• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.278-282
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• 2007

In the complex insulation system that is used in extra high voltage(EHV) devices, according to the trend for electric power equipment of high capacity and reduction of its size, macro interfaces between two different bulk materials which affect the stability of insulation system exist inevitably. In this paper, the dielectric strength decrease of the macro interfaces between epoxy and ethylene propylene diene terpolymer(EPDM) was estimated by using the applied voltage to breakdown time characteristics. Firstly, the AC short time dielectric strength of specimens was measured at room temperature. Then, the breakdown time was measured under the applied constant voltage which is 70% of short time breakdown voltage. With these processes, the life exponent n was determined by inverse power law, and the long time breakdown voltage can be evaluated. The best condition of the interface was LOS(low viscosity(350 cSt) silicone oil spread specimen). When 30 years last on the specimens, the breakdown voltage was estimated 44% of the short time breakdown voltage.

• Journal of Adhesion and Interface
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• v.15 no.1
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• pp.9-13
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• 2014

The purpose of this work is to investigate the specific gravity, thermal, and mechanical property changes of polypropylene (PP)/mica composites before and after solid-state extrusion. On increasing the filler content, the specific gravity of the composites increased. The specific gravity of the oriented specimen containing filler in PP matrix is found to be much smaller than that of pre-specimen due to the formation of more microvoids. The presence of microvoids in the case of oriented composite specimen significantly affected the tensile and flexural properties of the composites. Both flexural strength and modulus of the composites showed maxima when the mica contents was 10 wt%, regardless of the orientation via solid state extrusion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.792-801
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• 2000

The problem of phase change from liquid to solid in the inviscid plane-stagnation flow is theoretically investigated. The solution at the initial stage of freezing is obtained by expanding it in powers of time, and the final equilibrium state is determined from the steady-state governing equations. The transient solution is dependent on the three dimensionless parameters, but the equilibrium state is determined by one parameter of (temperature ratio/conductivity ratio). The effect of the fluid flow on the growth rate of the solid in the pure conduction problem can be clearly seen from the solution of the initial stage and the final equilibrium state. The characteristics of the transient heat transfer at the surface of the solid and the liquid side of the solid-liquid interface for all the dimensionless parameters are elucidated.

• Tribology and Lubricants
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• v.35 no.2
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• pp.94-98
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• 2019

The riblet structure like shark skin has been widely studied owing to its drag reduction and anti-fouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie-Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.51-57
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• 2005

Vertices terminating at free surface have been investigated extensively. Most of investigations, however, are focused on surface parallel vortices and little has been known about surface normal vortex or columnar vortex. Visualized experimental results utilizing LIF technique are discussed fur the purpose of characterization of columnar vortex interacting with a clean and a contaminated free surfaces and a solid body interface in the present investigation. The results reveal that surface tension changes due to surface contamination although bulk viscosity remains constant and eventually the behavior of a columnar vortex interacting with a contaminated free surface and a solid body interface are totally different from the clean free surface case.

• Ceramist
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• v.21 no.4
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• pp.349-365
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• 2018

Since the electrification of vehicles has been extended, solid-state batteries have been attracting a lot of interest because of their superior safety. Especially, polymer, sulfide, and oxide based materials are being studied as solid electrolytes, and each type of materials has advantaged and disadvantages over others. Oxide electrolytes has higher chemical and electrochemical stability compared to the other types of electrolytes. However, ionic conductivity isn't high enough as much as that of organic liquid electrolytes. Also, there are many difficulties of fabricating solid-state batteries with oxide based electrolytes because they require a sintering process at very high temperature (above ${\sim}800^{\circ}C$). Herein, we review recent studies of solid-state batteries with oxide based electrolytes about the ionic conductivity, interfacial reactions with Li metal, and preparation of solid-state cell.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.2
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• pp.90-94
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• 1998

This study aims at analyzing to treeing in the solid-solid interface which is insulation type of cable junction parts, the proceeding of tree-growth and electrical breakdown were research in the study. Interface was made artificially to detect how it influenced the insulating ability of the whole system, the specimen were XLPE generally used in cable. The interface conditions were divided into two parts. First condition being the one focused on the surface of interface, it was treated with sand paper (#80, #600, #1200). For the second condition, the pressure of interface was varied as the value of 1, 5, 10 [$kg/cm^2$]. Using above conditions, treeing and breakdown properties on tree-growth were respectively compared in details. As a result, breakdown time was shorter for the full range of supplied voltage in the case of interface existed in the joint than non-existed interface. In the case of existed interface, the interface which had high-interface pressure and painted with silicon insulating oil was the best in the aspect of breakdown characteristics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2404-2412
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• 1994

A mathematical model has been developed for predicting kinematic, thermal, and solidification histories of atomized droplets during flight. Liquid droplet convective cooling, recalescence, equilibrium-state solidification, and solid-phase cooling were taken into account in the analysis of the solidification process. The spherical shell model was adopted where the heterogeneous nucleation is initiated from the whole surface of a droplet. The growth rate of the solid-liquid interface was determined from the theory of crystal growth kinetics with undercooling caused by the rapid solidification. The solid fraction after recalescence was obtained by using the integral method. The thermal responses of atomized droplets to gas velocity, particle size variation, and degree of undercooling were investigated through the parametric studies. It is possible to evaluate the solid fraction of the droplet according to flight distance and time in terms of a dimensionless parameter derived from the overall energy balance of the system. It is also found that the solid fraction at the end of recalescence is not dependent on the droplet size and nozzle exit velocity but on the degree of subcooling.

• Journal of Surface Science and Engineering
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• v.57 no.2
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• pp.115-124
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• 2024

In advancing Li-ion battery (LIB) technology, the solid electrolyte interface (SEI) layer is critical for enhancing battery longevity and performance. Formed during the charging process, the SEI layer is essential for controlling ion transport and maintaining electrode stability. This research provides a detailed analysis of how vinylene carbonate (VC) influences SEI layer formation. The integration of VC into the electrolyte markedly improved SEI properties. Moreover, correlation analysis revealed a connection between electrolyte decomposition and battery degradation, linked to the EMC esterification and dicarboxylate formation processes. VC facilitated the formation of a more uniform and chemically stable SEI layer enriched with poly(VC), thereby enhancing mechanical resilience and electrochemical stability. These findings deepen our understanding of the role of electrolyte additives in SEI formation, offering a promising strategy to improve the efficiency and lifespan of LIBs.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.355-362
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• 2009

Most material of engineering interest undergoes solidification process from liquid to solid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material which governs the physical properties of final product. In this paper, we expand our previous two-dimensional numerical technique to three-dimensional simulation for computing dendritic solidification process with fluid convection. We used Level Contour Reconstruction Method to track the moving liquid-solid interface and Sharp Interface Technique to correctly implement phase changing boundary condition. Three-dimensional results showed clear difference compared to two-dimensional simulation on tip growth rate and velocity.