• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.5
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• pp.68-74
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• 2015

In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.114-122
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• 2015

In the high convective gas flow condition, irregular shaped water waves from which droplet entrainment occurs are generated under horizontally stratified two-phase flow condition. KAERI proposed a new mechanistic droplet entrainment model based on the momentum balance equation consisting of the shear stress, surface tension, and gravity forces. However, this model requires correlation or experimental data of several physical parameters related to the wave characteristics. In the present study, we tried to measure the physical parameters such as wave slope, wave hypotenuse length, wave velocity, wave frequency, and wavelength experimentally. For this, an experiment was conducted in the horizontal rectangular channel of which width, height, and length are, respectively, 40 mm, 50 mm, and 4.2 m. In the present test, the working fluids are chosen as air and water. The PIV technique was applied not only to obtain images for phase interface waves but also to measure the velocity field of the water flow. Additionally, we developed the parallel wire conductance probe for the confirmation of wave height from PIV image. Finally, we measured the physical parameters to be used in the validation of new droplet entrainment model.

• Journal of Energy Engineering
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• v.4 no.3
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• pp.394-401
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• 1995

본 연구는 중심부에 액체, 외주부에 산화제가 흐르는 기액 동축분류의 유동장에 대한 것이다. 기액 동축 분사기는 연료의 분사량이 적은 소형 연소시스템을 고려하여, 실험은 연공비(W1/Wa)가 0.6 이하를 대상으로, 물과 공기를 사용하여 분사조건에 따른 분무특성과 기액 2상 분무류의 기본구조를 조사하여 액적의 확산, 기액혼합특성에 대하여 검토하여 다음과 같은 결론을 얻었다. 반경방향 기상속도분포 및 액적유속분포는 분구직경 및 분사조건에 관계없이 정규분포에 가까운 형태를 취하고 있으며, 각각 식 (2) 및 (3)으로 나타낼 수 있다. 기상속도는 반치폭은 축방향에 따라 일정한 구배 (≒4.6)로서 증가하며, 기상만의 단상분류의 구배(≒6)에 비해서 완만하다. 액적유속 반치폭은 축방향에 따라 더욱 완만한 구배(≒3.1)로서 증가한다. 무차원 액적유속분포는 축방향에 따라 일정한 구배(n≒1.5)로서 감소한다. 액적의 확산은 상대적으로 기액유량비가 클수록 효과적으라고는 말할 수 없고, 최대 확산을 이루는 최적의 기액유량비가 존재한다.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.2
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• pp.1-9
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• 2010

LES(Large eddy simulation) of breakup and droplet atomization of a liquid jet into cross turbulent flow was performed. Two phase flow of gas and liquid phases were modeled by the mixed numerical scheme of both Eulerian and Lagrangian methods for gas and liquid droplet respectively. The breakup process of a liquid column and droplets was observed by implementing the blob-KH wave breakup model. The penetration depth into cross flow was comparable with experimental data for several variants of the liquid-gas momentum flux ratio by varying liquid injection velocity. SMD(Sauter Mean Diameter) distribution downstream of jet was analyzed.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.2
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• pp.15-22
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• 1988

실제의 흡기관에서는 단면이 일정한 직관이 아니며, 피스톤기관의 흡기관은 단면변화가 불가피하여 액적은 소성으로 인한 관벽과의 충돌로 부착하게 되고 액적부유율은 더욱 작게 된다는 D.A. Trayser, W.E. Ranz등의 보고가 있다. 또 보제행남들은 액막류의 발생이 유해배기 가스를 증가시키고 액막류의 감소는 기통사이의 연료분배의 불균일도를 저하시키므로 NOx, HC, CO가 크게 감소된다고 보고하였다. 이와같이 액막유의 존재는 각 실린더에 유입하는 연료의 질적차이를 가져오기 때문에 액막유를 분리제거하는 방법의 연구도 많이 이루어지고 있으나 아직 실용상에 문제가 많은 것으로 남아있다. 따라서 본 고에서는 이와같이 문제되고 있는 흡기관내 액막유동의 거동을 고찰하기 위하여 액막두께 변동을 측정하는 방법에 대하여 저자들이 사용하였던 방법과 그외 초음파를 이용한 액막두께 측정법을 소개하고자 한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.1-8
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• 2009

Present studies of these experiments was conducted to using water, over a range of cross-flow velocities from 42 to 136 m/s, with injection frequencies from 35.7 to 166.2 Hz. In cross-flow field, main parameters of liquid jet for secondary breakup were cross-flow drag rather than pressure pulse frequency. As oscillation of the periodic pressure, liquid jet was moved up and down. Also, a bulk of liquid jet puff was detected at upper field of liquid surface. Because of pressure pulsation frequency, an inclination of SMD for the structured layer was evanescent. Cross-sectional characteristics of SMD at downstream area were non-structured distributions. The tendency of volume flux value for various frequency of pressure pulse was same distribution. And volume flux was decreased when the frequency of pressure pulse increasing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.290-297
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• 2016

A two-phase Large Eddy Simulation(LES) has been conducted to investigate breakup and atomization of a liquid jet in a cross turbulent flow in a rectangular duct. Gas-droplet two-phase flow was solved by a coupled Eulerian-Lagrangian method which tracks every individual particles. Effects of liquid breakup models, sub-grid scale models, and a order of spatial discretization was investigated. The penetration depth in cross flow was comparable with experimental data by varying breakup model and LES scheme. SMD(Sauter Mean Diameter) distribution downstream of jet was analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.48-58
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• 2006

The spray and combustion characteristics of liquid jet in cross flow with variation of injection angle are numerically studied. Numerical analysis was carried out using KIVA code, which may be used to generate numerical solutions to spray and chemical reactive fluid problem in three space dimensions and modified to be suitable for simulating liquid jet ejected into the cross flow. Wave model and Kelvin- Helmholtz(KH) /Rayleigh-Taylor(RT) hybrid model were used for the purpose of analyzing liquid column, ligament, and the breakup of droplet. Penetration length increases as flow velocity decreases and injection velocity increases. Numerical error increases as inflow velocity increases. The results of flame propagation contour in combustion chamber and local temperature distribution, combustion emissions were obtained.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.933-942
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• 1992

The effects of the folwrate on the dropsize from the two-phase coaxial nozzle are investigated by using the direct photographic method and the empirical equation is obtained. For the photography, the light source which the life time is the order of 100ns is fabricated and the lens is the zoom lens which has the MICRO function with a teleconvertor. The distillated water and the compressed air of the surrounding temperature are injected and atomized. For the purpose of the exact adjustment and measurement of the flowrates, the two rotameters are used. As a result of this study, the sauter mean diameter of droplets has a tendency for a logarithmic function with air flowrate and for a exponential function with water flowrate.