• 한국전산유체공학회지
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• 제13권3호
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• pp.8-13
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• 2008

We present a numerical simulation technique and some preliminary results of the impact and spreading of a droplet containing particles on the solid substrate in 2D. We used the 2nd-order Adams-Bashforth / Crank-Nicholson method to solve the Navier-Stokes equation and employed the level-set method with the continuous surface stress for description of droplet spreading with interfacial tension. The impact velocity has been generated by the instantaneous gravity. The distributed Lagrangian-multipliers method has been combined for the implicit treatment of rigid particles and the discontinuous Galerkin method has been used for the stabilization of the interface advection equation. We investigated the droplet spreading by the inertial force and discussed effects of the presence of particles on the spreading behavior using an example problem. We observed reduced oscillation and spread for the particulate droplet.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.114-121
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• 2003

Water droplet erosion is one of major concerns in the design of modern large fossil steam turbines because it causes serious operational problems such as performance degradation and reduction of service life. A new erosion model has been developed in the present study for the prediction of water droplet erosion of rotor blades operated in wet steam conditions. The major four erosion parameter : impact velocity, impacting droplet flow rate, droplet size and hardness of target are involved in the model so that it can also be used for engineering purpose at the design stage of rotor blades. Comparison of the predicted erosion rate with the measured data obtained from the practical steam turbine operated for more than 90,000 hours shows good agreement.

• 한국가시화정보학회지
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• 제2권1호
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• pp.25-31
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• 2004

Droplet size is one of the most important parameter which controls the performance of the combustion system using liquid fuel or oxidizer. Droplet formation and its size are mainly affected by the injection velocity and ambient gas density. Recently, droplet size measurement was conducted by PDPA or Malvern particle analyzer using laser light. But at this paper image processing method was developed to measure droplet size. And its validation was investigated with reticle.

• 한국분무공학회지
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• 제12권4호
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• pp.198-203
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• 2007

In the present work, surface wetting effect on spread-splash regime and transition criterion of the water and ethanol droplets impacting an unheated dry wall has been experimentally investigated. The droplet was directed on a polished STS plate and a glass slide, and the impinging behavior was visualized and recorded using a CCD camera. Droplet diameter and velocity approaching the wall were measured as well. The critical Sommerfeld number representing the spread-splash boundary for the ethanol droplet impinging on the substrates turned out to be smaller compared to that for the water droplet impinging on the substrates with the surface roughness condition remained unchanged. The shift of the transition boundary is considered to be due to the effect of the surface wettability represented by static contact angle and surface tension of droplet.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1897-1902
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• 2004

Numerical analysis of the heat transfer associated with droplet impact on a hot solid surface is performed by solving the mass, momentum and energy equations for the liquid-gas region. The deformed droplet shape is tracked by a level set method which is modified to achieve volume conservation during the whole calculation procedure and to include the effect of contact angle at the wall. The numerical method is validated through test calculations for the cases reported in the literature. Based on the numerical results, the effects of advancing/receding contact angle, impact velocity and droplet size on the heat transfer during droplet impact are quantified.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.87-93
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• 2001

In this study, the velocity characteristics of liquid elements formed by two impinging jets is analysed using double pulse image capturing technique. For the droplets formed by low speed impinging jets, the droplet velocities are higher with smaller azimuthal and impingement angle. The maximum droplet velocities are about 25 % lower than jet velocity. With an increase of azimuthal angle, the shedding angles increases but remains lower than azimuthal angle. The velocities of ligaments formed by high speed impinging jets gradually decreases with an increase of azimuthal angle. The maximum ligament velocities are about 40 % lower than jet velocity. Higher impingement angles produce lower ligament velocities. The shedding angles of ligament almost increases with the same value of azimuthal angle, which implies that the moving direction of ligaments is radial from the origin as the impingement point.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.263-268
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• 2004

The characteristics of Diesel spray droplets, such as the velocity and the diameter were simultaneously measured by using an improved Interferometric Laser Imaging for Droplet Sizing method. The experiments were carried out using an accumulator-type unit injector system and a constant-volume vessel. Two dimensional cross-section photographs of sprays were also taken using a double-pulsed Nd- YAG laser sheet and a linear array CCD camera. As a result, interesting relations between the droplets diameter and the velocity were found.

• 한국분무공학회지
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• 제6권2호
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• pp.1-8
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• 2001

In this study, the velocity characteristics of liquid elements formed by two impinging jets is analysed using double pulse image capturing technique. For the droplets formed by low speed impinging jets, the droplet velocities are higher with smaller azimuthal and impingement angle. The maximum droplet velocities are about 25 % lower than jet velocity. With an increase of azimuthal angle, the shedding angles increases but remains lower than azimuthal angle. The velocities of ligaments formed by high speed impinging jets gradually decreases with an increase of azimuthal angle. The maximum ligament velocities are about 40% lower than jet velocity. Higher impingement angles produce lower ligament velocities. The shedding angles of ligament almost increases with the same value of azimuthal angle, which implies that the moving direction of ligaments is radial from the origin as the impingement point.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.147-152
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• 2002

When a liquid is supplied through a nozzle onto a relatively non-wetting inclined solid surface, a narrow rivulet forms. There exist several regimes of rivulet flow depending on various flow conditions. In this paper, the fundamental mechanism behind the transition of a linear rivulet to a droplet flow is investigated. The experiments show that the droplet flow emerges due to the necking of a liquid thread near the nozzle. Based on the observation, it is argued that when the retraction velocity of a liquid thread exceeds its axial velocity, the bifurcation of the liquid thread occurs, and this argument is experimentally verified.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1279-1287
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• 2004

The vaporization characteristics of a liquid heptane droplet in a supercritical nitrogen flow are numerically studied. The transient conservation equations of mass, momentum, energy, and species are expressed in an axisymmetric coordinate system. The governing equations are solved time marching method with preconditioning scheme. The modified Soave-Redlich-Kwong equation of state is employed for taking account of real gas effects such as thermodynamic non-ideality and transport anomaly. Changing the convective velocity and ambient pressure, several parametric studies are conducted. The numerical results show that the two parameters, Reynolds number and dimensionless combined parameter(${\mu}$s/${\mu}$d)(equation omitted), have influence on supercritical droplet vaporization.