• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.1
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• pp.28-38
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• 2009

Numerical simulation is performed for microdroplet deposition on a pre-patterned micro-structure. The liquid-air interface is tracked by a level-set method, which is improved by incorporating a sharp-interface modeling technique for accurately enforcing the matching conditions at the liquid-gas interface and the no-slip condition at the fluid-solid interface. The method is further extended to treat the contact angle condition at an immersed solid surface. The present computation of a patterning process using microdroplet ejection demonstrates that the multiphase characteristics between the liquid-gas-solid phases can be used to improve the patterning accuracy.

• Fire Science and Engineering
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• v.29 no.5
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• pp.29-33
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• 2015

In this study, the relations of flow rate, discharging distance and droplet size are measured in accordance with the nozzle shape. The dual type nozzles of LPN142 and LPN148, which have identical core diameter (6.0 mm) and the different radial injection angles (${\theta}_2=142^{\circ}$ and $148^{\circ}$), are manufactured. The distribution diameters with discharging distance are quantified by UL2167 test standard. The relations between discharging angle and droplet sizes, which are measured by the method of Helium-Neon laser equipment, are obtained by the empirical correlation as working pressure increase. Moreover, the extinction coefficient, which is major parameter of the radiative transport equation (RTE) is analyzed with variable droplet sizes. Thus, it is possible to opt the nozzle's shape by analyzing the relations of working pressure, spray distance, droplet size and fire characteristics at minimum allowable flow rate.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.19-26
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• 2022

In droplet microfluidics, precise droplet manipulation is required in numerous applications. This study presents ultrasonic surface acoustic wave (USAW)-based microfluidic device for label-free droplet separation based on size. The proposed device is composed of a slanted-finger interdigital transducer on a piezoelectric substrate and a polydimethylsiloxane microchannel placed on the substrate. The microchannel is aligned in the cross-type configuration where the USAWs propagate in a perpendicular direction to the flow in the microchannel. When droplets are exposed to an acoustic field, they experience the USAW-induced acoustic radiation force (ARF), whose magnitude varies depending on the droplet size. We modeled the USAW-induced ARF based on ray acoustics and conducted a series of experiments to separate different-sized droplets. We found that the experimental results were in good agreement with the theoretical estimation. We believe that the proposed method will serve as a promising tool for size-based droplet separation in a label-free manner.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2005.11a
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• pp.488-490
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• 2005

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.40 no.11
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• pp.18-24
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• 2011

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.6 s.261
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• pp.558-565
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• 2007

Many studies of microdroplet evaporation from solid surfaces were made with priority given to inkjet printing and dye painting techniques. The objective of these studies is how to evaporate a droplet quickly and uniformly. Also it is necessary to prevent evaporation of a droplet to observe cells in a droplet generated through cell-patterning. In general, an identical volume of a water droplet on hydrophobic surfaces evaporates slower than that on hydrophilic surfaces. In this study, we observe the evaporation process of a droplet on various hydrophobic surfaces and calculated the evaporation rate considering the droplet geometry such as contact angle and height. This study also proposes a new model based on the fact that evaporation mode at the edge of a droplet is different from that at the outer surface of a droplet as the contact angle changes during evaporation. Finally, we reveal the cause fur the increase of evaporation flux and show that the ratio of edge evaporation to total evaporation increases with time.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2159-2168
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• 1992

Coal-water slurry is considered to have the potential for displacing petroleum used in the existing oil-fired industrial and utility boilers. The combustion of coal-water slurry(CWS) is a complex process and little is known about the detailed mechanism. In this paper the combustion behavior of a single suspended droplet of CWS in hot gas stream was investigated. The effect of coal particle size, water content in droplet, initial droplet size, ambient temperature and oxygen fraction in ambient gas were studied. The results are as follows; (1) Increasing the oxygen fraction in ambient gas considerably reduced the char combustion time. (2) The variation of water content and coal particle size in droplet showed little effect on the combustion behavior. (3) In the relatively high temperature ambient gas, the water evaporation time became shorter and the combustion process was stable.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1550-1551
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• 2007

노즐 직경 $30\;{\mu}$인 MEMS 압전 잉크젯 헤드를 이용하여 Ag 나노 잉크를 PDMS 처리된 PI(Polyimide) 기판 위에 토출하였다. 구동주파수 5 KHz에서 액적부피 1.5 pl, 속도가 약 4.5 m/s인 액적이 토출 되었다. 인쇄된 액적의 크기는 직경 약 $12\;{\mu}m$이었다. 메니스커스의 거동에 맞춘 구동파형의 입력에 의해 새틀라이트 없는 매우 작은 액적을 토출할 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.106-106
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• 2004

보일러에서 연소된 후 배출된 가스는 탈황목적으로 설치된 흡수탑 내에 유입되어 Slurry Spray Nozzle에서 분사된 Limestone Slurry에 의해 배기가스중의 SO$_2$를 흡수한 다음 반응조로 떨어지게 되지만 분사된 액적의 일부는 배기가스의 압력에 의하여 같은 유동 방향으로 미세한 Mist의 형태로 배기가스와 함께 흡수탑의 Outlet Duct를 통해 빠져나간다. 이 Mist(액적크기 40 $\mu\textrm{m}$이하)에는 고형 성분이 함유되어 있는데 보통 Chloride농도가 높아 탈황설비 후단 (duct, GGH, Stack)에 plugging, 부식 등의 문제를 유발하므로 Spray Header상부에서 Mist Eliminator를 설치하여 Mist를 제거하도록 한다.(중략)

• Journal of ILASS-Korea
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• v.11 no.2
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• pp.98-104
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• 2006

A charged droplet scrubber was introduced to remove visible smokes generated in many industrial facilities. Lab-scale and field tests were conducted in this study. The system consists of a corona discharger to effectively charge the fine particles, fellowed by an electrostatic chamber to promote coagulation between charged fine particles and oppositely charged droplets and a demister to remove resultant particles. Overall collection efficiency, 98.4% was obtained from a lab-scale test, when a high voltage was applied to an ionizer and a charged droplet scrubber. Field tests also show the high collection efficiencies, 93.5% with one stage and 99.4% with two stage system. This system can be used to increase the collection efficiency of the conventional air pollution control devices to satisfy the national emission standard.