• 수산해양기술연구
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• 제43권3호
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• pp.192-205
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• 2007

The objective of this study was to investigate the optimal shapes and arrangements of sinkers attached to net cages to prevent their deformation in a current. A series of model experiments were conducted in a circulating water channel, using 5 different types of sinker(high-weighted ball, low-weighted ball, columntype, egg-shaped and iron bar-framed) and 2 types of square net cage constructed from both Nylon Raschel netting and Nylon knotted netting, on a 1/20th scale. The deflection of the model nets against the flow was smallest with the iron bar-framed weight compared to the other four types of sinker. It was expected that the optimal shapes of sinkers would be either the ball or egg-shape; however, iron bar-framed weight actually had larger drag forces. The dispersed deployment of sinkers on the bottom frames of model net cages performed better with relatively slow flows, while the concentrated deployment at 4 corners functioned better with relatively fast flows, in preventing the nets from becoming severely deformed. The deformation of the net cages was larger for the Nylon knotted netting than the Nylon Raschel netting. With respect to flow resistance, the Nylon Raschel netting, rather than the Nylon knotted netting, was more suitable for construction of net cages.

• KSBB Journal
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• 제5권1호
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• pp.59-67
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• 1990

생성물의 분리 및 효소의 회수를 위하여 수평흐름 한외여과장치를 부착한 기포탑에서 섬유소의 연속적인 효소 가수분해 반응을 연구하였다. 기포탑을 효소 가수분해 반응 공정에 이용할 경우 기체유속의 범위는 1-3cm / sec로 기포의 합체현상이 발생하지 않는 dispersed bubble flow 영역이 적합하며 혼합도 거의 완전하게 이루어짐을 확인하였다. 효소 회수장치에 한계분자량이 $10^4$인 여과막을 사용하였을 경우 효소의 활성이 저하되지 않은 채 대부분이 회수되었고 glucose 및 cellobiose의 배제율은 0이었다. 따라서 수평흐름 한외 여과장치는 효소의 연속회수장치로 작합하였으며 반응생성물이 연속적인 분리로 섬유소의 당화율을 증가시켰다. 화분식 반응의 경우 반응시간이 8시간이내에서 실험치는 성능식에 잘 부합되었으나 반연속식 및 연속식 반응의 경우에는 이론값과 차이가 있었다. 이는 반응기 내에서의 효소의 변성에 기인된다. 반연속식 및 연속식 반응의 경우 희석율을 증가시킴에 따라 전환율은 증가하나 반응액중의 환원당의 농도는 낮아진다. 따라서 적정한 기질 공급속도 및 희석율은 효소의 회수비용, 생성물의 농축비용 및 기질의 공급비용등의 경제적 요소를 고려하여 판단하여야 한다. 이상의 결과로부터 수평흐름 한외여과장치를 효소 회수장치로 기포탑에 응용할 경우, 효소의 재사용이 가능할 뿐 아니라 당화율을 증가시킴으로서 연속반응기로 효과적이라고 판단되었다.

• 한국가스학회지
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• 제20권4호
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• pp.65-77
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• 2016

Fischer-Tropsch 반응기 내 복잡한 반응과 흐름을 상세히 모델링하는 것은 CFD 분야에 있어 도전적 과제이다. Fischer-Tropsch 반응은 여러 가지 탄소수를 가진 탄화수소들을 만들어내는데, 탄화수소에는 무수히 많은 이성질체가 존재하는 이유로 모든 화학종에 대해서 각각의 반응속도식을 도출해 적용하는 것은 어렵다. 이의 극복을 위해 기존 연구들에서 사용된 반응속도식 모델링 방법론들을 분석한 뒤, 화학종별 상세한 반응속도식 적용을 위해 non-Anderson-Schulz-Flory 방법론을 선정하여 상세 모델링을 진행하였다. 또한 반응 특성상 다상 흐름 형태를 띠는데, 다상 흐름 모델링의 경우 상간의 간섭이나 분산상의 분포 및 유동 형태 등에 따라 적합한 모델링 방법론이 다르다. 그러나 기존 연구들에서는 타당성에 대한 논의나 근거 제시 없이 각양각색의 내부 흐름 모델링 방법론이 사용되고 있다. 실험을 통해 내부 흐름 형태를 관찰한 뒤 유동 형태에 따른 모델링을 진행하는 것이 최선이나, 자원 여건상 어려움이 있어, 본 연구에서는 전통적인 유체역학 이론에 근거해 내부 흐름 형태를 먼저 추론하고 Mixture 모델 방법론을 선정하여 체계적인 CFD 모델링을 진행함으로써, 사용된 방법론에 대한 근거를 마련하고자 하였다. 10가지 실험조건에서 진행한 실험 결과와 본 연구의 시뮬레이션 결과를 비교하였으며, 이를 통해 본 연구가 제안하는 체계적 모델링 방법론의 타당성을 입증하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.121-128
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• 2009

During a hypothetical high-pressure accident in a nuclear power plant (NPP), molten corium can be ejected through a breach of a reactor pressure vessel (RPV) and dispersed by a following jet of a high-pressure steam in the RPV. The dispersed corium is fragmented into smaller droplets in a reactor cavity of the NPP by the steam jet and released into other compartments of the NPP by a overpressure in the cavity. The fragments of the corium transfer thermal energy to the ambient air in the containment or interact chemically with steam and generate hydrogen which may be burnt in the containment. The thermal loads from the ejected molten corium on the containment which is called direct containment heating (DCH) can threaten the integrity of the containment. DCH in a NPP containment is related to many physical phenomena such as multi-phase hydrodynamics, thermodynamics and chemical process. In the evaluation of the DCH load, the melt dispersion rates depending on the RPV pressure are the most important parameter. Mostly, DCH was evaluated by using lumped-analysis codes with some correlations obtained from experiments for the dispersion rates. In this study, MC3D code was used to evaluate the dispersion rates in the APR1400 NPP during the high-pressure accidents. MC3D is a two-phase analysis code based on Eulerian four-fields for melt jet, melt droplets, gas and water. The dispersion rates of the corium melt depending on the RPV pressure were obtained from the MC3D analyses and the values specific to the APR1400 cavity geometry were compared to a currently available correlation.

• 한국재료학회지
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• 제17권1호
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• pp.11-17
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• 2007

Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/solid, liquid/gas, flow ana solidification speed simultaneously. In this study, mixing which is the key technology to this synthesis method was studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers investigated. Two inlets for different liquid metal meet ana merge like 'Y' shape tube having various shapes and radios of curve. The performance of mixer was evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection were presented to understand effect of mixer shape on mixing. The simulations show that the Reynolds number (Re) is the important factor to mixing and dispersion of $TiB_2$ particles. Mixer was designed according to the simulation, and $Cu-TiB_2$ nano composites were evaluated. $TiB_2$ nano particles were uniformly dispersed when Re was 1000, and cluster formation and reduction in volume fraction of $TiB_2$ were found at higher Re.

• 한국재료학회지
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• 제19권12호
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• pp.637-643
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• 2009

In this study, we analyzed the effect of silicon oxynitride matrix on the optical properties of Au nanoparticles dispersed on composite film and explored the effectiveness of the silicon in fine tuning the refractive index of the composite film for applications in optical waveguide devices. The atomic fraction of nitrogen in $SiO_xN_y$ films was controlled by varying the relative flow ratio of nitrogen gas in reactive sputtering and was evaluated optically using an effective medium theory with Bruggeman geometry consisting of a random mixture between $SiO_2$ and $Si_3N_4$. The Au nanoparticles were embedded in the $SiO_xN_y$ matrix by employing the alternating deposition technique and clearly showed an absorption peak due to the excitation of surface plasmon. With increasing nitrogen atomic fraction in the matrix, the surface plasmon resonance wavelength shifted to a longer wavelength (a red-shift) with an enhanced resonance absorption. These characteristics were interpreted using the Maxwell-Garnett effective medium theory. The formation of a guided mode in a slab waveguide consisting of 3 $\mu$m thick Au:$SiO_xN_y$ nanocomposite film was confirmed at the telecommunication wavelength of 1550 nm by prism coupler method and compared with the case of using $SiO_2$ matrix. The use of $SiO_xN_y$ matrix provides an effective way of controlling the mode confinement while maintaining or even enhancing the surface plasmon resonance properties.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.738-745
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• 2015

The catalytic exchange of hydrogen isotopes between hydrogen and water has been known to be a very useful process for the separation of tritium from tritiated water. For the process, a highly active hydrophobic catalyst is needed. This study provides an effective fabrication method of size-controlled platinum/poly[styrene-divinylbenzene-tri(propylene glycol) diacrylate] [Pt/poly(SDB-TPGDA)] hydrophobic catalyst beads with a narrow size distribution. Platinum nanoparticles were prepared by ${\gamma}$-ray-induced reduction in the aqueous phase first, and then uniformly dispersed in SDB-TPGDA comonomer after the hydrophobization of platinum nanoparticles with alkylamine stabilizers. The porous Pt/poly(SDB-TPGDA) hydrophobic catalyst beads were synthesized by the UV-initiated polymerization of the mixture droplets prepared in a capillary-based microfluidic system. The size of as-prepared catalyst beads can be controlled in the range of $200-1,000{\mu}m$ by adjusting the flow rate of dispersed and continuous phases, as well as the viscosity of the continuous phase. Sorbitan monooleate and cyclohexanol were used as coporogens to control the porosities of the catalyst beads.

• 한국염색가공학회지
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• 제33권4호
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• pp.280-287
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• 2021

Generating electricity by using water in many energy harvesting system is due to their simplicity, sustainability and eco-friendliness. Evaporation-driven moist-electric generators (EMEGs) are an emergent technology and show great potential for harvesting clean energy. In this study, we report a transpiration driven electro kinetic power generator (TEPG) that utilize capillary flow of water in an asymmetrically wetted cotton fabric coated with carbon black. When water droplets encounter this textile EMEG, the water flows spontaneously under capillary action without requiring an external power supply. First carbon black sonicated and dispersed well in three different solvent system such as dimethylformamide (DMF), sodiumdedecylbenzenesulfonate (SDBS-anionic surfactant) and cetyltrimethylammoniumbromide (CTAB-cationic surfactant). A knitted cotton/PET fabric was coated with carbon black by conventional pad method. Cotton/PET fabrics were immersed and stuttered well in these three different systems and then transferred to an autoclave at 120 ℃ for 15 minutes. Cotton/PET fabric treated with carbon black dispersed in DMF solvent generated maximum current up to 5 µA on a small piece of sample (2 µL/min of water can induce constant electric output for more than 286 hours). This study is high value for designing of electric generator to harvest clean energy constantly.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
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• pp.143-150
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• 2000

Wet-chemical process using ammonia to precipitate aluminum ion dissolved in a zirconia sol solution is examined. Formation of crystalline bayerite is unfavorable for fine dispersion of zirconia nanoparticles in alumina matrix after heat treatment. To avoid the bayerite formation, it was preferred to make a precipitation with a diluted ammonia or with an ammonia gas flow at high temperature. By optimizing the precipitation process and the calcination temperature, we successfully prepared the uniform microstructure in which tetragonal zirconia particles of ∼30nm is finely dispersed within the alumina grains.

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1331-1335
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• 2010

A novel spherical carbon composite material, in which nanosized disordered carbons are dispersed in a soft carbon matrix, has been prepared and investigated for use as a potential anode material for lithium ion batteries. Disordered carbons were synthesized by ball milling natural graphite in air. The composite was prepared by mixing the ball-milled graphite with petroleum pitch powder, pelletizing the mixture, and pyrolyzing the pellets at $1200^{\circ}C$ in an argon flow. The ballmilled graphite consists of distorted nanocrystallites and amorphous phases. In the composite particle, nanosized flakes are uniformly distributed in a soft carbon matrix, as revealed by X-ray diffractometer (XRD) and transmission electron microscopy (TEM) experiments. The composite is compatible with a pure propylene carbonate (PC) electrolyte and shows high rate capability and excellent cycling performance. The electrochemical properties are comparable to those of hard carbon.