• 한국가시화정보학회지
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• 제22권1호
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• pp.79-84
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• 2024

As microchips' degree of integration is getting higher, its cooling problem becomes important more than ever. One of the promising methods is using fractal microchannel heat sink by mimicking nature's Murray networks. However, most of the related works have been progressed only by numerical analysis. Perhaps such lack of direct experimental studies is due to the technical difficulty of the temperature and heat flux measurement in complex geometric channels. Here, we demonstrate the direct visualization of in situ temperature profile in a fractal microchannel heat sink. By using the temperature-sensitive fluorescent dye and a transparent Polydimethylsiloxane window, we can map temperature profiles in silicon-based fractal heat sinks with various fractal scale factors (a=1.5-3.5). Then, heat transfer rates and pressure drops under a fixed flow rate were estimated to optimize hydrodynamic and thermal characteristics. Through this experiment, we found out that the optimal factor is a=1.75, given that the differences in heat transfer among the devices are marginal when compared to the variances in pumping power. This work is expected to contribute to the development of high-performance, high-efficiency thermal management systems required in various industrial fields.

• 대한환경공학회지
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• 제22권3호
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• pp.511-521
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• 2000

디젤자동차와 같이 희박연소 상태에서 많이 배출되는 질소산화물을 선택적 촉매환원(SCR)으로 제거하기 위하여 제올라이트와 금속산화물을 조합한 촉매를 석영 반응로에서 설험하였다. 환원제는 자동차 배출가스에 포함되어 있어 실용 가능성이 크다고 판단되는 탄화수소 중 안전성 및 환원효율이 좋은 올레핀계 탄화수소인 프로필렌을 사용하였다. 본 연구에서는 제올라이트 및 금속산화물계의 단일촉매 상태에서의 NOx 전환율을 파악하고, 저옹 및 고온에서 활성이 다른 촉매를 기계적으로 조합하여 NOx 전환 활성 온도창(Temperature Window)을 확대하고 내구성이 좋은 촉매를 찾고자 하였다 0.55wt%Pt-$TiO_2$/5wt%Cu-ZSM-5 촉매와 0.28wt%Pt-$TiO_2$/$Al_2O_3$ 촉매 및 1.1 wt%Pt-$TiO_2$/$Mn_2O_3$ 촉매 모두 $400^{\circ}C$를 변곡점으로 저온과 고온에서 NOx 제거활성이 있었는데, 저온에서 활성이 가장 큰 것은 0.28wt%Pt-$TiO_2$/$Al_2O_3$ 촉매이었고, 고온에서는 1.1wt%Pt-$TiO_2$/$Mn_2O_3$(21) 촉매가 제일 높은 활성을 보였다. 그러나 수분 및 아황산가스 공존시와 열적 내구성 면에서는 0.55wt%Pt-$TiO_2$/5wt% Cu-ZSM-5 촉매가 가장 우수하게 나타났다.

• 한국재료학회지
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• 제32권11호
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• pp.496-507
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• 2022

For the selective catalytic reduction of NOx with ammonia (NH₃-SCR), a V₂O₅WO₃/TiO₂ (VW/nTi) catalyst was prepared using V₂O₅ and WO₃ on a nanodispersed TiO₂ (nTi) support by simple impregnation process. The nTi support was dispersed for 0~3 hrs under controlled bead-milling in ethanol. The average particle size (D₅₀) of nTi was reduced from 582 nm to 93 nm depending on the milling time. The NOx activity of these catalysts with maximum temperature shift was influenced by the dispersion of the TiO₂. For the V_0.5W₂/nTi-0h catalyst, prepared with 582 nm nTi-0h before milling, the decomposition temperature with over 94 % NOx conversion had a narrow temperature window, within the range of 365-391 ℃. Similarly, the V_0.5W₂/nTi-2h catalyst, prepared with 107 nm nTi-2h bead-milled for 2hrs, showed a broad temperature window in the range of 358~450 ℃. However, the V_0.5W₂/Ti catalyst (D₅₀ = 2.4 ㎛, aqueous, without milling) was observed at 325-385 ℃. Our results could pave the way for the production of effective NOx decomposition catalysts with a higher temperature range. This approach is also better at facilitating the dispersion on the support material. NH₃-TPD, H₂-TPR, FT-IR, and XPS were used to investigate the role of nTi in the DeNOx catalyst.

• 생물환경조절학회지
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• 제24권4호
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• pp.308-316
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• 2015

최근 관심이 집중되고 있는 스마트온실의 기술적용 실태와 문제점을 파악하고 이를 토대로 단동온실의 ICT 기술적용 장애요인 극복과 생산성을 제고하기 위하여 실험을 수행하였다. 자동화 시설의 도입 장애요인으로는 시설비 부담(24%)이 높았으며, 설치업체 사후관리 미흡(19%), 잦은 고장(16%), 관리기술 미흡(15%), 기능 미흡(13%), 소득향상기여 미흡(12%) 순이었다. ICT 도입필요성은 노동력절감(15%)이 가장 높았다. 자동화 온실에서 문제가 발생되는 부분은 온실구조, 구동기제어, 복합환경제어기, 센서기술이 각 14%로 비슷하였고, 원격제어기술 13%, 작물관리기술 12%, 에너지절감기술 10%, 소프트웨어활용 8%이었다. 온실구조 측면에서의 문제점은 천창개선이 18%로 가장 많았다. 효율적인 온도 및 환기 제어를 위해 농촌진흥청 고시 10-단동-7형 온실에 랙피니언 천창을 추가하였으며, 지붕형태를 복숭아형으로 변경하였다. 온실내 환경의 균일성을 위해 공기 유동팬은 6대를 설치하도록 하되 필요에 따라 증설 가능하도록 하였으며, 에너지 절약을 위해 1, 2중은 두께 0.1mm필름을 사용하고 3중은 5겹보온커튼을 설치하였다. CFD 유동해석 결과, 측창이 열린조건에서는 풍상 방향의 평균 유속이 빠르고 온도가 낮았으며, 풍하 방향으로 멀어 질수록 평균 유속이 점차 느려지고 온도는 높게 나타났다. 반면, 측창이 닫힌조건에서는 평균 유속이 낮으며, 구역별로 큰 편차는 없었다. 다만 풍상 풍하의 천창이 모두 열린 조건에 비하여 풍하 방향의 천창만 열린조건이 영역별 평균 유속에서 더 높은 값을 보였다. 측창을 닫은 조건에서는 외기의 유동이 아닌 온실 내 설치된 환기용 유동팬에 의해 유속이 발생하며 외부 환기가 없는 조건에서 유동팬에 의한 순환은 실내 전체 공간의 유동 편차를 줄여 줄 수는 있지만 전체적인 온도에는 영향을 미치지 못하였다. 저측고의 영역별 평균 온도는 고측고보다 균일하게 나타났다. 겨울철 3중 다겹보온커튼 여닫음에 관계없이 유동팬 근처에서 유속이 높고 유동팬에서 멀어지면 유속이 거의 없는 것으로 나타났다. 또한, 시간경과에 따른 평균 온도는 3중다겹보온커튼 열림상태에서 약 2시간 후에 외부온도와 같아졌으나 닫힘상태에서는 5시간 이후에 외부온도와 같아져, 3중 다겹보온커튼의 보온효과가 뚜렷하였다. 같은 조건에서 열용량의 차이로 인해 저측고 온실이 고측고 온실에 비하여 온도 하강 속도가 빨랐다.

• Tribology and Lubricants
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• 제27권2호
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• pp.71-76
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• 2011

In this study, the nondimensional load capacity of water hydrodynamic journal bearings is calculated. A generalized coordinate formulation is applied to handle the complexity of bearing geometry. A window-based analysis program is developed to analysis the cylindrical hydrostatic bearings. Load capacities are calculated according to some design parameters such as clearance, diameter of orifice, size of recesses and temperature. The results are presented and discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1238-1239
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• 2008

The high Tc supeconductor of ceramic oxides type was studied for finding its application field. The results reportaed in this paper on the stability of the ceramic superconductors and the resistance to ripening in the BCO liquid phase at elevated temperature opens a processing window for engineering the microstructure of large superconductor at the nanoscale level. The results suggest further that the introduction of highly efficient artifical pinning center to bulk ceramics superconductor.

• 산업경영시스템학회지
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• 제37권2호
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• pp.27-34
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• 2014

In this paper, we investigate the statistical correlation of the time series for temperature measured at the heat box in the automobile drying process. We show, in terms of the sample variance, that a significant non-linear correlation exists in the time series that consist of absolute temperature changes. To investigate further the non-linear correlation, we utilize the volatility, an important concept in the financial market, and induce volatility time series from absolute temperature changes. We analyze the time series of volatilities in terms of the de-trended fluctuation analysis (DFA), a method especially suitable for testing the long-range correlation of non-stationary data, from the correlation perspective. We uncover that the volatility exhibits a long-range correlation regardless of the window size. We also analyze the cross correlation between two (inlet and outlet) volatility time series to characterize any correlation between the two, and disclose the dependence of the correlation strength on the time lag. These results can contribute as important factors to the modeling of forecasting and management of the heat box's temperature.

• 한국태양에너지학회 논문집
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• 제32권4호
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• pp.51-58
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• 2012

This study aims to analyze characteristics of Cell surface temperature and generated power performance for improving PV(Photovoltaic) system condition according to the cell opening ratio of transparent crystal PV system at Spandrel of curtain-wall. For this purpose, alternatives were classified for eight different cases that opening ratio of transparent crystal PV system varied from 0% to 70%, which was used by simulation tool, EnergyPlus. As results, it turned out that increasing opening ratio of transparent crystal PV system led higher PV surface temperature, back-sheet type was thus the most advantageous for decreasing surface temperature, annual generating efficiency, and annual accumulated generating power. Consequently, blocking off air space from outside insolation can advantageously keep to be better condition for generated power performance.

• 한국군사과학기술학회지
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• 제17권1호
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• pp.8-14
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• 2014

Brightness temperature spectra acquired from FTIR(Fourier Transform Infrared)-SCADS (Standoff Chemical Agent Detection System) could be available for detection and identification of the chemical agents and pollutants from different background. IR spectrum range of 770 to 1350 $cm^{-1}$ is corresponding to "atmospheric window". A 2-dimensional(2D) brightness temperature spectrum was drawn from combining each data point through automatic continuous scanning of FTIR along with altitude and azimuth. At higher altitude, temperature of background was decreased but scattering effect of atmospheric gases was increased. Increase in temperature difference between background and blackbody in SCADS at higher temperature causes to increases in peak intensity of $SF_6$. This approach shows us a possibility that 2D visual information is acquired from scanning data with a single FTIR-SCADS.

• 한국환경과학회지
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• 제23권2호
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• pp.207-218
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• 2014

A ventilation model was developed for predicting the air change per hour(ACH) in buildings and the airflow rates between zones of a multi-room building. In this model, the important parameters used in the calculation of airflow are wind velocity, wind direction, terrain effect, shielding effect by surrounding buildings, the effect of the window type and insect screening, etc. Also, the resulting set of mass balance equations required for the process of calculation of airflow rates are solved using a Conte-De Boor method. When this model was applied to the building which had been tested by Chandra et al.(1983), the comparison of predicted results by this study with measured results by Chandra et al. indicated that their variations were within -10%~+12%. Also, this model was applied to a building with five zones. As a result, when the wind velocity and direction did not change, terrain characteristics influenced the largest and window types influenced the least on building ventilation among terrain characteristics, local shieldings, and window types. Except for easterly and westerly winds, the ACH increased depending on wind velocity. The wind direction had influence on the airflow rates and directions through openings in building. Thus, this model can be available for predicting the airflow rates within buildings, and the results of this study can be useful for the quantification of airflow that is essential to the research of indoor air quality(temperature, humidity, or contaminant concentration) as well as to the design of building with high energy efficiency.