• Current Photovoltaic Research
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• v.6 no.2
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• pp.39-42
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• 2018

When the PV module is illuminated in a high temperature region, solar cells are also exposed to the high temperature external environment. The operating temperature of the solar cell inside the module is increased, which causes the power drops. Various efforts have been made to reduce the operating temperature and compensate the power of solar cells according to the outdoor temperature such as installing of a cooling system. Researches have been also reported to lower the operating temperature of solar cells by improving the heat dissipation properties of the backsheet. In this study, we conducted a test to measure the internal temperature of each module components and the external temperature when the light was irradiated according to the surrounding temperature. Backsheets with different thermal conductivities were compared in the test. Finally, in order to explain the temperature difference between the solar cell and the outside of the module, we proposed an evaluation method of the heat transfer characteristics of photovoltaic modules with different backsheet.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.77-86
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• 2002

위성은 일단 한 번 발사하고 나면 운용궤도상에서 수리 및 회수가 거의 불가능하기 때문에 위성에 들어가는 모든 개발 부품들은 완벽한 설계, 충분한 해석, 고 작업도의 제작, 그리고 다양한 시험이 반드시 수반되어야 한다. 위성시스템에서 전자 소자의 신뢰성에 영향을 주는 인자는 다양하다. 과도한 열은 전자소자의 실패를 유발해서 결과적으로는 전체 위성의 실패를 유도할 수 있다. 이 논문에서는 다목적 실용위성 2호의 고전력 소산 전장품의 열부하 완화를 위한 방안을 경우별로 연구 비교하였다. 고전력 소산 전장품의 열부하를 완화하기 위해서는 하우징 두께의 증가가 필요하며, 전력조절기의 다이오드나 트랜지스터처럼 전력소산이 큰 소자에 대해서는 장착위치를 변경하거나 장착 부분의 열전도율을 증가시키는 방법이 필요하다. 또한 전력조절기처럼 장착면이 좁은 경우에는 복사의 영향이 크며, 이러한 전장품의 열부하를 완화하기 위해서는 주위 벽면의 온도를 낮추거나 하우징 표면 방사율을 증가시키는 방법이 효과적임이 알 수 있다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.1058-1062
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• 2000

We investigated resistive superconducting fault current limites (SFCLs) fabricated using YBCO thin films on 2-inch diameter sapphire substrates. Nearly identical SFCL units were prepared and tested. The units were connected in series and parallel to increase the current and voltage ratings. A serial connection of the units showed significantly unbalanced power dissipation between the units. This imbalance was removed by introducing a shunt resistor to the firstly quenched unit. Parallel connection of the units increased the current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current 25 A$\_$peak/, was produced and successfully tested at a 220 V$\_$rms/circuit. From the resistance increase, we estimated that the film temperature increased to 200 K in 5 msec, and 300 K in 120 msec. Successive quenches revealed that this system is stable without degradation in the current limiting capability under such thermal shocks as quenches at 220 V$\_$rms/.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.265-274
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• 2007

A study has been conducted to clarify NO emission behavior through preferential diffusion effects of $H_2$ and H in methane-hydrogen diffusion flames. A comparison is made by employing three species diffusion models. Special concerns are focused on what is the deterministic role of the preferential diffusion effects in flame structure and NO emission. The behavior of maximum flame temperatures with three species diffusion models is not explained by scalar dissipation rate but the nature of chemical kinetics. The preferential diffusion of H into reaction zone suppresses the populations of the chain carrier radicals and then flame temperature while that of $H_2$ produces the increase of flame temperature. These preferential diffusion effects of $H_2$ and H are also discussed about NO emissions through the three species diffusion models.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.272-275
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• 2000

We investigated a resistive superconducting fault current limiter (SFCL) fabricated using YBCO thin films on 2-inch diameter sapphire substrates. Nearly identical SFCL units were prepared and tested. The units were connected in series and parallel to increase the current and voltage ratings. A serial connection of the units showed significantly unbalanced power dissipation between the units. This imbalance was removed by introducing a shunt resistor to the firstly quenched unit. Parallel connection of the units increased the current rating. An SFCL module of 4 units in parallel, each of which has minimum quench current 25 Ap, was produced and successfully tested at a 220 V circuit. From the resistance increase, we estimated that the film temperature increases to 200 K in 5 msec, and 300 K in 120 msec. Successive quenches revealed that this system is stable without degradation in the current limiting capability under such thermal shocks as quenches at 220 V.

• Fashion & Textile Research Journal
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• v.4 no.6
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• pp.564-566
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• 2002

Protective clothing for firefighters typically consists of a flame resistant outer shell and inner layers. The inner layers are generally composed of a moisture barrier and a thermal barrier. On performing the task in fire place the heat and perspiration generated from the body become trapped inside the protective clothing. Those heat and moisture result into heat-stress and physical fatigue of fire fighter, which hinder the work. Therefore, the system of clothing designs and material layers must be chosen carefully to balance protection and comfort. 3 kinds of protective clothing of 3 layer structure were used in the experiment of physiological comfort. From the comparison of wear trials with the 3 kinds of layers in firefighters clothing, it indicates that the moisture dissipation of A+B2+C was highest, following A+BI+C andA+B3+C. And the heat dissipation of A+BI+C and A+B2+C were better than A+B3+C. In the protective clothing with A+B3+C, heat and perspiration generated through exercise remained in clothing system long and caused discomfort.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1200-1205
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• 2014

The effect of nanofluids on the heat transfer performance of a pulsating heat pipe has been experimentally investigated. Water-based diamond nanofluid and aluminium oxide ($Al_2O_3$) nanofluid were tested in the concentration range of 0.5-5%. The pulsating heat pipe was constructed using clear Pyrex tubes of 1.85 mm in inner diameter in order to visualize the pulsating action. The total number of turns was eight each for heated and cooled parts. The supply temperatures of heating water and cooling water were fixed at $80^{\circ}C$ and $25^{\circ}C$ respectively. The liquid charging ratio of the nanofluid was 50-70%. The test results showed that the case of 5% concentration of diamond nanofluid showed 18% increase in heat transfer rate compared to pure water. The case of 0.5% concentration of $Al_2O_3$ nanofluid showed 24% increase in heat transfer rate compared to pure water. But the increase of $Al_2O_3$ nanofluid concentration up to 3% did not show further enhancement in heat transfer. It is also observed that the deposited nanoparticles on the tube wall played a major role in enhanced evaporation of working fluid and this could be the reason for the enhancement of heat transfer by a nanofluid, not the enhanced thermal conductivity of the nanofluid.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.621-628
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• 2019

The use of the ammonia-water zeotropic mixture as a working fluid in the power generating system has been considered as a proven technology for efficient recovery of low-grade heat sources. This paper presents a thermodynamic performance analysis for ammonia-water evaporator using low-grade heat source, based on the exergy and entransy which has been recently introduced as a physical quantity to describe the heat transfer ability of an object. In the analysis, effects of the ammonia mass fraction and source temperature of the binary mixture are investigated on the system performance such as heat transfer, effectiveness, exergy destruction, entransy dissipation, and entransy dissipation based thermal resistance. The results show that the ammonia mass concentration and the source temperature have significant effects on the thermodynamic system performance of the ammonia-water evaporator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.830-836
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• 2012

An efficient cooling system is essential for the electronic packaging such as a high-luminance LED lighting. A special heat transport technology, Pulsating Heat Pipe (PHP), can be applied to the cooling of LED lighting. In this paper, the operational characteristics of the PHP in the imposed thermal boundary conditions of LED lighting were experimentally investigated. The experimental PHP was made of copper tubes of internal diameter of 2.1 mm. The working fluids of ethanol, FC-72, water, acetone and R-123 were chosen for comparison. The results showed that an optimum range of charging ratio exists for high cooling performance; 50% for most of the fluids. Among the five working fluids, water showed the highest heat transfer rate of 260 W. Two distinguished characteristics of pulsating direction were identified. It is also identified that high vapor pressure gradient is one of key parameters for better heat transfer performance.

• Journal of Electrical Engineering and Technology
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• v.6 no.5
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• pp.671-676
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• 2011

A multilayer square-type piezoelectric transformer with a hole at the center was investigated in this paper. Temperature distribution at the center was improved by using this construction, therefore increasing input voltage and output power. This model was simulated and investigated successfully by applying a finite element method (FEM) in ATILA software. An optimized structure was then fabricated, examined, and compared to the simulation results. Electrical characteristics, including output voltage and output power, were measured at different load resistances. The temperature distribution was also monitored using an infrared camera. The piezoelectric transformer operated at first radial vibration mode and a frequency area of 70 kHz. The 16 W output power was achieved in a three-layer transformer with 96% efficiency and $20^{\circ}C$ temperature rise from room temperature under 115 V driving voltage, 100 ${\Omega}$ matching load, $28{\times}28{\times}1.8mm$ size, and 2 mm hole diameter. With these square-type multilayer piezoelectric transformers, the temperature was concentrated around the hole and lower than in piezoelectric transformers without a hole.