• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.14-19
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• 2004

The objective of the present work is to examine evaporation cooling of droplet due to surface roughness under radiative heat input condition. The surface temperatures varied from $80\~160^{\circ}C$ on aluminum alloy (AL 2024) and surface roughness was $0.18{\mu}m,\;1.36{\mu}m$. The results are as follows; Regardless of surface roughness under radiative heat input condition, as droplet diameter is larger, the in-depth temperature of solid decreases and evaporation time increases. In the case of $0.18{\mu}m\;and\;1.36{\mu}m$ of surface roughness, the larger the surface roughness is, the less the evaporation time is and the larger the temperature within the solid is. In the case of $Ra=0.18{\mu}m$ evaporation time and time averaged heat flux for radiative heat input case is shorter than for the conductive case.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.1-6
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• 1999

An experimental study was carried out to investigate the global spray behavior and spray characteristics of high-pressure fuel injector in the direct-injection goasoline enginet. The atomization characteristics of fuel spary such as mean droplet size, mean velocity , and velocity distribution were measured by the phase Doppler particle analyzer. The spray tip penetration and spray width were investigated by the result fo visualizaiton experiment. The quantitiative spary characteristics of injector spray were measured under various sparay conditions and ambient pressures. The results of experiment show that the increase in ambient pressure have influence on the spray tip penetration and spray development process. Also, the influence of injection pressure and measuring location on the mean velocity and droplet size distribution were discussed.

• Journal of ILASS-Korea
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• v.7 no.2
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• pp.22-30
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• 2002

A number of droplet breakup models have been developed to predict the diesel spray. The capabilities of droplet deformation and breakup models such as TAB, ETAB, DDB and APTAB models are evaluated in modeling the non-evaporating diesel sprays injected into atmosphere. New methods are also suggested that take into account the non- spherical shape of droplets and the reduced drag force by the presence of neighbouring droplets. The KIVA calculations with standard ETAB, DDB, and APTAB models predict well the spray tip penetrations of the experiment, but overestimate the Sauter mean Diameter(SMD) of droplets. The calculation with non spherical droplets injected from the nozzle shows very similar results to the calculation with spherical droplets. The drag coefficient which is linearly increased with the time after start of injection during the breakup time gives the smaller SMD that agrees well with the experimental result.

• 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.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.57-65
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• 2016

By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.47-52
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• 2008

The present study has focused on the characteristics of droplet formation from an inkjet nozzle driven by a piezoelectric actuator. As an operating fluid, ethylene glycol was used and the physical properties of it such as viscosity, surface tension, contact angle and shear stress were measured. During the experiments, various temperatures and driving voltages are imposed on a capillary tube. These conditions result in a proper drive condition or an overdrive condition. In case of the proper drive condition, an image processing technique is applied to measure the diameter of a single free drop. As a result, the size of droplet is increased when the driving voltage is increased from 160 V to 190 V at 25$^{\circ}C$ In the overdrive condition where temperature or driving voltage becomes higher than the proper drive condition, satellites and the misdirected jets happen.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.8-19
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• 2001

A number of atomization and droplet breakup models have been developed and used to predict the diesel spray characteristic. Most of these models could not provide reasonable computational result of the diesel spray characteristic because they have only considered the primary breakup. A hybrid model is, therefore, required to develop by considering the primary and secondary breakup of liquid jet. according to this approach, wave breakup(WB) model was used compute the primary breakup of the liquid jet and droplet deformation and breakup(DDB) model was used for the secondary breakup of droplet. Development of hybrid model by using KIVA-II code was performed by comparing with the experimental data of spray tip penetration and SMD from the literature. A hybrid model developed in this study could provide the good agreement with the experimental data of spray tip penetration. The prediction results of SMD were in good agreement between 0.5 and 1.0 ms after the start of injection. Numerical results obtained by the present hybrid model have the good agreement with the experimental data with the breakup time constant in WB model of 30, and DDB model constant Ck of 1.0 when the droplet becomes less than 95% of maximum droplet diameter injected.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.566-574
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• 1988

A study is described for obtaining real time in situ size and velocity measurements of the spray-droplet using crossed-beam interferometry. The optical arrangement is similar to dual-beam laser Doppler velocimetry(LDV). Droplets passing trough the probe volume scatter light to the collecting lens placed at 90.deg. off-axis angle. The dual-beam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to droplet diameter. The droplet size measurement is based upon the signal visibility. As the system is based on the Doppler effect, a single component of velocity is velocity is extracted concurrent with the size information. The validity of the method is evaluated by comparing its performance to widely accepted but limited technique, the collection method. By using 90.deg. off-axis scatter detection angle, the measurement of the droplet size and velocity distributions, and the local correlations between droplet sizes and velocities in relatively dense spray environments are made possible.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.801-806
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• 2000

This experimental study is to investigate the intermittent spray characteristics of a multi-hole nozzle in a heavy-duty DI diesel engine. Multi 8 hole$(d_n=0.25mm)$, Multi 3 hole$(d_n=0.42)$ and Sing hole nozzle$(d_n=0.25mm)$ were used in this experiment. By using the 2-D PDPA(phase Doppler particle analyzer), the droplet diameter and the velocity of a diesel spray injected intermittently from the multi and the single-hole nozzle into a still ambient were measured. In order to calculate the mean values such as mean velocity, SMD, AMD etc. and to analyze the intermittent characteristics, the time-window of 0.15ms were applied. In the spray, the small droplet$(D<10{\mu}m)$ was regarded as an air flow, and the correlation between the fuel droplet$(10{\mu}m and the air (low was examined. The normalized axial droplet-air relative velocity of the 8 hole, the 3 hole and the single hole nozzle was evaluated as 0.081, 0.067, 0.06 and in case of the radial droplet-air relative velocity, the normalized. value is 0.014, 0.013 and 0.008 respectively.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.21-26
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• 2012

Hydrophobic characteristics of high temperature metal surface were investigated by high-speed visualization of water droplet impact. An aluminum plate was used as the sample plate and the initial diameter of a water droplet was 2 mm. Transient behavior of a single droplet impinging on the surface with and without heating was captured by using a high speed camera running at 4,000 frames per second. The Leidenfrost phenomenon was demonstrated for the case of $300^{\circ}C$ surface temperature, however there was no rebounding of droplet on the cold plate due to hydrophilic nature. The experimental results show that the shape evolution of a droplet impinging on the surface varies with the Weber number, i.e. the ratio of impact inertia to capillary force. The overall water-repellent characteristics of the heated surface was very similar to that of the super hydrophobic surfaces.