• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.418-418
• /
• 2012

Synthesis of nanocrystalline diamond powder was investigated via a gas-to-particle scheme using the hot filament chemical vapor deposition. Effect of substrate surface seeding by nano diamond powder, and that of the electrical conductance of the substrate were studied. The substrate temperature, methane content in the precursor gas, filament-substrate distance and filament temperature were $670^{\circ}C$, 5% methane in hydrogen, 10 mm and $2400^{\circ}C$, respectively. The powder formation by gas-to-particle mechanism were greatly enhanced by the substrate seeding by the nano diamond powder. It was attributed to the removal of the electrostatic force between the substrate and the seeded nano diamond particle by the thermal electron shower from the hot filament, via the depolarization of the substrate surface or the attached diamond powder and subsequent levitation into the gas phase to serve as the gas-phase nucleation site. The powder formation was greatly favoured by the conducting substrate relative to the insulating substrate, which proved the actual effect of the electric static force in the powder formation.

• Journal of Environmental Science International
• /
• v.32 no.12
• /
• pp.899-914
• /
• 2023

Various seeding materials for cloud seeding are being used, and sodium chloride powder is one of them, which is commonly used. This study analyzed the experimental results of multi-aircraft cloud seeding in connection with Republic of Korea Air Force (CN235) and KMA/NIMS(Korea Meteorological Administration/National Institute of Meteorological Sciences) Atmospheric Research Aircraft. Powdered sodium chloride was used in CN235 for the first time in South Korea. The analysis of the cloud particle size distributions and radar reflectivity before and after cloud seeding showed that the growth efficiency of powdery seeding material in the cloud is slightly higher than that of hygroscopic flare composition in the distribution of number concentrations by cloud aerosol particle diameter (10 ~ 1000 ㎛). Considering the radar reflectivity, precipitation, and numerical model simulation, the enhanced precipitation due to cloud seeding was calculated to be a maximum of 3.7 mm for 6 hours. The simulated seeding effect area was about 3,695 km², which corresponds to 13,634,550 tons of water. In the precipitation component analysis, as a direct verification method, the ion equivalent concentrations (Na⁺, Cl^-, Ca²⁺) of the seeding material at the Bukgangneung site were found to be about 1000 times higher than those of other non-affected areas between about 1 and 2 hours after seeding. This study suggests the possibility of continuous multi-aircraft cloud seeding experiments to accumulate and increase the amount of precipitation enhancement.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2007.05a
• /
• pp.836-840
• /
• 2007

Large-Scale Particle Image Velocimetry (LSPIV)는 Particle Image Velocimetry (PIV)를 자연하천이나 실험실에서 넓은 영역($4m^2{\sim}45,000m^2$)에 적용할 수 있도록 확장시킨 것으로 지난 10여년 이상 세계적으로 널리 이에 대한 연구가 진행되고 있다. PIV는 seeding, illumination, recording 그리고 image processing으로 구성된다. LSPIV(Large Scale PIV)는 PIV의 기본원리를 근거로 하여 기존의 PIV에 비하여 실험실 내에서의 수리모형실험이나 일반 하천에서의 유속측정과 같은 큰 규모의 흐름해석을 할 수 있도록 seeding, illumination에 대한 조정이 필요하고, 촬영된 image에 대한 왜곡을 없애는 작업이 필요하다. LSPIV는 PIV의 네가지 단계를 포함하여 seeding, illumination, recording, image transformation, image processing 및 post-processing의 여섯 단계로 구성되어진다 (Li, 2002). LSPIV를 일반 하천에 적용시, 자연발생적인 tracers - 난류로 인한 표면 교란, 부유물, 수공구조물로 인해서 발생하는 자연 발생되는 거품 - 가 풍부해서 seeding이 불필요한 경우를 제외하고는 정확한 유속장의 해석을 위하여 인공적인 seeding을 필요로 한다. 일반적으로 Seeding 재료로 많이 이용되는 것은 wood mulch, Ecofoam, grain-straw 등이다. 하천에서 자연발생적 혹은 인위적 seeding을 하였을 때 이들 tracers의 물리적인 속성으로 바람에 쉽게 영향을 받고 이로 인하여 실제의 물표면유속을 대표하지 못하는 경우가 있다. 이에 실험실의 개수로에서 여러 가지 이용 가능한 tracers에 대하여 바람에 의한 오차 발생의 정도를 조사하였다. 실험에 사용된 seeding 재료로는 black polypropylene, Ecofoam, white polystyrene의 세가지를 이용하였다. black polypropylene (SG=0.92)과 white polystyrene (SG=0.0125)은 폭 1 m 이내의 개수로 실험 장치에서 유속장의 해석에 많이 이용되고 Ecofoam (SG=0.0065)은 수리 모형실험에서 많이 이용된다. seeding 물질에 따른 바람의 영향을 분석하기 위해서 폭 60cm의 개수로에서 seeding 물질을 변경하면서 펌프의 조작에 의해 3가지 단면평균유속을 발생시키고, 각 평균유속조건에 대해 4가지의 바람세기 - 바람이 없을 때와 팬의 바람세기를 1단, 2단, 3단으로 조정 - 를 발생시켰으며, 개수로위에서 촬영한 이미지의 상류측기준점으로부터 0.3556m 하류 지점을 횡단하는 단면의 표면유속을 측정하여 비교하였고, 그 단면의 중앙에서 물표면 바로 위 지점의 풍속을 측정하였다. 각 Seeding 물질에 대해 팬을 켜지 않았을 때, 즉 바람의 영향이 없을 때 측정한 표면유속을 바람의 세기가 변한 경우의 기준 표면유속으로 이용하였다. 본 연구의 결과 비중이 0.01 내외인 Ecofoam과 white polystyrene에 비해 비중이 0.92인 black polypropylene은 대부분이 물속에 잠겨 있어 흐름과 거의 일치하여 움직임을 알 수 있었다. 또한 흐름의 평균유속이 0.165 m/s의 저유속에서 바람이 tracers에 미치는 영향이 평균유속 0.558m/s인 경우보다 커서, 바람의 세기의 증가에 따라 표면유속 측정값이 급속히 감소되었다. 흐름의 평균유속이 큰 경우에는 바람이 tracer에 마치는 영향이 현격히 줄어듬을 보이고 있다. 결론적으로 유속이 증가함에 따라 바람의 영향은 감소하나, 바람의 영향을 최소화시키기 위해서는 가급적 비중이 큰 물질(0.5

• Proceedings of the Korean Society of Crop Science Conference
• /
• 2017.06a
• /
• pp.258-258
• /
• 2017

We received 73 wheat resources from CIMMYT for analysis of agricultural characteristics and qualities of them. We sowed 73 lines and 4 Korean varieties in fall and spring to compare differences of wheat traits between fall and spring seeding. The heading and maturity date of fall seeding lines has coming faster average 18 days than spring seeding lines. Fall seeding lines have more number of spike per $m^2$ and grain number of spike. Spike and awn length of spring seeding lines were shorter than fall seeding lines and stem length was variable to varieties in both condition. Protein contents of five of 73 lines, Jokyoung and Jopoom varieties decreased but the others increased. The sedimentation values of 34 lines include Jokyoung and falling number (F/N) of 44 lines include two varieties, Keumkang and Jokyoung, decreased but the others increased, respectively. Particle size was presented that most spring seeding lines were bigger. However, when it sowed in fall, the lightness (L) of wheat flour was lighter. Consequently, we confirmed when it was sowed in spring, agricultural traits and qualities of wheat got weak.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.04a
• /
• pp.64-64
• /
• 2002

Two dimensional velocity distributions outside a Mach 2.0 supersonic nozzle have been investigated using digital particle image velocimetry (PIV). Mean velocities, turbulence intensities, vorticity field and volume dilatation field are obtained from 300 instantaneous PIV images using 0.33 $\mu\textrm{m}$ $TiO_2$ particle. The seeding particle of larger size, 1.4 $\mu\textrm{m}$ $TiO_2$, is also used for the experimental measurements of velocity lag downstream of shock waves according to particle sizes. The results have been compared and analyzed with schlieren photographs and computational fluid dynamics (CFD) results for the velocity distribution, the locations of shock waves and over-expanded shock structure. It was shown that the locations of normal shock and shock waves can be resolved by the axial or radial velocities, and the velocity lag is more significantly increased due to particle inertia as a particle size increases. And it was also found that over-expanded shock structures call be predicted by volume dilatation fields, and streamwise turbulence intensities are influenced significantly by normal shock waves.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.8
• /
• pp.1078-1084
• /
• 2002

The formation temperature for the perovskite lead zirconate titanate [Pb(Zr,Ti)O3, PZT] derived from sol-gel route was lowered by more than $100^{\circ}C$ with the addition of crystallographically suitable seed particles, such as barium titanat e (BT) or PZT. We investigated the effect of seeding on the crystallization of perovskite phase and in the microstructure of the sol-gel derived PZT powder by varying the concentration, size and chemical species of seed particles. The phase transition as a function of temperature was monitored by DTA, XRD, and Raman spectroscopy, and the interface between the seed particle and grown PZT layer was analyzed by SEM and high resolution TEM techniques. It was found that both the heterogeneous and homogeneous nucleation contributes competitively in the formation of perovskite PZT grains.

• Journal of the Korean institute of surface engineering
• /
• v.53 no.5
• /
• pp.241-248
• /
• 2020

The change of the deposition behavior of diamond through a pretreatment process of the base metal prior to diamond deposition using HFCVD was investigated. To improve the specific surface area of the base material, sanding was performed using sandblasting first, and chemical etching treatment was performed to further improve the uniform specific surface area. Chemical etching was performed by immersing the base material in HCl solutions with various etching time. Thereafter, seeding was performed by immersing the sanded and etched base material in a diamond seeding solution. Diamond deposition according to all pretreatment conditions was performed under the same conditions. Methane was used as the carbon source and hydrogen was used as the reaction gas. The most optimal conditions were found by analyzing the improvement of the specific surface area and uniformity, and the optimal diamond seeding solution concentration and immersion time were also obtained for the diamond particle seeding method. As a result, the sandblasted base material was immersed in 20% HCl for 60 minutes at 100 ℃ and chemically etched, and then immersed in a diamond seeding solution of 5 g/L and seeded using ultrasonic waves for 30 minutes. It was possible to obtain optimized economical diamond film growth rates.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.11
• /
• pp.1503-1512
• /
• 2002

From the view of the environmental protection against the use of fossil fuels, a great of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative However the product species of the hydrogen flame is only $H_2O$, which emits only non-luminous radiation so the radiation from it is much smaller than that for a hydrocarbon flame. In this study, the authors designed and fabricated a laboratory scale test furnace to study thermal characteristics of hydrogen-air diffusion flame. In addition. the effects of addition of reacting as welt as non-reacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75 % was occupied by radiation while 25% by convection. When the aluminum oxide (Al$_2$O$_3$) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total as well as the radiative heat flux was increased when the carbon particles were seeded, since the overall temperature increased. The effects of swirl and excess air ratio were also examined.

• 한국연소학회:학술대회논문집
• /
• 2002.11a
• /
• pp.129-139
• /
• 2002

From the view of the environmental protection against the use of fossil fuels, a great of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative. However the product species of the hydrogen flame is only $H_2O$, which emits only non-luminous radiation so the radiation from it is much smaller than that for a hydrocarbon flame. In this study, the authors designed and fabricated a laboratory scale test furnace to study thermal characteristics of hydrogen-air diffusion flame. In addition, the effects of addition of reacting as well as non-reacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75% was occupied by radiation while 25 % by convection. When the aluminum oxide ($Al_2O_3$) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total as well as the radiative heat flux was increased when the carbon particles were seeded, since the overall temperature increased. The effects of swirl and excess air ratio were also examined.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.1779-1783
• /
• 2008

영상해석을 통한 흐름해석의 방법인 Large-Scale Particle Image Velocimetry (LSPIV)는 실험실내의 소규모 흐름해석에 이용하던 Particle Image Velocimetry (PIV)를 자연하천이나 실험실에서 넓은 영역($4m^2{\sim}45,000m^2$)에 적용할 수 있도록 확장시킨 것으로 지난 10여년전부터 세계적으로 널리 이에 대한 연구가 진행되고 있다. PIV는 seeding, illumination, recording 그리고 image processing으로 구성된다. LSPIV(Large Scale PIV)는 PIV의 기본원리를 근거로 하여 기존의 PIV에 비하여 실험실 내에서의 수리모형실험이나 일반 하천에서의 유속측정과 같은 큰 규모의 흐름해석을 할 수 있도록 seeding, illumination에 대한 조정이 필요 하고, 촬영된 image에 대한 왜곡을 없애는 작업이 필요하다. LSPIV는 PIV의 네 가지 단계를 포함하여 seeding, illumination, recording, image transformation, image processing 및 post-processing의 여섯 단계로 구성되어진다 (Li, 2002). LSPIV의 적용시 각 단계마다 유속계산시 오차를 발생시키는 27가지의 요인들이 존재하고 있는바 (Kim, 2006), 본 연구에서는 이들 중 실내의 실험실에서 파악이 가능한 인자들에 대해 그들 각각의 인자들이 유속 측정에 미치는 오차의 정도를 파악하고자 하였다. 본 연구에서는 LSPIV의 적용시 이용되는 이미지의 개수와 이미지 촬영시 적용된 이미지의 해상도에 따른 오차의 발생 정도를 조사하였다. 이미지 촬영에 있어서 비디오카메라를 이용할 경우 촬영시간에 따라 많은 수의 이미지를 취득할 수 있은바 이미지의 수에 따른 유속계산오차를 파악하고자 하였다. 또한 디지털 카메라를 이용할 경우 여러 가지 이미지 해상도를 이용할 수 있으므로 적용한 이미지 해상도에 따른 유속계산에 미치는 오차의 크기를 파악하고자 하였다. 이미지의 갯수가 유속계산시 미치는 오차의 영향의 정도를 조사하기 위해서 초당 30 frame을 촬영할 수 있는 비디오카메라를 이용하여 91초 동안 촬영된 이미지로부터 매 5번째의 이미지를 추출하여 455개의 이미지를 준비하였고 이로부터 이미지수를 10, 50, 100, 200, 300, 400의 순서로 증가시키면서 이미지 개수로부터 나타나는 유속계산 오차를 조사한 결과 이미지의 개수가 50매 이상인 경우는 이로 인한 오차가 1% 이하로 감소함을 파악하였다. 촬영된 이미지의 해상도가 유속계산시 미치는 영향을 조사하기 위해 디지털카메라를 적용하여 세가지 이미지 해상도(640*480, 1280*960, 2048*1536 pixel)로 변화시키면서 유속측정 오차를 분석한 결과 저해상도의 이미지를 이용한 경우 고해상도 이미지를 이용한 경우와 비교하여 3% 가량의 차이를 나타내었다.