• Journal of the Korean Institute of Gas
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• v.17 no.4
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• pp.33-38
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• 2013

A study was carried out on the effect of particle size (mean diameter) on magnesium dust explosion. Experimental investigations were conducted in a 20-L explosion sphere, using 10 kJ chemical ignitors. Explosion tests were performed with three different dusts having mean diameter (38, 142, $567{\mu}m$) and the dust concentrations were up to $2250g/m^3$. The lower explosion limits(LEL) of magnesium dusts were about $30g/m^3$ at $38{\mu}m$ and $40g/m^3$ at $142{\mu}m$. LEL tended to increase with particle size and this means that the explosion probability of magnesium dust decreased with increase of particle size. The maximum explosion presssure ($P_m$) and $K_{st}$ (Explosion index) decreased with the increase of particle size. For magnesium powder of $567{\mu}m$, however, the explosive properties were not observed in the 5 kJ ignition energy.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.556-560
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• 2010

자갈하상 산지하천의 주요 관심사는 소류사 크기 분포와 연계하여 하상재료의 이송에 대한 광범위의 기초자료 확보하는 것이다. 자갈 하상재료가 주를 이루는 강원영동지역 양양남대천의 산지 하천을 대상으로 하상재료를 조사하였다. 산지하천의 소류사 크기를 고려한 소류사 채집기를 설치하고, 호우 발생 이후 측정기에 포획된 소류사의 크기를 파악하기 위해 입도분포를 분석하였다. 두 개의 소류사 측정기는 지남교 지점에 유속이 빠른 우안과 유속이 상대적으로 느린 좌안에 각각 설치하였다. 산지하천 시험구간의 하상재료 분포도는 그림 1과 같으며, 하상재료 평균입경은 184.65mm 이였다. 연구단에서 운영중인 법수치 우량관측소의 관측자료에 따르면, 2009년 11월 1~13일 185mm 강우가 발생하였으며, 11월 11일 7:00경에 최대수위에 따른 첨두유출량 107.23$m^3/s$가 발생하였다. 첨두유출 발생당시 이동한 우안 소류사의 평균입경은 102.88mm 이였고, 좌안 소류사의 평균입경은 66.53mm 이였다(그림 2). 하상재료의 평균입경에 대한 소류사 평균입경을 비교하였을 때, 소류사는 하상재료의 $45.87{\pm}13.92%$ 크기 범위에서 이동함을 확인하였다.

• Journal of the Korean Institute of Gas
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• v.16 no.5
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• pp.7-13
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• 2012

An experimental study has been done to investigate the explosion characteristics of aluminum powders with different sizes and concentrations in a 20 L spherical explosion vessel. Two different sizes of aluminum powder were used : $15.1{\mu}m$ and $34.8{\mu}m$ with a volume mean diameter. The results revealed that $15.1{\mu}m$ Al powder has a Lower explosion limit (LEL) of $40g/m^3$, a maximun explosion pressure ($P_{max}$) of 9.8 bar and a maximum rate of pressure rise ($[dP/dt]_{max}$) of 1852 bar/s, in $34.8{\mu}m$ Al powder, LEL of $70g/m^3$, $P_{max}$ of 7.9 bar and $[dP/dt]_{max}$ of 322 bar/s. The LEL of Al powders tended to increase with the increase of particle size. Also, it was found that the flame velocity calculated from the powder with $15.1{\mu}m$ was about 5 times higher than that of the powder of $34.8{\mu}m$.

• Polymer(Korea)
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• v.30 no.6
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• pp.505-511
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• 2006

We tried to prepare polystyrene composite particles containing carbon black by suspension polymerization with water as a reaction medium. Hydrophobic silica was selected as a stabilizer and oil-soluble azobisisobutyronitrile (AIBN), as an initiator. All polymerization reactions were carried out at a fixed temperature of $75^{\circ}C$. Stabilizer concentration was varied from $0.17{\sim}3.33wt%$ compared to water, where particles with $7.96{\mu}m$ in average diameter were obtained at 1.57 wt% of stabilizer. Increase in divinylbenzene concentration, as a crosslinking agent, from $0.1{\sim}1.0 wt%$ compared to monomer exhibited a large increase in average particle diameter Incorporation of 1wt% of carbon black compared to monomer produced an increase in average diameter It is speculated that viscosity lower than that necessary to induce even dispersion of carbon black particles led to poor dispersion, and as a result, large particles. For a styrene mixture containing 3 wt% carton black compared to monomer, enhanced dispersion due to an increase in carbon black concentration reduced average particle diameters. For styrene mixtures containing 1 and 3 wt% carbon black compared to monomer, preparticles before polymerization and polymer composite particles after polymerization showed a similar tendency towards particle formation. When carbon black concentration compared to monomer was increased to 5 and 7 wt%, styrene mixtures exhibited a large increase in viscosity and thus better dispersion of carbon black particles, which led to a decrease in preparticle diameters. However, these particles experienced agglomeration in the polymerization process, and polystyrene composite particles increased in average diameter.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.252-252
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• 2022

최근 기존의 전통적인 부유사채집기를 활용한 유사량 측정방법의 대안으로 지속적인 유량측정을 목적으로 활용되고 있는 횡방향 초음파도플러유속계의 초음파산란도를 활용하여 부유사농도를 측정에 대한 연구가 수행되고 있다. 하지만, 하천에서 횡방향 초음파도플러유속계를 활용한 유사량 측정 연구는 현장에서 측정된 자료를 기반으로 분석이 수행되기 때문에 통제된 유사 조건에서의 유사의 농도 및 입도분포에 대한 사전 정보를 바탕으로 정밀한 분석의 어려움이 있다. 이에 본 연구에서는 안동하천실험센터 순환수로에서 균일한 입도를 가지고 있는 황토를 활용하여 주입량에 따른 초음파산란도의 변화와 동시에 측정된 LISST(laser in-situ scattering and transmissometry)의 부유사 농도와 입도 자료를 활용하여 유사공급에 따른 3Mhz의 단일 주파수를 사용하는 횡방향 초음파도플러유속계의 초음파산란도를 활용한 부유사농도 및 평균입경의 측정에 대한 연구를 수행하였다. 측정결과, 유사공급에 따라서 초음파산란도를 활용하여 부유사농도가 증가하는 경향을 나타내고 있었으며, 횡방향 초음파도플러유속계로부터 측정된 셀별 초음파산란도를 활용하여 부유사농도의 공간적인 분포의 분석이 가능함을 확인할 수 있었다. 그리고 유사감쇄계수를 활용하여 LISST로부터 측정된 평균입경과의 관계식을 개발하여 유사공급에 따른 평균입경의 변화를 측정할 수 있을 것으로 나타났다. 추후, 통제된 조건에서의 다양한 입도분포에 따른 실험을 통해 횡방향 초음파도플러유속계의 초음파산란도를 활용한 부유사농도 측정 정확도를 개선과 유사감쇄계수를 통해 평균입경을 측정하는데 활용이 될 것으로 판단된다.

• Journal of Korea Water Resources Association
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• v.44 no.6
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• pp.449-459
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• 2011

By examining the experimental results, the critical mean velocity which initiates the movement of riprap is increased with the riprap size in mean diameter, the mean diameter over water depth (d/h), Froude number (Fr), and turbulent shear velocity over critical mean velocity (u*/${\nu}$) which have great correlations among them so these parameters are adopted governing hydraulic stability for riprap. The hydraulic stability equation for riprap is developed by regression analysis. The developed equation is expanded from 0.36~0.73 m/s of experimental range to 0~5.0 m/s for the application in engineering discipline. So many useful relations among those parameters including critical mean velocity are derived by expanding to high Reynolds regions. Mean diameter calculation results by expanding to high Reynolds regions coincide with the calculations of ASCE and USBR at the range of 0~3.0 m/s and the calculation result of ASCE at the range of 3.0~5.0 m/s. The results by developed formulae coincide well with the formulae of ASCE in general and also the results by recently developed existing formulae of hydraulic stability for riprap. Thus, the developed equation has the high applicability in engineering discipline to evaluate the hydraulic stability for riprap.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.334-334
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• 2017

Representative particle sizes(RPS) are commonly used for particle size distribution of heterogeneous sediment such as bed material. RPS can provide not only information of mean characteristics of sediment, but also other properties like sorting, skewness, kurtosis. For sediment including sand and clay material, RPS is estimated through two steps. The first is experimental step for calculating weight of each size class, the next is interpolation step to get RPS by using the graph plot. At the second step, graph method known as direct reading of value along the interpolation line in the graph plot is commonly used. This method is often time-consuming job. In this study we developed a new program to get RPS by using MS Excel. Simple linear and semi-log interpolation are used. When compared with conventional graph method(direct reading), simple linear shows 5.31%, while semi-log 1.29% of relative difference. We developed MS Excel program for estimation of RPS automatically.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.461-468
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• 2018

Microspheres were prepared by solvent-evaporation method with Poly-L-lactic acid (PLLA) as a starting material, and the effects of preparation variables on microsphere shape and average particle size were investigated. As the concentration of PVA solution increased from 1 to 5 wt%, the average particle size decreased from $370{\mu}m$ to $160{\mu}m$ and then increased to $240{\mu}m$ at 7 wt%. On the other hand, As the addition volume of PVA solution increased from 10 mL to 50 mL, the average particle size decreased from $370{\mu}m$ to $220{\mu}m$. Also, as the stirring speed increased from 500 rpm to 1,500 rpm, the average particle size decreased from $370{\mu}m$ to $110{\mu}m$. When dichloromethane and chloroform were used as organic solvents, respectively, the average particle size did not show any significant difference. However, when dichloromethane was used, voids were observed on the particle surface, but when chloroform was used, smooth spherical particles were obtained.

• Journal of Power System Engineering
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• v.2 no.1
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• pp.25-30
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• 1998

In order to investigate the droplet size distribution and Sauter Mean Diameter in a ultra high pressure diesel spray, fuel was injected with ultra high pressure into the environments of high pressure and room temperature by an Electronic Hydraulic Fuel Injection System. Droplet size was measured with the immersion liquid sampling technique. The immersion liquid was used a mixture of water-methycellulose solution and ethanol. The Sauter Mean Diameter decreased with increasing injection pressure, with a decrease environmental pressure (back pressure) and nozzle diameter. Increasing the injection pressure makes the fuel density distribution of the spray more homogeneous. An empirical correlation was developed among injection pressure, air density, nozzle diameter and the Sauter Mean Diameter of spray droplets.

• Journal of the Korean Geotechnical Society
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• v.21 no.7
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• pp.13-20
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• 2005

For experimental study on the effect of particle size distribution on the liquefaction resistance strength, particle size distribution curves of the dredged soil were investigated. In this process, four mean particle sizes and three uniformity coefficients were defined representatively and twelve representative particle size distribution curves which have different mean particle size and uniformity coefficient, were defined and manufactured by using the real dredged river soil. Cyclic triaxial tests and resonant column tests were carried out to analyze the effect of mean particle size and uniformity coefficient on the liquefaction resistance strength and dynamic characteristics.