• 한국도로학회논문집
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• 제19권4호
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• pp.37-44
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• 2017

PURPOSES : Conductive and convective heat transfer simulations for an asphalt mixture were made by using discrete element method (DEM) and similarity principle. METHODS : In this research, virtual specimens composed of discrete element method particles were generated according to four different predetermined particle size distribution curves. Temperature variations of the four different particles for a given condition were estimated and were compared with measurements and analytical solutions. RESULTS : The virtual specimen with mixed particles and with the smallest particle show very good agreement with laboratory test results and analytical solutions. As particle size decreases, better heat transfer simulation can be performed due to smaller void ratio and more contact points and areas. In addition, by utilizing the similarity principle of thermal properties and corresponding time unit, analytical time can be drastically reduced. CONCLUSIONS : It is concluded that the DEM asphalt mixture specimens with similarity principle could be used to predict the temperature variation for a given condition. It is observed that the void ratio has critical effect on prediction of temperature variation. Comparing the prediction for a 4 mm particle specimen with a mixed particle specimen, it is also concluded that predicting the mixed particle specimen temperature is much more efficient considering the number of particles that are directly associated with computational time in DEM analysis.

• 산업기술연구
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• 제23권A호
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• pp.175-179
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• 2003

A study on the particle growth in $TEOS/O_2$ plasma was performed by observing the particle size and its morphology by TEM. The qualitative chemical analysis of particles was also determined by the EDS (Energy Dispersive X-Ray Spectrometer). The effects of process variables such as the plasma on-time and bubbler temperature on the particle growth were investigated. The particle size becomes larger as the plasma on-time because of the longer coagulation, and also as the bubbler temperature increases because of the faster coagulation between particles.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1203-1206
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• 2005

Electron temperature and plasma density in coplanar alternating-current plasma display panels (AC-PDP's) have been experimentally investigated in accordance with discharge time by a micro-probe in this experiment. The resolution of a step mortor to move in micro-Langmuir probe is 10um.[1-3] The used gas in this experiment is He-Ne-Xe (4%) mixure gas. And sustain voltage is 320V which is above of firing voltage for degradation. The electron temperature and plasma density can be obtained from current-voltage (I-V) characteristics of micro Langmuir probe, in which negative to positive bias voltage was applied to the probe. And Efficiency is calculated by formula related discharge power and light emission. Those experiments operated as various discharge time ($0{\sim}72$ Hours). As a result of this experiment, Electron Temperature was increased from 2eV to 5eV after discharge running time of 20 hours and saturates beyond 20 hours. The plasma density is inversely proportional to the square root of electron temperature. So the plasma density was decreased from $1.8{\times}10^{12}cm^{-3}$ to $8{\times}10^{11}cm^{-3}$ at above discharge running time. And the Efficiency was reduced to 70% at 60hours of discharge running time.

• 한국세라믹학회지
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• 제37권7호
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• pp.638-644
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• 2000

The sintering behaviors of the glass-alumina composites for low firing temperature were investigated as functiions of the volume fraction of alumina powder and the particle size with respect to porosity and pore shape. As the volume fraction of alumina powder was increased or the particle size of it was decreased, the sintering temperature of open pore-closing was raised. When the volume fractions of alumina which had 2.19$\mu\textrm{m}$ median diameter were increased with 20, 30, 40, and 50%, the sintering temperatures of open pore-closing were 425, 450, 475, and 500$^{\circ}C$. And when the median particle size of alumina was diminished from 2.19$\mu\textrm{m}$ to 0.38$\mu\textrm{m}$, the sintering temperature of open pore-closing was increased from 450$^{\circ}C$ to 475$^{\circ}C$. Especially, the sintering temperature, which showed maximum density, was corresponded with the stage of open pore-closing and after achieving maximum density over heating resulted in dedensification of specimen, so called, over-firing behavior.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.157-163
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• 2011

마그네슘 입자 군 연소 실험 장치를 제작하고 연소 실험을 수행하였다. 예혼합 화염용 버너에서 마그네슘 입자의 공급 질유량을 변화시켰을 때 점화 지연시간의 변화를 확인하였다. 마그네슘의 질량유량을 증가시킴에 따라 점화 지연시간이 단축됨을 확인하였다. 또한 마그네슘 입자 크기 별, 혼합비에 따라 변화시켰을 군 연소 화염 온도를 two wavelength pyrometry 를 이용하여 군 연소 화염온도를 측정하였다. 입자 크기별 군 연소 화염온도는 거의 비슷함을 확인 할 수 있었으며, 당량비에 따른 화염온도의 측정을 통해 연소되는 마그네슘 연소화염 분포의 특성을 알 수 있었다.

• 한국결정성장학회지
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• 제17권1호
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• pp.11-17
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• 2007

The spherical NiZn ferrite particles were prepared by ultrasonic spray pyrolysis with mixed solution of aqueous metal nitrates. The NiZn ferrite particle was observed with nano-sized primary particles of about 10 nm or less before annealing which represented as paramagnetic behavior measured at 77 K and room temperature. The typical abnormal growth of primary particles like polyhedral primary particles was observed by annealing at 1273 K with Zn-concentration dependency. The XRD patterns showed good crystallinity of NiZn ferrite powder after annealing. In annealing process, the intra-particle sintering phenomenon was observed and the spherical particle morphology was collapsed at 1673 K. The saturation magnetization of NiZn ferrite powder for each annealing temperature was decreased with measuring temperature of $77{\sim}$300K.

• 한국주조공학회지
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• 제5권2호
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• pp.97-108
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• 1985

In order to investigate the effect of magnesia clinker on the characteristics of the investments, temperature change during setting, setting time, compressive strength and thermal expansion of the investments were measured, and x-ray analyses were also performed. The investments were prepared in accordance with variation of the content and the particle size of magnesia clinker respectively. From this experiment, the results were summarized as follows; 1. Temperature of the investments during setting rapidly increased with increase of MgO contents and decrease of the particle size of magnesia clinker. 2. Setting time decreased with increase of MgO contents and decrease of the particle size of magnesia clinker. 3. Compressive strength increased with increase of MgO contents and decrease of the particle size of magnesia clinker. 4. Thermal expansion decreased with increase of MgO contents and decrease of the particle size of magnesia clinker. From the above results, the investment which contains 8% of MgO (270-325mesh) could be recommended for phosphate investment castings.

• 대한기계학회논문집
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• 제18권11호
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• pp.3057-3065
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• 1994

An experimental study has been made for heat transfer and particle deposition during the Modified Chemical Vapor Deposition process which is currently utilized to manufacture high quality optical waveguides. The distributions of tube wall temperatures, rates and efficiencies of particle deposition were measured. Results indicate that the temperature distributions of the tube wall in the axial direction yield the quasi-steady form in which temperature distributions fit in one curve if the relative distance from the moving torch is used as an axial coordinate. Due to the repeated heatings from the traversing torch, the wall temperatures are shown to reach the minimum ahead of torch and it is shown that the two torch formulation suggested by Park and Choi is valid to predict this minimum temperature. Measured wall temperatures, particle deposition efficiencies and tapered entry length are compared with the previous modelling results and shown to be in agreement.

• 한국주조공학회지
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• 제5권2호
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• pp.85-96
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• 1985

In order to investigate the effect of particle size and distribution of silica sand on the characteristics of investment, W/P ratio, setting time, temperature change during setting, setting expansion, thermal expansion and compressive strength of the investments were measured. In this experiment, magnesia clinker and mono ammonium phosphate were used as binder, and particle size and distribution of silica sand were classified for convinence into 10 categories. The main results obtained from this investigation were summerized as follows. 1. W/P ratio decreased with increase of particle size and evenness in distribution of sand grain. 2. Setting time decreased with increase of evenness in distribution of sand grain, and temperature during setting increased with evenness in distribution of sand grain. 3. Setting expansion decreased with increase of particle size, while it increased with evenness in distribution of sand grain. 4. Thermal expansion decreased with increase of particle size. 5. Compressive strength increased with increase of particle size and evenness in distribution of sand grain. From above results, G.F.N. 250 sand which contains 30% of 50-100 mesh could be recommended for investment casting.

• 한국분무공학회지
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• 제16권1호
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• pp.37-43
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• 2011

The present study conducted computational simulation for multiphase flow in the flame spray coating process with commercially available Ni-Cr powders. The flows in a flame spray gun is characterized by very complex phenomena including combustion, turbulent flows, and convective and radiative heat transfer. In this study, we used a commercial computational fluid dynamics (CFD) code of Fluent (ver. 6.3.26) to predict gas dynamics involving combustion, gas and particle temperature distributions, and multi-dimensional particle trajectories with the use of the discrete phase model (DPM). We also examined the effect of particle size on the flame spray process. It was found that particle velocity and gas temperature decreased rapidly in the radial direction, and they were substantially affected by the particle size.