• Fibers and Polymers
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• 제1권2호
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• pp.97-102
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• 2000

Pitch precursors were synthesized from coal tar(CT) and pyrolysis fuel oil(PFO, petroleum residue oil) at relatively low temperature of $250^{\circ}$, in the presence of horontrifluorideidiethyletherate complex(BFDE) as a catalyst and nitrobenzene(NB) as a co-catalyst. The softening point, nitrogen content and carbon yield increased with an increase of concentration of NB. The pitch precursors with good spinnability were prepared by removing the volatile components through $N_2$ blowing. The precursor pitches were spun through a circular nozzle, stabilized at $310^{\circ}$ and finally carbonized at $1000^{\circ}$. The optically anisotropic structure formed at the absence of NB was changed into isotropic structure, showing a decrease in size of the flow domain. The hollow carbon fiber could be prepared in the process of stabilization. The results proposed that the morphology of carbon materials could be controlled by changing the concentration of catalyst and/or co-catalyst and/or stabilization condition that affect on the mobility of molecules during carbonization.

• 한국결정성장학회지
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• 제3권1호
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• pp.1-11
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• 1993

초크랄스키 법에 의한 실리콘 단결정 성장시 액상내의 난류 특성 억제 및 산소, 첨가제 등의 제어를 위해 보통 자기장을 걸어주고 있으며 본 연구에서는 축방향 자기장을 걸어주었을 경우 나타나는 자장의 효과를 수치적으로 계산하였다. 자기력의 증가에 따라 액상내의 유속의 크기는 상당히 억제되었다. 자장의 크기가 증가함에 따라 중심축 부근에서 상승하는 유동의 속도가 감소하기 때문에 S/L 응고계면은 점점 평탄해졌으며, B=0.3 Tesla에서 액상내의 온도 분포는 중심축 부근을 제외하고는 오직 전호 효과로만 계산된 결과와 거의 유사하였다. 또한 고상 및 액상 표면을 통한 열방출량 중 Ar 가스에 의한 열방출량은 3% 미만이었으며 대부분의 열량은 복사를 통해 방출되었다.

• 국제초고층학회논문집
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• 제1권2호
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• pp.107-116
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• 2012

The overarching objective of this study is to predict the convective heat transfer around a human body under forced strong airflow conditions assuming a strong wind blowing through high-rise buildings or an air shower system in an enclosed space. In this study, computational fluid dynamics (CFD) analyses of the flow field and temperature distributions around a human body were carried out to estimate the convective heat transfer coefficient for a whole human body assuming adult male geometry under forced convective airflow conditions between 15 m/s and 25 m/s. A total of 45 CFD analyses were analyzed with boundary conditions that included differences in the air velocity, wind direction and turbulence intensity. In the case of approach air velocity $U_{in}=25m/s$ and turbulent intensity TI = 10%, average convective heat transfer coefficient was estimated at approximately $100W/m^2/K$ for the whole body, and strong dependence on air velocity and turbulence intensity was confirmed. Finally, the formula for the mean convective heat transfer coefficient as a function of approaching average velocity and turbulence intensity was approximated by using the concept of equivalent steady wind speed ($U_{eq}$).

• Elastomers and Composites
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• 제50권4호
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• pp.297-303
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• 2015

Ammonium polyphosphate-polyurethane foam composite (APP-PUF) was prepared from poly(adipate)diol/ammonium polyphosphate composite (f = 2), polyether polyol (f = 4.6), and PMDI (f = 2.5). As a blowing agent, $H_2O$ was used at various concentrations. The thermal decomposition behavior, morphology, closed-cell content, and density of APP-PUF were characterized. At the $H_2O$ concentrations lower than 3.5 php, the cell size of pure polyurethane foams (PUF) and APP-PUFs were close each other. As the $H_2O$ concentration became greater than 5.0 php, the cell size of the PUFs greatly increased compared to that of APP-PUFs. Addition of 1.5~1.9 wt% ammonium polyphosphate to the PUFs greatly enhanced the thermal stability of the PUFs, so 50 wt% residual temperature of APP-PUFs increased to $380{\sim}488^{\circ}C$, which were $30{\sim}70^{\circ}C$ higher than those of the PUFs. Thermal stability of the PUFs and APP-PUFs increased with $H_2O$ content and then decreased once $H_2O$ content exceeded 5 php.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 춘계학술대회 논문집 전기설비전문위원
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• pp.173-175
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• 2004

The degree of contamination on outdoor insulators is one of the most importance factor to determine the pollution level of outdoor insulation. Outdoor insulators in coastal are affected due to salty wind blowing from the seaside. The sea salt is known as the most dangerous pollutant. As known through the preceding study, the generation of salt pollutant and the pollution degree of outdoor insulators have a close relation in accordance with meteorological conditions, such as temperature, humidity, dewpoint, wind velocity and wind direction. Therefore, at first, we have analyzed relation between meteorological conditions and contaminants for development of prediction method. In this paper, we have investigated a statistical estimation technique based on actual data for equivalent salt deposit density(ESDD) of outdoor insulators which were installed in Kochang field test substation with multiple linear regression analysis.

• 한국지구과학회지
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• 제39권6호
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• pp.555-567
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• 2018

본 연구에서는 서해 연안에서의 실측-위성 해수면온도 차이를 규명하고 그 특성을 분석하기 위해 GCOM-W1/AMSR2 마이크로파 해수면온도 자료와 서해 연안에 위치한 덕적도, 칠발도, 외연도 해양기상 부이의 실측 수온 자료를 활용하여 2012년 7월부터 2017년 12월까지 총 6,457개의 일치점 자료를 생산하였다. 5년 이상의 덕적도, 칠발도, 외연도 해양 부이 수온 자료와 AMSR2 해수면온도를 비교하여 정확도를 제시하였다. 마이크로파 위성 해수면온도와 현장 관측 부이 해수면온도 간의 차이는 풍속과 수온 등 환경 요인에 대한 의존성을 가지는 것으로 나타났다. 낮시간 풍속이 약할 때 ($<6ms^{-1}$) AMSR2 해수면온도는 실측 해수면온도보다 높게 산출되며, 밤시간에 대해서는 풍속이 커질수록 양의 편차가 증가함을 밝혔다. 또한 AMSR2 해수면온도와 실측 해양부이 수온 간의 차이가 증가하는 경향은 낮은 온도에서 마이크로파 센서의 민감도의 저하와 육지에 의한 자료오염과 관련이 있는 것으로 나타났다. 실측-위성 해수면온도 차이를 월별로 도시해본 결과, 마이크로파 위성 해수면온도의 편차는 강한 바람이 부는 겨울철에 가장 커진다고 알려져 있던 기존의 경향성과는 달리 덕적도, 칠발도 부이에서는 여름철 가장 큰 해수면온도 편차값이 나타났다. 이러한 차이는 부이의 위치에 따른 조석 혼합의 공간적 차등에 기인한 것으로 사료된다. 본 연구는 인공위성 합성장에 기여도가 높은 마이크로파 위성 해수면온도를 사용할 때 한반도 서해안에서 발생할 수 있는 문제점과 제한점을 제시하였다.

• 한국버섯학회지
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• 제20권3호
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• pp.127-137
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• 2022

느타리 균상 패널재배사에 상향과 하향 등 양방향으로 바람 토출이 가능한 정역 제어 대류팬(시험구)과 상향으로만 바람을 토출하는 관행 유동팬(대조구)을 이용한 경우에 대하여 내부환경과 버섯품질을 조사하였다. 재배 주기별 첫 수확 2일 전의 기온과 상대습도 편차를 조사한 결과, 시험구(1주기: 1.0-1.3℃와 7.8-9.0%, 2주기: 0.7-1.1℃와 10.0-11.4%)가 대조구(1주기: 5.8-6.4℃와 21.3-23.1%, 2주기: 3.4-5.7℃와 14.6-18.3%)보다 공기 균일도가 향상된 것으로 나타났다. 버섯품질의 경우 재배 주기에 따라 다소 차이를 보였는데 배지 세력이 큰 1주기에서는 정역 제어 대류팬을 적용시킨 경우가 관행 유동팬 적용에서보다 버섯품질이 다소 우수하였으나 배지 세력이 다소 약해진 2주기에서는 다소 떨어지는 것으로 나타났다. 2주기에서 공기 균일도가 향상되었음에도 버섯품질이 다소 떨어진 것은 하향으로의 바람이 버섯 생육에 영향을 주었기 때문인 것으로 판단되었다. 향후 균상 재배단 내측과 외측에서의 풍속 계측이 필요할 것으로 판단되었으며 정역 제어 대류팬의 운영 매뉴얼이 필요할 것으로 판단되었다.

• 대한기계학회논문집B
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• 제21권7호
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• pp.849-861
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• 1997

In this study, the effect of hole geometry of the cooling system on the flow and temperature field was numerically calculated. The finite volume method was employed to discretize the governing equation based on the non-orthogonal coordinate with non-staggered variable arrangement. The standard k-.epsilon. turbulence model was used and also the predicted results were compared with the experimental data to validate numerical modeling. The predicted results showed good agreement in all cases. To analyze the effect of the discharge coefficient for slots of different length to width, the inlet chamfering and radiusing holes were considered. The discharge coefficient was increased with increment of the chamfering ratio, radiusing ratio and slot length to width and also the effect of radiusing showed better result than chamfering in all cases. In order to analyze the difference between the predicted results with plenum region and without plenum region, the velocity profiles of jet exit region for a various flow conditions were calculated. The normal velocity components of jet exit showed big difference for the low slot length to width and high blowing rate cases. To analyze the flow phenomena injected from a row of inclined holes in a real turbine blade, three dimensional flow and temperature distribution of the region including plenum, hole and cross stream with flow conditions were numerically calculated. The results have shown three-dimensional flow characteristics, such as the development of counter rotating vortices, jetting effect and low momentum region within the hole in addition to counter rotating vortex structure in the cross stream.

• 한국해양공학회지
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• 제31권6호
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• pp.413-418
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• 2017

In the present study, silica-aerogel-polyurethane foams were synthesized to improve the mechanical characteristics and insulation performance of the polyurethane foam applied to a liquefied natural gas carrier at a cryogenic temperature of $-163^{\circ}C$. A silica-aerogel-polyurethane foam bulk was prepared using a homogenizer by varying the weight ratio of the silica aerogel (0, 1, 3, and 5 wt%), while maintaining the contents of the polyol, isocyanate, and blowing agent constant. Compression tests were performed at room and cryogenic temperatures to compare the mechanical properties of the silica-aerogel polyurethane foams. The internal temperature of the universal testing machine was maintained through the cryogenic chamber. The thermal conductivity of the silica-aerogel-polyurethane foam was measured using a heat flow meter to confirm the insulation performance. In addition, the effect of the silica aerogels on the cells of the polyurethane foam was investigated using FE-SEM and FTIR. From the experimental results, the 1 wt% silica aerogel polyurethane foam showed outstanding mechanical and thermal performances.

• 한국의류학회지
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• 제23권1호
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• pp.30-41
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• 1999

This study was conducted to verify the advantages of Gal-Ot. Gal-Ot is defined the clothings dyed with persimmon juice. Firstly the physical properties of fabrics were examined. Secondly the wear tests were conducted. The wear tests were performed in climatic chamber controlled 3$0^{\circ}C$ air temperature 50$\pm$5% R.H and 0.2m/s air movement. Four women subjects participated in this experiment and 4 times experiments were performed per one subject. The expeimental schedule was planned following 4 steps that is sedentary posture during 30 minutes-walking the 5。slope treadmill by 70m/min during 20 minutes-sedentary posture during 20 minutes-standing posture on toward the blowing wind during 10 minutes. The results obtained is as folows : The insulation of fabric was increased with dyeing with persimmon juice. The air permeability of fabric was remarkably increased with dyeing with persimmon juice. The mean skin temperatures of subjects were apt to be higher in wearing Gal-Ot than undyed clothing. The clothing micro temperature of subjects were slightly inclined to become lower in wearing Gal-Ot than undyed clothing, The clothing micro humidity was decreasee when: the subjects were gal-Ot than wore undyed clothing, And then it brought about more comfortable on wear sensation. The differences of physiological reactions were not consistent between clothing types except for sweat rate on the back. This result may be attributed the to complex experimental schdules consisted of four steps and to a little difference between open type and close type. However I consider that the clothing type of Gal-Ot is suitable for open type because Gal-Ot is summer wear for blocking the sultry heat.