• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.98-103
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• 2002

초음파 비가진 시인 상용분무와 초음파가진 시인 개질분무, 간접진동분무, 간접진동 및 개질의 겸용분무의 네가지 경우 모두에서 분무액적의 평균직경 및 SMD가 전 영역에 걸쳐서 노즐 글에서 분무방향으로 멀어질수록 조금씩 증가했으며, 또한 초음파 비 가진시인 상용분무 경우가 초음파 가진 세경우에 비해 크게 나타났다. 초음파 가진 세가지 경우에서는 간접진동 및 개질법 겸용의 경우에서 분무액적의 미세화가 가장 우세하게 나타났다. 이는 초음파가 분무 축방향 전영역에 걸쳐서 분무액적의 미세화에 친화적임을 입증한다. 나. 분무 방향 축에서 반경 방향으로 갈수록 분무 액적의 평균 직경과 SMD는 감소하고 있으며, 반경방향 전 영역에 걸쳐서 상용 분무시의 액적이 가장 크게, 초음파겸용 경우에서 가장 작게 나타나고 있다. 이는 초음파가 분무 내부 전 영역에 걸쳐 액적의 미세화에 친화적임을 증명한다. 다. 분무액적의 크기에 따른 분무 분포도 비교에서 네가지 경우 모두에서 축 방향 거리가 멀수록 분무액적의 크기가 다소 증가함을 보였고, 축에서 반경 방향으로는 분무액적의 크기가 다소 감소함을 보이고 있다. 상용 분무와 초음파 분무의 비교에서 초음파 겸용 가진시는 상용 분무 때 보다 분무 영역 전반에 걸쳐서 미세화가 뚜렷이 우세함을 보였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.201-206
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• 2005

The effect of internal liquid flow on spray plume characteristics was performed experimentally in subsonic crossflows. The injector internal flow was classified as three modes such as a normal, cavitation, and hydraulic flip. The objectives of the research are to investigate the effect of internal liquid flow on the spray plume characteristics and compare the trajectory of spray plume with previous works. The results suggest that the trajectory of spray plume can be correlated as a function of liquid/air momentum flux ratio(q), injector diameter and normalized distance from the injector exit(x/d). It's also found that the injector internal turbulence influences the spray plume characteristics significantly.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.05b
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• pp.397-398
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• 2003

대기 중 분진을 제거하는 방식으로 여과 이론을 적용할 수 있는 경우는 섬유 여과기, 입자상 여과기, 액적에 의한 습식 세정기 그리고 기포를 이용한 분진 제거 방법 등을 들 수 있다. 이러한 여과 원리를 이용한 집진 설비를 설계하는데 있어, 액적 또는 기포 주위의 유동장을 정확히 파악하는 것은 매우 중요하다. 특히, 포집구의 크기가 작아지고 화학적으로 반응성을 갖는 고온의 함진가스가 유입되는 경우 및 저압에서 운영되는 경우에 누드센수(Knudsen number)의 영향을 무시할 수 없는데 이러한 영역을 저 누드센 영역(low Kundsen number regime)이라고 한다(Lee et al., 1978). (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.647-654
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• 2012

Supercooled large droplet issues in aircraft icing have been continually reported due to the important safety considerations. In order to simulate the impingement behavior of large droplets, a two-dimensional and compressible Navier-Stokes code was developed to determine the flow field around the test model. Also, the Eulerian-based droplet impingement model including a semi-empirical approach for the droplet-wall interaction process and droplet break-up was developed. In particular, the droplet-wall interactions were considered as numerical boundary conditions for the droplet impingement simulation in the supercooled large droplet conditions. Finally, the present results were compared with the experimental test data and the LEWICE results. The droplet impingement area and maximum collection efficiency values between present results and wind tunnel data were in good agreements. Otherwise, the inclination of collection efficiency of the present result is over-predicted than the wind tunnel data around a lower surface of the NACA 23012 airfoil.

• Fire Science and Engineering
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• v.13 no.1
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• pp.37-47
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• 1999

The spreading fire of very small floating particles after they are ignited is fast and t therefore dangerous. The research on this area has been limited to experiments and global simulations which treat them as dusts or gaseous fuel with certain concentration well m mixed with air. This research attempted micro-scale analysis of ignition of those particles modeling them as liquid droplets. For the beginning, the in-line array of fuel droplets is modeled by two-dimensional, unsteady conservation equations for mass, momentum, energy and species transport in the gas phase and an unsteady energy equation in the liquid phase. They are solved numerically in a generalized non-orthogonal coordinate. The single step chemical reaction with reaction rate controlled by Arrhenius’ law is assumed to a assess chemical reaction numerically. The calculated results show the variation of temperature and the concentration profile with time during evaporation and ignition process. Surrounding oxygen starts to mix with evaporating fuel vapor from the droplet. When the ignition condition is met, the exothermic reactions of the premixed gas initiate a and burn intensely. The maximum temperature position gradually approaches the droplet surface and maximum temperature increases rapidly following the ignition. The fuel and oxygen concentration distributions have minimum points near the peak temperature position. Therefore the moment of ignition seems to have a premixed-flame aspect. After this very short transient period minimum points are observed in the oxygen and fuel d distributions and the diffusion flame is established. The distance between droplets is an important parameter. Starting from far-away apart, when the distance between droplets decreases, the ignition-delay time decreases meaning faster ignition. When they are close and after the ignition, the maximum temperature moves away from the center line of the in-line array. It means that the oxygen at the center line is consumed rapidly and further supply is blocked by the flame. The study helped the understanding of the ignition of d droplet array and opened the possibility of further research.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.3
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• pp.205-209
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• 2017

Unlike spherical drop impact, ellipsoidal drop impact can control the bouncing height on a heated surface by significantly altering impact behavior. To scrutinize the effect of the aspect ratio (AR) of the drop on the bounce suppression, in this study, non-axisymmetric spreading behaviors are observed from two side views and characterized based on the spreading width of the drop for horizontal principal axes. In addition, the maximum spreading width is investigated for various ARs. The results show that as the AR increases, the maximum spreading width of the minor axis increases, whereas that of the major axis shows no significant variation. In the regime of high AR and high impact velocity, liquid fragmentations by three parts are observed during bouncing. These fragmentations are discussed in this work. The hydrodynamic features of ellipsoidal drop impact will help understand bouncing control on non-wetting surfaces for several applications, such as self-cleaning and spray cooling.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2067-2072
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• 2007

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, as an initial step, the wall impact of an electrically charged droplet has been experimentally investigated. The charged drops were directed on the surface of a paraffin wax, and the impinging behavior was visualized and recorded using a CCD camera to identify the impingement regime. The spread-rebound boundary for the charged drop turned out to be smaller compared to that for an electrically neutral droplet under the same surface condition. The shift of the transition criterion is considered to be due to the discrepancy between the maximum spread ratio of the electrically charged droplet and that of the neutral droplet.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2995-3000
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• 2008

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, the wall impact behavior of an electrically charged drop has been investigated and compared with that of a neutral drop experimentally. The critical Sommerfeld number representing the spread-splash boundary for the charged drop impacting on the dielectric substrate turned out to be larger compared to that for the neutral drop with the same surface condition. The change of the transition boundary is due to the increase in the surface wettability of the drop on the substrate. However, with the electrically conducting substrates, the charging effect on the transition boundary appeared negligible. This is because the electric discharging time is much shorter than the time required for the flattened drop to reach its maximum extent.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.59-63
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• 2006

A direct photograph measurement technique was used to determine the spatial distribution of the spray droplet diameter in subsonic crossflow and it also obtain that SMD distribution by using PLLIF technique. The injector internal flow was classified as three modes such as a normal, cavitation, and hydraulic flip. The objectives of this research are getting a droplet distribution and drop size measurement of normal flow and compare with the other flow effects. Although the study showed visually that drop size were spatially dependent of Air-stream velocity, fuel injection velocity, and normalized distance from the injector exit length.(x/d, y/d) There are also difference characteristics between cavitation, hydraulic flip and the normal flow.