• Carbon letters
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• 제15권2호
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• pp.117-124
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• 2014

Conductive polymer composites (CPCs) consist of a polymeric matrix and a conductive filler, for example, carbon black, carbon fibers, graphite or carbon nanotubes (CNTs). The critical amount of the electrically conductive filler necessary to build up a continuous conductive network, and accordingly, to make the material conductive; is referred to as the percolation threshold. From technical and economical viewpoints, it is desirable to decrease the conductive-filler percolation-threshold as much as possible. In this study, we investigated the effect of polymer/conductive-filler interactions, as well as the processing and morphological development of low-percolation-threshold (${\Phi}c$) conductive-polymer composites. The aim of the study was to produce conductive composites containing less multi-walled CNTs (MWCNTs) than required for pure polypropylene (PP) through two approaches: one using various mixing methods and the other using immiscible polymer blends. Variants of the conductive PP composite filled with MWCNT was prepared by dry mixing, melt mixing, mechanofusion, and compression molding. The percolation threshold (${\Phi}c$) of the MWCNT-PP composites was most successfully lowered using the mechanofusion process than with any other mixing method (2-5 wt%). The mechanofusion process was found to enhance formation of a percolation network structure, and to ensure a more uniform state of dispersion in the CPCs. The immiscible-polymer blends were prepared by melt mixing (internal mixer) poly(vinylidene fluoride) (PVDF, PP/PVDF, volume ratio 1:1) filled with MWCNT.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.93-102
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• 2021

The analysis of the fluid flow characteristics in reactor pressure vessel is an important part of the hydraulic design of nuclear power plant, which is related to the structure design of reactor internals, the flow distribution at core inlet and the safety of nuclear power plant. The flow distribution and mixing characteristics in the pressurized reactor vessel for the 1000MWe advanced pressurized water reactor is analyzed by using Computational Fluid Dynamics (CFD) method in this study. The geometry model of the full-scaled reactor vessel is built, which includes the cold and hot legs, downcomer, lower plenum, core, upper plenum, top plenum, and is verified with some parameters in DCD. Under normal condition, it is found that the flow skirt, core plate holes and outlet pipe cause pressure loss. The maximum and minimum flow coefficient is 1.028 and 0.961 respectively, and the standard deviation is 0.019. Compared with other reactor type, it shows relatively uniform of the flow distribution at the core inlet. The coolant mixing coefficient is investigated with adding additional variables, showing that mass transfer of coolant occurs near the interface. The coolant mainly distributes in the 90° area of the corresponding core inlet, and mixes at the interface with the coolant from the adjacent cold leg. 0.1% of corresponding coolant is still distributed at the inlet of the outer-ring components, indicating wide range of mixing coefficient distribution.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.283-288
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• 1996

Direct safety injection into the reactor vessel downcomer annulus(DVI) is a fundamental feature of the KNGR(Korean Next Generation Reactor) four-train safety injection system. The numerical analysis of thermal mixing of ECC(Emergency Core Cooling) water through DVI with the water in the RVDC(Reactor Vessel Downcomer) annulus has been performed, in order to study the impact of nozzle location on the pressurized thermal shock and safety analysis. The results of this study show that the thermal mixing due to the natural circulation induced by the limiting accident conditions is sufficient to prevent temperature in the RVDC from dropping to the level of concern for PTS. When the DVI nozzle is located right above the cold leg, the temperature distribution at the outlet of flow field is most uniform. The tool used for numerical analysis is CFDS-FLOW3D.

• 상하수도학회지
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• 제7권1호
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• pp.29-36
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• 1993

The complex nature of low flow mixing in natural channels has been investigated using both laboratory experiments and the numerical solution of a proposed mathematical model that is based on a set of mass balance equations describing the mixing and mass exchange mechanisms. Laboratory experiments, which involved collection of channel geometry, hydraulic, and dye dispersion test data, were conducted in a model of four pool and riffle sequences in a 49-m long tilting flume. The experimental results show that flow over the model pool-riffle sequences is highly non-uniform. Concentration-time curves are significantly skewed with long tails. Comparison between measured and predicted concentration-time curves shows good agreement in the general shape, peak concentration and time to peak. The proposed model shows significant improvement over the conventional one-dimensional dispersion model in predicting natural mixing processes in open channels under low flow conditions through pools and riffles.

• 한국표면공학회지
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• 제50권5호
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• pp.373-379
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• 2017

Dry processes like evaporation and sputtering in vacuum chamber are difficult to make a uniform, large area and high quality film on thin PET substrate because of PET degradation and bad adhesion. On the other hand, wet processes like electro or electroless plating have complex processes and require high environmental cost. In this study, we successfully prepared $2{\mu}m$ Zn/Cu/Ni multilayers coated on $12{\mu}m$ polyethylene terephthalate (PET) substrate by using dry-wet mixing processes. Their surface electric resistances were evaluated around $0.2{\Omega}$ by using 4 probe measurements. Furthermore, their corrosion resistance also evaluated by natural potential test and compared with other wet, dry and mixing process samples.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.48-54
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• 2006

A visualization study of flow characteristics in a mixer using multi-nozzle bubbling was performed. The mixer is filled with liquid glycerin (dynamic viscosity = $1000mPa{\cdot}$ s at $25^{\circ}C$) and convective mixing is induced by air bubbles generated from 9 orifices installed on the bottom of the mixer. To visualize the flow field, PIV (Particle Image Velocimetry) system consisting of 532nm Nd:YAG laser, $2k\times2k$ CCD camera and synchronizer is adopted. The bubbles generated with uniform size and frequency form bubble stream, and bubble streams rise vertically without interaction between bubble streams. Mixing efficiency is affected by the height of bubbler and the effective height of bubbler is 20mm from the bottom of the mixer.

• 한국수소및신에너지학회논문집
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• 제28권6호
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• pp.663-668
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• 2017

SOFC anode fabricated core-shell using machano-fusion method using core with submicron size Ni, nano size YSZ for shell. Using prepared core-shell, depending on the thickness of the shell, we studied how the characteristics of sintering and SOFC cell change by sintering the anode. The Ni-YSZ core-shell has a Ni core of 0.5 to $1.2{\mu}m$ over 2 to 7 YSZ of 15 to 20 nm is, and as the high speed mixing time increases, the YSZ number increases and the shell thickness becomes uniform increased. When the fuel electrode is manufactured with core-shell, it has superior sintering property, has grain of uniform size compared with the one synthesized by general mixing, the falling path is short, the conductors (electrons and ions) connection is excellent, the electrical conductivity has become excellent. The thicker the shell, the lower the electrical conductivity. When the thickness of shell ranged from 46 to 139 nm and 61 to 81 nm, the performance was the highest and the ASR was the smallest.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2009년도 추계학술발표회 논문집
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• pp.79-84
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• 2009

Understanding the polymer adsorption in particle/binder/solvent system is important to achieve successful film products. While most of the reported work has dealt with the suspension microstructure, a few studies have focused on film formation. We investigated the effect of adsorption on film formation through measurement of adsorption amount in suspension and stress development in drying film with respect to mixing time ($t_m$). All of the adsorption amount (PVA), characteristic stress ($\sigma_{ch}$) exhibited similarities expressed by the form of $1-e^{t_m/{\tau}}$. The porous and non-unifonn dried film at short tm became close-packed and uniform with longer $t_m$. We found that polymer adsorption plays the key role in film fonnation as it introduces steric repulsion in suspension and suppresses the flocculation during solvent evaporation. We also found that the mixing time for the saturated polymer adsorption is the important variable to acquire the consolidated and uniform film microstructure.

• 한국수소및신에너지학회논문집
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• 제23권6호
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• pp.678-687
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• 2012

Concentration fields of solid powder in a liquid fuel were quantitatively measured by a visualization technique. The measurement system consists of a camcoder and three LCD monitors. The solid powder (glass powder) were filled in a head tank which was installed over a main mixing tank ($D{\times}H$, $310{\times}370mm$). The main mixing tank was filled with JetA1 fuel oil. With a sudden opening of the upper tank by pressurized nitrogen gas with 1.9 bar, the solid powder were poured into the JetA1 oil. An impeller type agitator was being rotated in the mixing with 700 rpm for the enhancements of mixing. Uniform visualization for the mixing flow field was made by the light from the three LCD monitors, and the visualized images were captured by the camcoder. The color images captured by the camcoder The color information of the captured images was decoded into three principle colors R, G, and B to get quantitattive relations between the concentrations of the solid powder and the colors. To get better fitting for the strong non-linearity between the concentration and the color, a neural network which has strong fitting performances was used. Analyses on the transient mixing of the solid powders were quantitatively made.

• 한국전산유체공학회지
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• 제15권1호
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• pp.56-63
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• 2010

Since emission regulations for vehicles have become more stringent, SCR technology has drawn a strong attention in order to reduce NOx emissions. Optimal design of a reductant injection nozzle and a multi-hole plate located between the cone and catalyst is critical in that the uniform distribution of reductant is necessary to maximize the NOx conversion efficiency and minimize the slip of reductant in SCR. In this work, an LPG fuel(C3H8 in vapor state) was used as a reductant for LPG vehicles. A Realizable k-$\varepsilon$ model is used for turbulence, and SCR body is defined as porous media with inertia and viscous resistances measured in this work. Effect of the number of nozzle holes on the flow mixing index was analyzed, which revealed that a four hole nozzle shows the best performance in terms of uniformity of flow. An installment of a multi-hole plate at the entrance of catalyst was evaluated with flow mixing index, uniformity of flow, and pressure drop. A multi-hole plate with gradual hole diameter change in three steps showed the best uniformity of flow within the conditions suggested in this work.