• Transactions on Electrical and Electronic Materials
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• v.12 no.3
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• pp.110-114
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• 2011

Polymeric films of high chemical stability and mechanical strength covered with a thin metallic film have been extensively used in various fields as electric and electronic materials. In this study, we have chosen polypropylene (PP) as the polymer due to its outstanding chemical resistance and good creep resistance. We coated thin nickel film on PP films by the electroless plating process. The surfaces of PP films were pre-treated and modified to increase the adhesion strength of metal layer on PP films, prior to the plating process, by an environment-friendly process with atmospheric plasma generated using dielectric barrier discharges in air. The surface morphologies of the PP films were observed before and after the surface modification process using a scanning electron microscope (SEM). The static contact angles were measured with deionized water droplets. The cross-sectional images of the PP films coated with thin metal film were taken with SEM to see the combined state between metallic and PP films. The adhesion strength of the metallic thin films on the PP films was confirmed by the thermal shock test and the cross-cutting and peel test. In conclusion, we made a composite material of metallic and polymeric films of high adhesion strength.

• Wind and Structures
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• v.24 no.1
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• pp.79-93
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• 2017

Wind-induced fluctuating internal pressures in a building with a dominant opening can be described by a second-order non-linear differential equation. However, the accuracy and efficiency of the governing equation in predicting internal pressure fluctuations depend upon two ill-defined parameters: inertial coefficient $C_I$ and loss coefficient $C_L$, since $C_I$ determines the un-damped oscillation frequency of an air slug at the opening, while $C_L$ controls the decay ratio of the fluctuating internal pressure. This study particularly focused on the value of loss coefficient and its influence factors including: opening configuration and location, internal volumes, as well as wind speed and approaching flow turbulence. A simplified formula was presented to predict loss coefficient, therefore an approximate relationship between the standard deviation of internal and external pressures can be estimated using Vickery's approach. The study shows that the loss coefficient governs the peak response of the internal pressure spectrum which, in turn, will directly influence the standard deviation of the fluctuating internal pressure. The approaching flow characteristic and opening location have a remarkable effect on the parameter $C_L$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.1047-1054
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• 2002

To improve the fuel consumption and exhaust emission for gasoline engines, GDI(Gasoline Direct Injection) system was spotlighted to solve above requirements. Thus, many researchers have been studied to investigate the spray characteristics and the mixture formation of GDI injector. In this study, we tried to study the spray characteristics of a gasoline direct injector by using entropy analysis and PlV methods. The entropy analysis is based on the concept of statistical entropy, and it identifies the degree of homogeneity in the fuel concentration. The PlV method was adopted to determine the fluid dynamics information at the spray. From the applied results on a direct injection gasoline spray, we could find that the direct diffusion phenomena was a dominant factor in the formation of a homogeneous mixture at downstream of GDI spray especially under vaporizing ambient conditions, and mixing phenomena was also progressed by momentum exchange with induced air. In addition, the correlation between entropy and vorticity strength enabled to find their relation.

• Journal of Korean Society for Atmospheric Environment
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• v.31 no.6
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• pp.530-537
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• 2015

The wet electrostatic precipitator (wet ESP) is an effective control device which removes submicron particles reentrained in a collection plate and water soluble gas. However, its collection efficiency decreases, as its operation is subject to water-induced distortion of the collection electrode. In order to make up for the limitation, we modified the wet ESP system by installing electrosprayed discharge electrodes. The modified wet ESP system can wash both the collection plate and discharge electrode. As a result, we were able to fabricate a compact wet ESP with a small specific collecting area ($0.18m^2(m^3/min)$) that can accomplish a high collection efficiency of fine particles (97.1%). In addition, the device obtained a relatively low specific corona power of approximately $10W/(m^3/min)$.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.795-800
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• 2000

A CCFL(Counter Current Flow Limit) test have been performed in narrow annular gaps with large diameter, because it has been confirmed that the CCFL phenomena affected the critical power in hemispherical narrow gap geometries from the SONATA(Simulation Of Naturally Arrested Thermal Attack)-IV (In-Vessel)/VISU(Visualization)-II experiments. The objectives of the CCFL experiments are to investigate the small gap sizes(1, 2mm) effect on CCFL under the large diameter condition and to confirm the findings of the VISU-II study that global dryout in hemispherical narrow gaps was induced by the CCFL. The test section was made of acrylic resin to allow visual observation on the two-phase flow behaviors inside annular gaps. It was observed from visualization that a part of water supplied was accumulated in the upper plenum and a significant increase in the differential pressure across the gap was occurred, which was the definition of the CCFL occurrence in this experimental study. From the experimental results in annular gap with large diameter it can be known that an increase in the differential pressure was not big at small air flow-rates. When the CCFL was occurred, the differential pressure across gaps was increased significantly and a water accumulated in the upper plenum. The occurrence of CCFL was correlated using the Wallis parameter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1335-1341
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• 2003

This paper describes the process of nanoparticle synthesis by laser ablation of microparticles and consolidated sample. We have generated nanoparticles by high-power pulsed laser ablation of AI, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355nm, FWHM 6ns, fluence $0.8{\sim}2.0J/cm^2$). Microparticles of mean diameter $18{\sim}80{\mu}m$ are ablated in the ambient air. The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence, collector position and compacting pressure on the distribution of particle size is investigated. To better understand the process of laser ablation of microparticle(LAM), we investigated the Nd: YAG laser-induced breakdown of Cu microparticle using time-resolved optical shadow images. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

• Membrane Journal
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• v.24 no.3
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• pp.240-248
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• 2014

Porous PVDF hollow fiber membranes were prepared by hybrid process of TIPS(thermally induced phase separation) and stretching for membrane distillation. The tests were conducted to investigate that permeability of the membrane could be enhanced by reducing membrane wall thickness. During fiber spinning, dope discharge rate from nozzle was reduced and flow rate of bore fluid increased to make the wall thickness thinner. As dope discharge rate from nozzle was reduced and flow rate of bore fluid increased, the membrane wall thickness was reduced. As a result, air permeability, water permeability and vapor permeability of the membranes increased.

• Journal of the Korean Institute of Landscape Architecture
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• v.27 no.4
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• pp.50-58
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• 1999

This study was carried out to investigate the growth characteristics and propagation methods of L. obtusiloba as a woody landscape plant. The results are obtained as follows: L. obtusiloba was dioecious shrub and shaped with bush type. Leaves were ovate, obtuse, cordate, 7.05 cm long, 7.20 cm wide, and petiole 2.0 cm long. Flowers of L. obtusiloba were diclinous. Soil acidity ranged from pH 4.06 to 5.53 with the lowest at the Mt. Soo-Ri. Mt. Soo-Ri located near factory district, which was considered to damaged by environmental deteoration. While soil organic matter was highest at Mt. Soo-Ri, inorganic nutrients were low. L. obtusiloba grows in the area with low soil acidity and low content of inorganic. Therefore it seemed to be tolerant to air pollution. L. Obtusiloba was high seed germination rate in the plug box and its shoots were longer than seeding box and softwood cutting of L. obtusiloba showed the rooting rate of 50% at 5,000ppm on June 23. To develop a mass propagation method of Korean native L. obtusiloba through an axillary bud culture as a woody landscape plant, about 2∼3 cm shoots induced from explant were subcultured to new media contained different growth regulators. Shoots multiplied most effectively on a WPM containing 1.0 mg/l BA, producing 5.5 shoots with a shoot length of 2.5 cm per shoot explant.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.91-98
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• 2000

We investigated a uniform temperature zone, produced by double flame structure of a co flow CH4/air partially premixed flame, to be used as a temperature calibration source for laser diagnostics. A broadband N2 CARS(coherent anti-Stokes Raman spectroscopy) system with a modeless laser was used for temperature measurement. When the stoichiometric ratio was 1.5, we found the uniform temperature zone in radial direction of the flame of which the averaged temperature was 2110 K with standard deviation 24 K. In the stoichiometric ratio range between 2.0 and 2.5, we found very stable temperature-varying zones in vertical direction at the center of the flame. The size of the zone was approximately 15 mm and it covered a temperature range from 300 K to 1900 K. We also suggest that this zone can be used as a calibration source for 2-D PLIF(planar laser induced flurescence) temperature measurement.

• Tribology and Lubricants
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• v.24 no.6
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• pp.362-367
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• 2008

Tubes in nuclear steam generators are held up by supports because the tubes are long and slender. Fluid flows of high-pressure and high-temperature in the tubes cause oscillating motions between tubes and supports. This is called as FIV (flow induced vibration), which causes fretting wear in contact parts of tube-support. The fretting wear of tube-support can threaten the safety of nuclear power plant. The tube and support materials were Inconel 690 and STS 409. The wear tests were conducted in various environments, which are in water without flow, in flowing water and in flowing water with air. The results showed that the flow of water influenced on the wear-life of tube. The wear-life of tube decreased in water flow as compared with wear-life in stationary water.