• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.119-125
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• 2018

The particle based computational fluid dynamics (CFD) method, which follow Lagrangian approach for fluid dynamics, fluid particle behavior by tracking all particle calculation physical quantities of each particle. According to basic concept of particle based CFD method, it is difficult to satisfy continuum theory and measure influences from neighboring particle. Article number density and weight function were used to solve aforementioned issue. Difficulties continuum mean simulate non-continuum particles such as solid including granular and sand. In this regard, the particle based CFD method modified solid particle problems by replacing viscous and surface tension forces friction and drag forces. In this paper, particle interaction model for solid particle friction model implemented to simulate solid particle problems. The broken dam problem, which is common to verify particle based CFD method, used fluid or solid particles. The angle of repose was observed in the simulation results the solid particle not fluid particle.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.889-894
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• 1999

Preparation of micron size polymer particles which have desired morphology, size, and structure by emulsion polymerization is very difficult due to coagulation of latex particles and formation of second generation particles. But there are attractive merits such as preparation of structural and functional polymer particles in seeded emulsion polymerization. Seeded emulsion polymerization of n-butyl acrylate(BA) was carried out to investigate the effects of stirring rate, reaction temperature, concentration of initiator, emulsifier, and cross-linking agent on the particle size and size distribution. By the combination of suitable reaction conditions, we succeeded in preparing $0.14{\sim}3.67{\mu}m$ diameter of poly(n-butyl acrylate)(PBA) particles using sequential seeded emulsion polymerization.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.35-44
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• 2013

In this study, a particle method without using grid was applied for analysing large deformation problems in soil flows instead of using ordinary finite element or finite difference methods. In the particle method, a continuum equation was discretized by various particle interaction models corresponding to differential operators such as gradient, divergence, and Laplacian. Soil behavior changes from solid to liquid state with increasing water content or external load. The Mohr-Coulomb failure criterion was incorporated into the particle method to analyze such three-dimensional soil behavior. The yielding and hardening behavior of soil before failure was analyzed by treating soil as a viscous liquid. First of all, a sand column test without confining pressure and strength was carried out and then a self-standing clay column test with cohesion was carried out. Large deformation from such column tests due to soil yielding or failure was used for verifying the developed particle method. The developed particle method was able to simulate the three-dimensional plastic deformation of soils due to yielding before failure and calculate the variation of normal and shear stresses both in sand and clay columns.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.471-476
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• 1986

본 연구에서는 구모양의 석탄가루나 곡식가루등 비금속성 고체입자가 압축파 (shock wave)에 의해 생성된 고온의 기체속에 놓여있을때 일어나는 점화현상을 활성 화에너지(activation energy)가 큰 경우의 접합 점근법을 이용 해석하였다. 이렇게 하여 얻어진 석탄입자에 대한 점화지연시간을 실험치와 비교 이의 타당성을 입증하였 다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.146.2-146.2
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• 2010

PEMFC를 구성하는 여러 부품 중 핵심부품은 MEA(Membrane Electrode Assembly)으로서 실제 연료전지 반응이 일어나며 연료전지의 성능을 결정하는 부품이다. 그러나 PEMFC의 특성 상 촉매로 귀금속인 Pt가 사용됨에 따라 경제성이 확보된 MEA의 성능을 얻기 위해선 현재 Pt 담지량을 0.3mg/$cm^2$ 이하로 크게 감소시키면서 Pt촉매의 고분산화와 미반응 사이트의 감소가 필요하다. 본 연구에서는 Pt 촉매의 미반응 사이트를 줄이고자 전기영동법에 의해 카본전극(carbon black + GDL) 상에 Pt 나노입자를 직접 석출시켜 Pt/C 촉매 전극을 제조 하였다. 본 실험에서는 가장 좋은 Pt 나노입자의 석출거동을 나타낸 30mA/$cm^2$, pH 2, duty cycle 25% 조건을 기준으로 하여 electro-deposition time을 통한 석출량 제어와 carbon paper의 wet proofing 정도에 따른 Pt의 석출거동을 조사하였으며, 종래의 방법으로 제조한 Pt/C 촉매전극의 전기화학적 특성과 비교 분석하였다. 전기영동 석출법에 사용된 Pt나노입자는 $H_2PtCl_6{\cdot}6H_2O$로부터 화학적 환원법으로 합성한 2~3nm 입경을 갖는 Pt콜로이드를 사용하였으며, magnetic stirring과 항온 ($20^{\circ}C$)을 유지하여 실험하였다. 전기영동 석출량 제어는 electro-deposition time을 5~25분까지 5분 간격으로 나누어 실험하였고 카본전극을 구성하는 carbon paper의 wet proofing 정도가 Pt 나노입자 석출거동에 미치는 영향을 조사하기 위하여 20, 40, 60%의 서로 다른 wet proofing 값을 갖는 carbon paper를 사용하여 Pt/C 촉매 전극을 제조하였다. 전기영동법으로 석출된 카본블랙 전극 상 Pt나노입자의 분산도와 담지량는 각각 FE-SEM과 TGA 장비를 사용하여 측정하였고, 제조된 Pt/C 촉매 전극의 전기화학적 촉매 특성은 cyclic voltammetry(CV)법으로 측정하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.86.2-86.2
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• 2011

저온형 연료전지인 직접 메탄올 연료전지(Direct Methanol Fuel Cells, DMFC)는 친환경적인 발전 시스템, 높은 에너지 효율의 장점 때문에 주목을 받고 있으나 연료극의 촉매로 사용되는 금속은 고가의 귀금속인 Pt와 Ru가 요구되어 제조비용이 비싸기 때문에 촉매의 양을 줄이고, 반응 도중 생성되는 CO에 의한 촉매의 피독 문제 등 해결하여야 할 점이 산적해 있어 연료전지 중 촉매의 활성을 높이는 연구들이 활발히 이루어지고 있다. 종래의 MEA의 촉매층 제조공정은 우선 환원석출법에 의해 Pt-Ru/C를 합성하고 Nafion 용액에 혼합하여 Pt-Ru/C 슬러리를 제조한다. 이 방법에서는 carbon sheet에 spray 방법으로 Pt-Ru/C 촉매층이 만들어지기 때문에, Pt-Ru 촉매가 Nafion에 의해 부분적으로 매몰되어 촉매의 전기화학적 활성이 떨어지는 문제점이 있다. 이를 해결하는 방안으로 펄스전류를 이용하여 Pt-Ru 합금입자를 carbon sheet에 전기화학적으로 담지 시켜 Nafion에 매몰되는 것을 방지하는 펄스전해법 연구가 진행되고 있다. 그러나 촉매의 입자크기가 일반적으로 50~70 nm 이상으 크기 때문에 촉매의 낮은 활성이 문제점으로 야기되고 있다. 본 연구에서는 Pt-Ru/C 촉매층 제조 문제점을 해결하고, 촉매의 전기화학적 활성을 증가시키기 위해서 2~4 nm Pt-Ru 콜로이드를 전해액으로 사용하고, 전기영동법을 이용하여 Pt-Ru 나노 입자를 carbon sheet($1{\times}1cm^2$) 에 담지 시켰다. 전기영동법에서 균일한 Pt-Ru 촉매층의 제조를 위해 전류인가 방법으로는 펄스전류를 사용하였고, 실험변수로는 전해액 pH, duty cycle, 담지시간을 선정하였다. 합성된 Pt-Ru 콜로이드를 TEM분석으로 나노입자의 크기와 분산성 분석하였고, 콜로이드 나노입자의 표면전하 상태를 분석하기 위해 zeta-potential을 분석하였다. Pt-Ru/C의 촉매의 전기화학적 활성을 분석하기 위하여 0.5 M H_2SO_4$ 와 1 M $CH_3OH$ 혼합용액에 CV(Cyclic Voltammetry)실시하였고, carbon sheet 전극 상 Pt-Ru의 분산성 확인을 위하여 FE-SEM분석을 수행하였다.

• Analytical Science and Technology
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• v.28 no.1
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• pp.33-39
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• 2015

CdS-QD particles are a nano-sized semiconducting crystal that emits light. Their optical properties show great potential in many areas of applications such as disease-diagnostic reagents, optical technologies, media industries and solar cells. The wavelength of emitting light depends on the particle size and thus the quality control of CdS-QD particle requires accurate determination of the size distribution. In this study, CdS-QD particles were synthesized by a simple ${\gamma}$-ray irradiation method. As a particle stabilizer polyvinyl pyrrolidone (PVP) were added. In order to determine the size and size distribution of the CdS-QD particles, sedimentation field-flow fractionation (SdFFF) was employed. Effects of carious parameters including the the flow rate, external field strength, and field programming conditions were investigated to optimize SdFFF for analysis of CdS-QD particles. The Transmission electron microscopy (TEM) analysis show the primary single particle size was ~4 nm, TEM images indicate that the primarty particles were aggregated to form secondary particles having the mean size of about 159 nm. As the concentration of the stabilizer increases, the particle size tends to decrease. Mean size determined by SdFFF, TEM, and dynamic light scattering (DLS) were 126, 159, and 152 nm, respectively. Results showed SdFFF may become a useful tool for determination of the size and its distribution of various types of inorganic particles.

• Applied Chemistry for Engineering
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• v.7 no.2
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• pp.393-400
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• 1996

The conducting polymer composites were prepared by imbibing the porous particle with an $FeCl_3$ oxidant solution, drying the imbibed porous particle, and imbibing again with pyrrole solution for polymerization to take place in the pore. The conductivity of the porous composite particles, was higher than that of nonporous particles. Also, the conductivity of composite was increased with increasing specific surface area and pore specific volume of the host porous particles since the degree of formation of conducting polymer in the pore increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.7
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• pp.455-462
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• 2017

The magnetic interaction between elliptic Janus magnetic particles are investigated using a direct simulation method. Each particle is a one-to-one mixture of paramagnetic and nonmagnetic materials. The fluid is assumed to be incompressible Newtonian and nonmagnetic. A uniform magnetic field is applied externally in a horizontal direction. A finite-element-based fictitious domain method is employed to solve the magnetic particulate flow in the creeping flow regime. In the magnetic problem, the magnetic field in the entire domain, including the particles and the fluid, is obtained by solving the governing equation for the magnetic potential. Then, the magnetic forces acting on the particles are calculated via a Maxwell stress tensor formulation. In a single particle problem, it is found that the orientation angle at equilibrium is affected by the aspect ratio of the particle. As for the two-particle interaction, the dynamics and the final conformation of the particles are significantly influenced by the aspect ratio, the orientation, and the spatial positions of the particles. For the given positions of the particles, the fluid flow is also influenced by the orientation of each particle. The self-assembly structure of the particles is not a fixed one, but it varies with the above-mentioned factors.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.04a
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• pp.325-327
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• 2000

본 연구에서는 한반도의 청정지역인 제주도 고산과 한라산 1100 고지에서의 입자상 물질을 분석하였다. 입자상 물질을 분석하는 방법 중에 EPMA(Electron Probe X-ray Microanalysis)를 이용한 단일 입자 분석법(Single Particle Analysis)은 개개 입자의 형상과 크기 그리고 화학 조성에 대한 정보를 동시에 제공하기 때문에 개개 입자의 생성, 이동, 반응성, 소멸 그리고 환경에의 영향에 대한 자세한 정보를 얻을 수 있다. (중략)