• Title/Summary/Keyword: 액적 거동

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Spreading Dynamics of an Ellipsoidal Drop Impacting on a Heated Substrate (고온으로 가열된 고체 표면과 충돌하는 타원형 액적의 퍼짐 거동)

  • Yun, Sungchan
    • 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.

Behavior of Liquid Droplet Driven by Capillarity Force Imbalance on Horizontal Surface Under Various Conditions (다양한 조건하에서 모세관력 불균형에 의해 구동되는 수평 표면 위의 액적 거동)

  • Myong, Hyon Kook;Kwon, Young Hoo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.4
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    • pp.359-370
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    • 2015
  • The present study aims to numerically investigate the behavior of liquid droplet driven by capillarity force imbalance on horizontal surfaces ranging from hydrophilic to hydrophobic, under various conditions. The droplet behavior has been simulated using an in-house solution code(PowerCFD), which employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The detailed droplet behavior was obtained under various conditions for droplets with different initial shapes, contact angles and surface tension forces(or Bond number). The mechanism of droplet transport was examined using the numerical results on the droplet shapes.

A Numerical Analysis of the Binary Droplet Collision by Using a Level Set Method (레벨셋 방법을 이용한 액적 충돌에 대한 수치해석)

  • Lee, Sang-Hyuk;Hur, Nahm-Keon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.4
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    • pp.353-360
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    • 2011
  • The prediction of binary droplet collisions is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter, and drop-size ratio influence the interaction between the droplets. The effect of these parameters results in complicated collision phenomena. Droplet collisions can be classified into four types of interactions: bouncing, coalescence, reflexive separation, and stretching separation. In the present study, the interfacial flow problem of the droplet collision was numerically simulated by using the level set method. 2D axisymmetric simulations on the head-on collisions and 3D simulation on the off-center collisions were performed. The numerical results of droplet behavior after the collision agreed well with the experimental and analytical results. The mixing of the mass of the initial droplets after the collision was also predicted by using different species index of colliding droplets.

Eulerian-based Numerical Modeling for Impingement Prediction of Supercooled Large Droplets (과냉각대형액적 충돌예측을 위한 오일러리안 기반 수치 모델링)

  • Jung, Sung-Ki;Kim, Ji-Hong
    • 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.

Dissolution Behavior of Liquid CO2 Injected into the Ocean at the Untermediate Depth (중층심해에 분사된 액체 이산화탄소의 용해거동에 관한 연구)

  • 김남진;강종호;이재용;김종보
    • Journal of Energy Engineering
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    • v.9 no.1
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    • pp.41-46
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    • 2000
  • 인류가 발생시키는 이산화탄소를 액화시켜 해양에 저장 또는 용해시키는 방법이 지구온나화 현상을 완화시키는 기술로 알려져있으며, 이 방법을 발전시키기위해서는 심해에 분사된 이산화탄소 액적의 용해거동을 정확히 예측하여야한다. 본 연구에서 중층심해 1000m와 1500m 깊이에 분사된 액체 이산화탄소 액적의 용해거동을 계산한 결과, 해저 약 4500m 깊이에서 이산화탄소의 밀도와 용해도가 가장 크게 변하였고, 분사된 이산화탄소는 초기 액적 지름이 각각 0.010m 그리고 0.015m 이하일 때 500m 이하의 깊이에서 완전히 용해되었다. 그리고 해수와 액체 이산화탄소의 접촉면에 생성되는 하이드레이트막이 이산환탄소 용해에 장애물로 작용한다는 것을 확인하였다.

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Effects of Convective Velocity and Ambient Pressure on the Characteristics of Heptane Droplet Vaporization in Supercritical Environments (초임계상태에서 주위 유동 속도와 압력 변화에 따른 헵탄 액적의 기화 특성)

  • Lim, Jong-Hyuk;Lee, Bong-Su;Koo, Ja-Ye
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.4
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    • pp.71-78
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    • 2005
  • The vaporization characteristics of a liquid heptane droplet in a supercritical nitrogen flow is numerically analyzed. The present model can account for real gas effects, liquid-phase internal circulation, variable thermodynamic properties and high-pressure effects. Time marching method with preconditioning scheme is employed to handle the low Mach number flows in dense heptane droplet region. Computations are made for the wide range of convective velocity and ambient pressure. Numerical results indicate that the droplet deformation becomes stronger by increasing the Reynolds number and it becomes relatively weak by increasing the pressure.

Buzz Characteristic of Supersonic Propulsion System with Spray Injection and Combustion (액적 분사/연소를 고려한 초음속 엔진의 buzz 특성)

  • Kim, Seong-Jin;Yeom, Hyo-Won;Sung, Hong-Gye;Gil, Hyun-Yong;Yoon, Hyun-Gull
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.05a
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    • pp.411-414
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    • 2010
  • In supersonic propulsion system, the inlet buzz phenomenon in the subcritical operation arises large pressure oscillation, combustion instability, and thrust loss, etc. Inlet Buzz phenomenon and the spray injection/combustion are figured out by the unified unsteady numerical analysis. TAB(Taylor Analogy Breakup) model was applied. Acoustic mode of the entire engine was investigated by detail analysis of pressure fluctuation at each location of the engine.

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Experimental Study on the Soot Formation Behavior of Octane Single Fuel Droplet Under the Constant Volume Combustion Conditions (정적 연소 조건에서 Octane 단일 연료 액적의 매연 생성 거동에 관한 연구)

  • Lim, Young Chan;Suh, Hyun Kyu
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.6
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    • pp.389-395
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    • 2017
  • This study was performed to provide the information of the soot formation behavior of octane single fuel droplet under the identical combustion conditions. To achieve this, this experimental study provide the results of the soot formation characteristics of octane droplet in accordance with different initial droplet diameter($d_0$), at the same time, experiment was conducted under the same combustion conditions which are 1.0atm of ambient pressure($P_{amb}$), 21% of oxygen concentration($O_2$) and 79% of nitrogen concentration($N_2$). Visualization of octane droplet combustion was performed by visualization system with high speed camera. The results of maximum soot volume fraction($f_{vmax}$) was almost the same under the equivalent ambient conditions regardless of initial droplet diameter. Furthermore, maximum soot volume fraction was showed the higher value in the measuring direction between $135^{\circ}$ and $315^{\circ}$ since the soot-tail is generated during two opposing igniters movement process.

RADIAL FLOW AND DROPLETS SPLASH OBSERVED ON A WALL IMPINGEMENT JET (벽면 충돌분무의 반경방향 흐름과 액적 비산에 관한 고찰)

  • KIM, Young-Il
    • Journal of the Korean Society of Industry Convergence
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    • v.3 no.1
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    • pp.37-42
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    • 2000
  • 액체 분무가 벽면의 평평한 면에 충돌할 때의 거동에 대해 실험을 통하여 조사하였다. 각 분사노즐과 벽면까지의 거리 그리고 분사 속도에 있어서 충돌점에서의 액체 액막의 비산 거동과 평면에서의 액막의 흐름에 대하여 관찰하였다. 충돌점에서 비산하는 액적의 비산율을 정량적으로 측정하였다. 분사속도가 증가에 의해 충돌 거동은 5개의 영역으로 분류되며, 분사속도가 증가하면 비산율도 증가하게 된다. 또한, 충돌거리가 분무의 분열점보다 길때의 분사량의 약 반 정도가 비산하게 되는 결과가 얻어졌다.

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Size and Rising Velocity of Liquid Drops in Liquid-Liquid Fluidized-Bed Extractors (유동층 액-액 추출기에서 액적의 크기 및 상승속도)

  • Jung, Sung-Hyun;Kim, Jae-Han;Kang, Tae-Gyu;Kang, Yong;Kim, Sang Done
    • Applied Chemistry for Engineering
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    • v.16 no.1
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    • pp.34-38
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    • 2005
  • Characteristics of size, rising velocity and distribution of liquid drops have been investigated in a immiscible liquid-liquid fluidized-bed whose diameter was 0.102 m and 2.5 m in height. Effects of velocities of dispersed (0~0.04 m/s) and continuous (0.02~0.14 m/s) liquid phases and fluidized particle size (1, 2.1, 3 or 6 mm) on the liquid drop properties in the extractor have been determined. The resultant flow behavior of liquid drops became more complicated with increasing the velocity of dispersed or continuous liquid phase. The resultant flow behavior of liquid complicated with increasing the velocity of dispersed or continuous liquid phase. The resultant flow behavior of liquid drops depended strongly upon the drop size and its distribution. The drop size increased with increasing dispersed phase velocity, but decreased with increasing particle size. However, the size of liquid drop exhibited a local maximum with increasing continuous liquid velocity. The size and rising velocity of liquid drops have been well correlated in terms of operating parameters.