• Title/Summary/Keyword: Weber number

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Experimental Investigation of Collision Mechanisms Between Binary Droplet of Fuel Jet (연료 제트의 두 액적간의 충돌기구에 관한 실험적 연구)

  • Lee, Keun-Hee;Kim, Sa-Yop;Lee, Chang-Sik
    • Journal of ILASS-Korea
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    • v.13 no.4
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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.

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Calculation of Fuel Spray Impingement and Fuel Film Formation in an HSDI Diesel Engine

  • Kyoungdoug Min;Kim, Manshik
    • Journal of Mechanical Science and Technology
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    • v.16 no.3
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    • pp.376-385
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    • 2002
  • Spray impingement and fuel film formation models with cavitation have been developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process was modeled by considering the effects of surface temperature conditions and fuel film formation. The behavior of fuel droplets after impingement was divided into rebound, spread and splash using the Weber number and parameter K(equation omitted). The spray impingement model accounts for mass conservation, energy conservation, and heat transfer to the impinging droplets. The fuel film formation model was developed by integrating the continuity, momentum, and energy equations along the direction of fuel film thickness. Zero dimensional cavitation model was adopted in order to consider the cavitation phenomena and to give reasonable initial conditions for spray injection. Numerical simulations of spray tip penetration, spray impingement patterns, and the mass of film-state fuel matched well with the experimental data. The spray impingement and fuel film formation models have been applied to study spray/wall impingement in high-speed direct injection diesel engines.

Critical Heat Flux of an Impinging Water Jet on a Heated Surface with Boiling (비등을 수반하는 발열면에 충돌하는 수분류의 임계열유속에 관한 연구)

  • Lee, Jong-Su;Kim, Heuy-Dong;Choi, Kuk-Kwang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.4
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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.

Dynamic Behavior of Heterogeneous Impinging Droplets onto High Temperature Plate (고온평판에 충돌하는 비균일혼합액적의 동적거동 특성)

  • Lee, Choong Hyun;Kim, Kyung Chun
    • Journal of the Korean Society of Visualization
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    • v.13 no.3
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    • pp.20-23
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    • 2015
  • In this experiment, a heterogeneous droplet consisted of de-ionized water and olive oil was made through two 31G injection needles. The injection flow rate was $50{\mu}{\ell}/min$ and the droplet size was 2 mm. The droplet was impinged onto a sapphire plate which was heated up to $300^{\circ}C$ by a heater. Two high speed cameras were used for visualization, and the frame rate was 20,000 fps. A 150W metal halite lamp was used for illumination. The dropping height was fixed to 20 mm and the corresponding Weber number was 10.6 based on water. Due to different boiling points of two liquids, partial boiling features of heterogeneous droplet was observed. At the Leidenfrost condition, micro explosion phenomenon has occurred.

A Study of Collision Model in Coaxial Swirl Injector (동축 스월형 분사기에서 충돌 모델 연구)

  • Moon, Yoon-Wan;Seol, Woo-Seok;Yoon, Young-Bin
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.320-323
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    • 2008
  • In this study the effect of collision model was evaluated in spray field by CFD. A collision is basically the interaction between droplets and criteria of collision is determined by drop Weber number, impact parameter, and drop-size ratio. Early developed collision model considered coalescence and grazing collision with the exchange of momentum. However in experimental research there were bouncing, coalescence, reflexive separating and stretching separating in interaction between droplets. In this study the collision considering such complex phenomena is modeled and was compared with the basic collision model.

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Simulation of Spray Impingement and Fuel Film Formation in a Direct Injection Diesel Engine (직접분사식 디젤엔진에서의 분무충돌과 연료액막형성 해석)

  • Kim, Man-Shik;Min, Kyoung-Doug;Kang, Bo-Seon
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.919-924
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    • 2000
  • Spray impingement model and fuel film formation model were developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process were modelled by considering the change of behaviour with surface temperature condition and fuel film formation. We divided behaviour of fuel droplets after impingement into stick, rebound and splash using Weber number and parameter K. Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. A fuel film formation model was developed by Integrating the continuity, the Navier-Stokes and the energy equations along the direction of fuel film thickness. The validation of the model was conducted using diesel spray experimental data and gasoline spray impingement experiment. In all cases, the prediction compared reasonably well with experimental results. Spray impingement model and fuel film formation model have been applied to a direct injection diesel engine combustion chamber.

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Effect of Internal Geometry of Nozzle on the Velocity and Droplet Size of Twin Spray (노즐이 내부형상이 이중분무의 유속과 입경에 미치는 영향)

  • Kim, Young-Jin;Jung, Ji-Won;Kim, Duck-Jool
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1522-1527
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    • 2004
  • The purpose of this study is to investigate the effect of swirler angle and swirl chamber aspect ration of nozzle on the characteristics of single and twin spray. The performances of nozzle has been investigated by measurements of spray angle, droplet size, velocity and Weber number at a water pressure 0.4MHz. Visualization of spray was conducted to obtain the spray angle and breakup process. The spray characteristics such as droplet size and velocity were measured by Phase Doppler Anemometry(PDA). It was found that the smaller swirler angle, the larger axial velocity became. It was also shown that the larger aspect ratio, the smaller droplet diameter became.

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Droplet size prediction model based on the upper limit log-normal distribution function in venturi scrubber

  • Lee, Sang Won;No, Hee Cheon
    • Nuclear Engineering and Technology
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    • v.51 no.5
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    • pp.1261-1271
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    • 2019
  • Droplet size and distribution are important parameters determining venturi scrubber performance. In this paper, we proposed physical models for a maximum stable droplet size prediction and upper limit log-normal (ULLN) distribution parameters. For the proposed maximum stable droplet size prediction model, a Eulerian-Lagrangian framework and a Reitz-Diwakar breakup model are solved simultaneously using CFD calculations to reflect the effect of multistage breakup and droplet acceleration. Then, two ULLN distribution parameters are suggested through best fitting the previously published experimental data. Results show that the proposed approach provides better predictions of maximum stable droplet diameter and Sauter mean diameter compared to existing simple empirical correlations including Boll, Nukiyama and Tanasawa. For more practical purpose, we developed the simple, one dimensional (1-D) calculation of Sauter mean diameter.

Direct Numerical Analysis of $CO_2$ degassing process in ${\mu}DMFC$ (마이크로 DMFC 에서 $CO_2$ degassing 과정의 직접 수치 해석)

  • Shin, Seung-Won;Shim, Jung-Ik;Wi, Wan-Seok;Jo, Sung-Won
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2648-2653
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    • 2007
  • Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

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NUMERICAL STUDY ON DROPLET SPREAD MOTION AFTER IMPINGEMENT ON THE WALL USING IMPROVED CIP METHOD (수정된 CIP방법을 이용한 벽면 충돌 후 액적의 퍼짐 현상에 대한 수치해석 연구)

  • Son, S.Y.;Ko, G.H.;Lee, S.H.;Ryou, H.S.
    • Journal of computational fluids engineering
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    • v.15 no.4
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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.