• KIEAE Journal
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• v.7 no.6
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• pp.17-22
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• 2007

The integration of PV modules into building facades or roof could raise their temperature that results in the reduction of PV system's electrical power generation. Hot air can be extracted from the space between PV modules and building envelope, and used for heating in buildings. The extraction of hot air from the space will enhance the performance of BIPV systems. The solar collector utilizing these two aspects is called PV/T(photovoltaic/thermal) solar collector. This paper compares the experimental performance of two different types of air type PV/T collector units: the base case of a collector unit with 10cm gap for forced ventilation and the other unit with copper pin attached to PV module to enhance its thermal performance. The experimental results shows that the base case unit had the overall efficiency of 41.9% and the improved unit with copper pin attached to PV module had 50.1% efficiency. For these air type PV/T units, the forced ventilation of the air space improved the electrical performance as well as the thermal performance.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.366-366
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• 2022

유역의 하천유량과 같은 수문 시계열을 모의 또는 예측하기 위한 수문 모델링에서 최근 기계 학습 방법을 활용한 연구가 활발하게 적용되고 있는 추세이다. 이러한 데이터 기반 모델링 접근법은 입출력 자료에서 관찰된 패턴을 학습하며, 특히, 장단기기억(Long Short-Term Memory, LSTM) 네트워크는 많은 연구에서 수문 시계열 예측에 대한 적용성이 검증되었으나, 장기간의 고품질 관측자료를 활용할 때 더 나은 예측성능을 보인다. 그러나 우리나라의 경우 장기간 관측된 고품질의 하천유량 자료를 확보하기 어려운 실정이다. 따라서 본 연구에서는 LSTM 네트워크의 학습 시 가용한 모든 유역의 자료를 통합하여 학습시켰을 때 하천유량 예측성능을 개선할 수 있는지 판단해보고자 하였다. 이를 위해, 우리나라 13개 댐 유역을 대상으로 대상 유역의 자료만을 학습한 모델의 예측성능과 모든 유역의 자료를 학습한 모델의 예측성능을 비교해 보았다. 학습은 2001년부터 2010년까지 기상자료(강우, 최저·최고·평균기온, 상대습도, 이슬점, 풍속, 잠재증발산)를 이용하였으며, 2011년부터 2020년에 대해 테스트 되었다. 다지점 통합학습을 통해 테스트 기간에 대해 예측된 각 유역의 일 하천유량의 KGE 중앙값이 0.74로 단일지점 학습을 통해 예측된 KGE(0.72)보다 다소 개선된 결과를 보여주었다. 다지점 통합학습이 하천유량 예측에 큰 개선을 달성하지는 못하였으며, 추가적인 가용 자료 확보와 LSTM 구성의 개선을 통해 추가적인 연구가 필요할 것으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.1
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• pp.9-15
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• 2011

In this study, we investigated the hydrodynamic and thermal performance of constructal architectures on the basis of the mass flow rates for a given pressure drop, and we determined the thermal resistance and flow uniformity. The five flow configuration used in this study were the first construct with optimized hydraulic diameter, the second construct with optimized hydraulic diameter, the first construct with non-optimized hydraulic diameter, second construct with non-optimized hydraulic diameter, and a serpentine configuration. The results of our study suggest that the best fluid-flow structure is the second constructal structure with optimized constructal configurations. We also found that in the case of the optimized structure of cooling plates, the heat transfer was remarkably higher and the pumping power was significantly lower than those of traditional channels.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.2
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• pp.191-196
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• 2014

The solar water heating system is one of the seven green campus items installed at the Gangneung campus of Gangneung-Wonju National University. The solar water heating system has two types of solar collectors, four storage tanks and monitoring equipment. Fixed and azimuth-tracking solar collectors were installed to collect heat from the sun. The amount of heat collected by the two different types of solar collectors was calculated from the temperature of the monitored storage tanks. Our results showed that the amount of solar heat collected by the azimuth-tracking solar collector was 19% greater on a sunny day and 23% greater on a rainy day than that collected by the fixed solar collector; therefore, the azimuth-tracking solar collectors are, on an average, 21% more efficient than the fixed solar collectors.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.356-361
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• 2012

Recently, even though the researches on renewable energy like geothermal, wind, solar energy have been performed widely, its use-rate in total energy is still low. This study was carried out to investigate the performance of hybrid heating system, which consisted of solar collector of thermosyphon tube type and X-L pipe boiler. Especially, new type of solar collector was tried and compared with double tube type and, futhermore, performance and safety on X-L pipe boiler were investigated. As the results, efficiency of solar collector of thermosyphon tube type was higher 20.7% than that of double tube type, mainly due to its structural characteristics. It was also confirmed that temperature of special heat medium used X-L pipe boiler rose up about 20% rapidly in comparison with that of pure water.

• Journal of the Korea Convergence Society
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• v.13 no.3
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• pp.191-196
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• 2022

Unlike an international combustion engine car, a battery-powered electric vehicle requires an additional heat source for its heating system. A high-voltage coolant heater has the advantages of high efficiency and a wide operating temperature range. In its development, the geometry design of the coolant flow path is essential. This paper presents the thermal flow simulations of a 7kW high-voltage heater with symmetric serpentine flow channels arranged parallelly. The heater performance was evaluated from the simulation results in terms of the pressure and temperature differences and the flow uniformity. The proposed design showed a greater flow resistance and similar heat exchanging capability than the existing parallel serpentine design. It has the advantage of a relatively wide low-temperature surface area, where the control circuit board susceptible to high temperatures can be located.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.103.2-103.2
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• 2013

위성체는 우주공간의 고진공 상태와 태양 복사열에 의한 고온 및 극저온이 반복되는 가혹한 환경으로 인해 주요 부품의 기능장애가 초래되므로 발사전 지상에서 열진공 시험장비를 이용한 열진공시험을 수행한다. 우수한 성능의 위성체 부품의 검증을 위해서 열환경 시험 요구에 따라 균일한 복사열이 매우 중요하나, 시험 조건을 비롯하여 여러 원인으로 인하여 열전달의 불균일성이 발생하게 된다. 이로 인해 시스템에 큰 영향을 미칠 수 있으므로, 시험 조건에 의한 열전달량을 고려하여 적절한 히터파워를 선정하고 챔버 내에 적절한 방열판과 챔버 슈라우드의 열교환이 간섭이 없도록 장비를 운용해야 한다. 본 연구에서는 상용프로그램인 FLUENT를 이용하여 열진공 챔버 내부 벽면의 불균일한 복사열에 따른 비정상 열전달 특성에 대하여 수치해석을 수행한 뒤 시편의 온도 분포 및 열전달 특성에 대해 비교분석하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.61-64
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• 2014

문자열 매칭은 긴 텍스트 문자열 상에 짧은 질의 문자열이 나타나는 모든 위치를 찾는 문제이다. 텍스트 문자열이 고정되어 있는 경우에는 접미사 트리나 접미사 배열과 같은 자료구조를 이용하여 보다 효율적인 문자열 매칭을 수행할 수 있다. 이 때 사용자 인터페이스에 관련되어, 또는 다른 통계적 처리를 수행하기 위하여 주어진 질의 문자열의 출현 위치에 대한 히스토그램을 계산할 필요성이 있다. 그러나 질의 문자열의 출현 횟수가 많은 경우 각 출현 위치를 모두 순회하며 집계해야 하므로 시간적으로 매우 비효율적이다. 본 논문에서는 웨이블릿 트리를 이용하여 접미사 배열을 색인함으로써 히스토그램 계산에 있어서 질의 문자열의 출현 횟수와는 시간적으로 독립적인 집계 기법을 제안한다. 또한 실험을 통하여 질의 문자열의 출현 횟수가 많을수록 제안 기법의 성능이 우수함을 보인다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1222-1228
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• 2008

A small satellite, DubaiSat-1 FM(Flight Model), which is based on SI-200 standard bus platform and scheduled to be launched in 2008, is being developed by Satrec Initiative and EIAST(Emirates Institution for Advanced Science and Technology). The TCS(Thermal Control Subsystem) of DubaiSat-1 FM has been designed to mainly utilize passive thermal control in order to minimize power consumption, but the active control method using heaters has been applied to some critical parts. Also, thermal analysis has been performed for DubaiSat-1's mission orbit using a thermal analysis model. The thermal design is modified and optimized to satisfy the design temperature requirements for all parts according to the analysis result. The thermal control performance of DubaiSat-1 FM is verified by thermal vacuum space simulation, consisting of thermal cycling and thermal balance test. Also, to validate the thermal modeling of DubaiSat-1 FM, comparison of test results with analysis has been performed and model calibration has been completed.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.189-195
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• 2014

The use of solar energy among renewable energy tends to increase because of its infinity and cleanness of resources. Even though the consumption rate of solar energy in our country is still low, however, in recent years, the research for solar energy have been widely conducted due to policy support of government. This study was performed to investigate the efficiency of heat collection using solar collector with single evacuated tube-type. As the results, the temperature of radiation fin for solar collector with single evacuated tube-type was lower in spite of high temperature of heat pipe compared that of double evacuated tube-type. In order to increase the efficiency of heat collection, it was confirmed that the loss of heat collection due to contact resistance as well as performance improvement for solar collector should be decreased.