• 한국항공우주학회지
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• 제34권6호
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• pp.51-58
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• 2006

횡단 유동장내에서 일어나는 분무 현상에 대하여 분사각 변화에 대한 특성과 단일 노즐 형상에서 노즐의 크기와 길이에 대한 분무 특성을 연구하였다. 노즐은 단일 구멍으로 직경이 0.5 ㎜이고 노즐 대 노즐길이의 비(L/D)는 1.0에서 6.0이며 이미지는 고해상 줌 렌즈를 이용한 CCD 카메라를 통해 얻었으며, SMD와 액적의 속도는 PDPA와 상용 프로그램인 Image Express를 사용하였다. 액체 제트의 궤적은 웨버수와 모멘텀비, 노즐형상 변화(L/D)에 영향을 받아 액주가 후방으로 휘어지는 현상이 나타났다. 분사각이 낮을 때(${\theta}$ < $90^{\circ}$)에 노즐 형상보다는 웨버수 증가가 액체 제트의 궤적에 더 크게 영향을 미쳤으며, 분사각이 높을 때(${\theta}$ > $90^{\circ}$)에 노즐 형상 변화에 의한 분열점 변화가 액체 제트의 궤적에 더 크게 영향을 미쳤다.

• 한국분무공학회지
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• 제10권1호
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• pp.35-42
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• 2005

The present study has numerically and experimentally investigated the spray behavior of liquid jet injected in subsonic cross-flow. The corresponding spray characteristics are correlated with jet operating parameters. The spray dynamics are known to be distinctly different in the three regimes: the column, the ligament and the droplet regimes. The behaviors of column, penetration and breakup of liquid jet have been studied. Numerical and physical models are base on a modified KIVA code. The primary atomization is represented by a wave model base on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. In odor to capture the spray trajectory, CCD camera has been utilized. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio and the penetration decreases by increasing Weber number.

• 한국분무공학회지
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• 제13권4호
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• pp.187-192
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• 2008

In this study, the mechanisms of binary droplet collision were studied with diesel, ethanol and purified water. The droplet collisions of liquid droplet have been investigated for the same droplet diameter. In order to obtain the digital images of the droplet collision behavior, the experimental equipment was composed of the droplet generating system and the droplet visualization system. The droplets were produced by the vibrating orifice monodisperse generator. The visualization system consisted of a long distance microscope, a light source, and a high speed camera. The outcomes of binary droplet collision can be divided into four regimes, bouncing, coalescence, reflexive separation and stretching separation. The impact angle and the relative velocity of binary droplet are main parameters of collision phenomena, so the transition mechanism of droplet collision can be divided by the impact parameter.

• 대한기계학회논문집B
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• 제24권4호
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• pp.485-494
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• 2000

The purpose of this paper is to investigate a critical heat flux(CHF) during forced convective subcooled and saturated boiling in free water jet system impinged on a rectangular heated surface. The surface is supplied with subcooled or saturated water through a rectangular jet. Experimental parameters studied are a width of heated surface, a height of supplementary water and a degree of subcooling. Incipient boiling point is observed in the temperature of 6${\~}8^{\circ}C$ of superheat of test specimen. CHF depends on jet velocity for various boiling-involved coolant system. CHF also is proportional to the nozzle exit velocity to the power of n, where n is 0.55 and 0.8 for subcooled and saturated boiling, respectively. CHF is enhanced with a higher jet velocity, higher degree of subcooling and smaller width of a heated surface.

• 한국산업융합학회 논문집
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• 제7권1호
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• pp.5-11
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• 2004

벽면에 충돌하는 액체 분무의 충돌 거동과 액적 비산에 관하여 실험을 통하여 조사하였다. 액체 분무는 홀노즐에 의해 직경 40mm의 충돌판에 분사하게 된다. 액체 분무는 반경방향으로 퍼져나가 5개의 영역으로 분류되어 나타내게 된다. 난류 혹은 층류 분무의 경우, 충돌판에 충돌한 후 두꺼운 액막을 형성하게 되며, 이러한 상태에서 충돌하는 분무의 비산량은 매우 적으며 충돌 거리에 영향을 받지 않는다. 한편, 파동이 있는 분무의 충돌은 수력도약(Hydraulic jump)과 함께 반경방향으로 엷은 액막을 형성하게 되며 비산율도 증가하게 된다. 액체분무의 초속도가 증가하면 비산율도 증가하게 된다. 분열이 일어난 후에 충돌하는 파동 분무의 비산율은 분열이 일어나기 전에 비해 약 2~3배 정도 크게 나타난다. 비산율은 웨버수(Weber number)를 이용하여 요약할 수가 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.155-158
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• 2005

The spray characteristics of liquid jet minted in subsonic cross-flow were investigated numerically and experimentally. The behaviors of column, penetration and breakup of plain liquid jet in non-swirling cross-flow of air have been studied. Numerical and physical models are based on a modified KIVAII code. The primary atomization is represented by a wave model based on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. CCD camera has been utilized in oder to capture the spray trajectory. The nozzle diameter was 0.5 mm and its L/D ratios were between 1 and 5. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio, the penetration decreases by increasing Weber number and the turbulent or nonturbulent liquid jet is obtained at different L/D ratio.

• 한국분무공학회지
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• 제1권3호
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• pp.51-59
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• 1996

An experiment was carried out on the structure of twin spray from pressurize-swirl nozzles, in order to investigate the effect of different size of spray nozzles on the characteristics of the overlap of two single sprays, for example, mean diameter, number density, and spatial distribution of flow rate. Using image processing method, the distributions of size and velocity of droplets of a single spray and twin spray were measured and compared to investigate the overlapping effect of two identical sprays. Comparing experimental results from a twin-spray with those from two-single sprays shows that the flow rate distribution of the twin-spray was concentrated around the midst of the overlapping region of two sprays. In this region, Sauter mean diameter (SMD) did not change much in the twin spray from 6032 nozzles, but it was smaller by 10 micrometers in the twin-spray than two-single sprays from 60063 nozzles. In spite of large difference in Weber numbers of the colliding sprays between the 60063 and 6032 nozzles, the phenomena did not have a big change in the overlapping region of twin spray. This shows that in the collision between droplets from two single spray in the overlapping region to cause the disruption of droplets, the size distribution of spray droplets was also important as well as Weber number.

• 한국전산유체공학회지
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• 제15권4호
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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.

• 한국추진공학회지
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• 제16권5호
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• pp.1-9
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• 2012

동축형 다공성재 분사기에서는 중심 액체제트 주위를 둘러싼 원통형 다공성재의 내부 표면에서 반경방향으로 분사된 기체가 중심액체제트와 상호작용을 하게 된다. 표면분사된 기체제트는 반경방향에서 축방향으로 발달하며, 그 과정에서 액체분무의 중심부까지 운동량을 효과적으로 전달하여 미립화 및 혼합 성능을 향상시킨다. 본 연구에서는 기체분사 면적 및 기체분사 질량유량을 변화시켜 각각 운동량 비 및 웨버수의 크기를 조절하였으며, 이에 따른 물-공기 모사추진제 수류시험에서의 분무특성에 대한 고찰을 수행하고 동일 스케일의 전단 동축형 분사기와의 비교 분석이 이루어졌으며, 동축형 다공성재 분사기에서 반경방향으로의 기체분사가 2상유체의 미립화/혼합에 긍정적인 영향을 주는 것으로 판단된다.

• 한국추진공학회지
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• 제21권3호
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• pp.34-40
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• 2017

본 연구에서는 모사젤 추진제의 표면장력을 적환법(Du $No{\ddot{u}}y$ ring method)을 이용하여 측정하고 젤화제 및 금속입자 첨가량에 따른 표면장력 변화를 분석하였다. 금속입자 첨가에 따른 영향을 파악하기 위해 증류수를 기반유체로 그리고 젤화제는 Carbopol 941을 사용하였으며, 금속입자로는 평균입도 100 nm의 구형 스테인리스 304 입자를 사용하였다. 측정결과, 표면장력은 젤화제의 첨가량 증가에 따라 증가하였으나, 모사젤 추진제 내에 금속입자 첨가에 따른 표면장력은 다른 경향을 나타내었다.