성되는 라인의 두께 및 폭이 결정된다. 떨어진 액적이 기판위에서 퍼지는 것을 UV 조사를 통한 가경화 과정을 통해서 최종적으로 라인의 투께 및 폭을 조절하려고 한다. 따라서 선폭 $75{\mu}m$의 일정한 미세 배선을 형성시키기 위해 액적 크기 조절과 탄착 resist 액적 표면의 UV 가경화 조건으로 구현하려고 한다. 또한 DPI(Dot Per Inch) 조절을 통한 인쇄로 탄착 resist의 두께 확보 후 에칭시 박리되는 현상을 억제 시키려 한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.44-54
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• 2018

In a spray experiment using a venturi mounted on a lean premixed LPP injector, droplets appear to have non-uniform distributions. To solve this problem, the exit angle of the venturi was changed to form a dump surface on the nozzle neck. The dump surface improved the atomization performance and minimized droplet loss while forming recirculation zone in the venturi exit. In order to solve the non-uniform spray of the injector, the flow characteristics inside the venturi and SMD of the spray are compared. Finally, an optimum venturi shape is selected to minimize the spray loss and improve the spray performance.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.214-219
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• 2001

In this study, numerical investigation has been performed on the spreading and solidification of a droplet impacting onto a solid substrate in the thermal spray process. The finite difference method with volume-of-fluid approach is used to analyze the free surface flow and the source-based enthalpy method is employed to model the latent heat release during the solidification. In this work, the numerical model is validated through the comparison of the present numerical result with experimental data available for the flat substrate.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.109-114
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1597-1604
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• 2002

In this study, numerical investigation has been performed on the impingement, spreading and solidification of a coating material droplet impacting onto a solid substrate in the thermal spray process. The numerical model is validated through the comparison of the present numerical result with experimental data fer the flat substrate without surface defects. An analysis of deposition formation on the non-polished substrate with surface defects is also performed. The parametric study is conducted with various surface defect sizes and shapes to examine the effect of surface defects on the impact and solidification of the liquid droplet on the substrate.

• Journal of the Korean Society of Visualization
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• v.13 no.3
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• pp.20-23
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• 2015

In this experiment, a heterogeneous droplet consisted of de-ionized water and olive oil was made through two 31G injection needles. The injection flow rate was $50{\mu}{\ell}/min$ and the droplet size was 2 mm. The droplet was impinged onto a sapphire plate which was heated up to $300^{\circ}C$ by a heater. Two high speed cameras were used for visualization, and the frame rate was 20,000 fps. A 150W metal halite lamp was used for illumination. The dropping height was fixed to 20 mm and the corresponding Weber number was 10.6 based on water. Due to different boiling points of two liquids, partial boiling features of heterogeneous droplet was observed. At the Leidenfrost condition, micro explosion phenomenon has occurred.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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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.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.25-31
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP method. The result using improved CIP method shows the better result of the experiments, comparison with result of original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.180-186
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• 2012

A water-flow test for acceptance verification is carried out for a nonimpinging-type injector prior to the design-performance verification of 70 N-class liquid-rocket engine under development. It is observed that there exist varying characteristics of atomization among the injector-orifices caused by a fabrication crudeness of orifice holes which can be judged from a microscopic standpoint. The flow shedding phenomenon and ruffle on the surface of liquid column (or droplet) could be caught from the instantaneous spray images.