• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.83-87
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• 1999

The fabrication process and thermal properties of 50~71vol% SiCp/Al metal matrix composites (MMCs) were investigated. The 50~71vol% SiCp/Al MMCs fabricated by pressure infiltration casting process showed that thermal conductivities were 118~170W/mK and coefficient of thermal expansion (CTE) were 9.5~$6.5{\times}10^{-6}/K$. Specially, the thermal conductivity and CTE of 71vol%SiCp/Al MMCs were 115~156W/mK and 6~$7{\times}10^{-6}/K$. respectively, which showed a improved themal properties than the conventional electronic packaging materials such as ceramics and metals.

• 대한기계학회논문집B
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• 제32권2호
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• pp.117-124
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• 2008

Recent researches on nanofluids have mainly focused on the increase of thermal conductivity of nanofluids under static condition. The ultimate goal of using nanofluids, however, is to enhance the heat transfer performance under fluid flow. So it has been highly necessary to devise a simple and accurate measuring apparatus which effectively compares the heat transfer capability between the base and nanofluids. Though the convective heat transfer coefficient is not the complete index for the heat transfer capability, it might be one of useful indications of heat transfer enhancement. In this article, the working principles of experimental system for convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids and its application example to three samples of nano lubrication oils are explained in detail.

• 한국세라믹학회지
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• 제24권3호
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• pp.277-281
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• 1987

The various contents of MgF2 from 0 to 12.5wt% are studied in the AlF3-(Mg＋Sr＋Ba)F2-P2O5 system for the effects of various properties in glasses and the atmosphere of melting was controlled by N2 and Ar gas respectively. Density, refractive index, infrared transmission, thermal conductivity and thermal expansion coefficient of glasses are determined. Density, refractive index and thermal conductivity are decreased, micro-hardness and thermal expansion coefficient are increased according to the increasing of MgF2 contents. Infrared transmittance decreases with increasing the MgF2 contents and it slightly dropped by air than N2 and Ar atmosphere. Other properties are not influenced by atmosphere control.

• 한국주조공학회지
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• 제13권4호
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• pp.342-349
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• 1993

The purpose of this study is to obtain basic information on the particle dispersion, the coefficient of thermal expansion and the thermal conductivity of compocasted Al-xSi-2Cu-1Mg/ySiC(x:6, 12, 18. $y:0{\sim}10wt.%$) composite. With increasing the content of SiC particles, the thermal expension coefficient and the thermal conductivity decrease. The coefficient of thermal expension between 20 and $300^{\circ}C$ is $21.3{\times}10^{-6}/^{\circ}C{\sim}18.0{\times}10^{-6}/^{\circ}C$ for the Al-Si alloys and $18.4{\times}10^{-6}/^{\circ}C{\sim}16.0{\times}10^{-6}/^{\circ}C$ for the composite with 10wt.% SiC. The thermal conductivity at $300^{\circ}C$ is $121{\sim}169W{\cdot}m^{-1}{\cdot}k^{-1}$ for the Al-Si alloys and $114{\sim}159W{\cdot}m^{-1}{\cdot}k^{-1}$ for the composite with 10wt.% SiC.

• 대한기계학회논문집B
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• 제38권4호
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• pp.347-355
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• 2014

전자장치들의 소형화 및 박형화가 됨에 따라 전자장치의 수명과 직결되는 열적문제가 중요해지고 있다. 열적문제를 해결하기위해 열확산과 단열을 통한 열적 안정성 연구가 필요하다. 허니컴 샌드위치 평판은 이방성의 열전도계수를 갖는다. 허니컴 샌드위치 평판이 적용된 시스템에 대해 온도분포와 열변형을 해석하기 위하여 열 및 탄성 물성치가 필요하다. 본 연구에서는 허니컴 코어의 크기, 두께 그리고 구성된 재료에 따라 허니컴 샌드위치 평판의 물성치가 변하기 때문에 허니컴 샌드위치 평판의 열전도계수, 열팽창계수, 탄성계수, 전단탄성계수, 푸아송비와 같은 열 및 탄성 물성치를 예측하였다.

• Tribology and Lubricants
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• 제30권1호
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• pp.29-35
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• 2014

The temperature-dependent tribological properties of brake discs for a train were examined in this study. The discs were produced using heat-resistant alloy steel, which showed different thermal conductivity after the heat treatments. A commercial brake friction material was used to evaluate the friction effectiveness, and the friction tests were carried out using a 1/5 scale dynamometer under various initial braking temperature conditions. The results showed that the tribological property of the disc was strongly affected by the heat treatment schedule. At low temperatures (below $250^{\circ}C$), the friction coefficient increased as a function of disc temperature, indicating that frictional heat increased the adhesion between the disc and pad. In addition, fade was observed at high temperatures (above $250^{\circ}C$); it was pronounced in the case of the disc with low thermal conductivity. The different fade resistances observed in the discs with different heat treatment schedules appear to be influenced by microstructural changes such as carbide redistribution occurring during the heat treatments, which affected the thermal conductivity.

• Bulletin of the Korean Chemical Society
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• 제31권11호
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• pp.3225-3227
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• 2010

The thermal conductivity of layered metal chalcogenides such as $MT_2$ (M = Mo, W; T = S, Se) shows a marked decrease after exfoliation and subsequent restacking process. Random stacking of two-dimensional crystalline sheets circumvents thermal conduction pathways along a longitudinal direction, which results in a reduction in thermal conductivity. $WS_2$ and $WSe_2$ compounds retain p-type conducting behavior after exfoliation and restacking with decreased electrical conductivity due to the change in carrier concentration. $MoSe_2$ compound exhibits metallic behavior < $130^{\circ}C$ with a small Seebeck coefficient, which results from metastable 1T-$MoSe_2$ structure of the restacked phase.

• Journal of Ceramic Processing Research
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• 제20권6호
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• pp.582-588
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• 2019

FeVSb1-xTex (0.02 ≤ x ≤ 0.10) half-Heusler alloys were fabricated by mechanical alloying process and subsequent vacuum hot pressing. Near single half-Heusler phases are formed in vacuum hot pressed samples but a second phase of FeSb2 couldn't be avoided. After doping, the lattice thermal conductivity in the system was shown to decrease with increasing Te concentration and with increasing temperature. The lowest thermal conductivity was achieved for FeVSb0.94Te0.06 sample at about 657 K. This considerable reduction of thermal conductivities is attributed to the increased phonon scattering enhanced by defect structure, which is formed by doping of Te at Sb site. The phonon scattering might also increase at grain boundaries due to the formation of fine grain structure. The Seebeck coefficient increased considerably as well, consequently optimizing the thermoelectric figure of merit to a peak value of ~0.24 for FeVSb0.94Te0.06. Thermoelectric properties of various Te concentrations were investigated in the temperature range of around 300~973 K.

• 설비공학논문집
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• 제11권2호
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• pp.185-192
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• 1999

Effective thermal conductivities and pressure-drop-related properties of aluminum foam metals have been measured. The effects of porosity and cell size in the aluminum foam metal are investigated in detail. The porosity of the foam metal, considered in the present study, varies from 0.89 to 0.96 and the cell size from 0.65㎜ to 2.5㎜. The effective thermal conductivity is evaluated by comparing the temperature gradient of the foam metal with that of the thermal conductivity-known material. The pressure drop in the foam metal is measured by a highly precise electric manometer while air is flowing through the aluminum foam metal in the channel. The results obtained indicate that the effective thermal conductivities are found to be increased with a decrease in the porosity while the effective thermal conductivities ire little affected by the cell size at a fixed porosity. However, the pressure drop is strongly affected by the cell size as well as the porosity. It is seen that the pressure drop is increased as the cell size becomes smaller, as expected. The minimum pressure drop is obtained in the porosity 0.94 at a fixed cell size. A new correlation of the pressure drop is proposed based on the permeability and Ergun's coefficient for the aluminum foam metal.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.603-610
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• 2021

The major drawback of zirconia-based materials, in view of their applications as targets for minor actinide transmutation, is their poor thermal conductivity. The addition of MgO, which has high thermal conductivity, to zirconia-based materials is expected to improve their thermal conductivity. On these grounds, the present study aims at phase characterization and thermophysical property evaluation of neodymium-substituted zirconia (Zr_0.8Nd_0.2O_1.9; using Nd₂O₃ as a surrogate for Am₂O₃) and its composites with MgO. The composite was prepared by a solid-state reaction of Zr_0.8Nd_0.2O_1.9 (synthesized by gel combustion) and commercial MgO powders at 1773 K. Phase characterization was carried out by X-ray diffraction and the microstructural investigation was performed using a scanning electron microscope equipped with energy dispersive spectroscopy. The linear thermal expansion coefficient of Zr_0.8Nd_0.2O_1.9 increases upon composite formation with MgO, which is attributed to a higher thermal expansivity of MgO. Similarly, specific heat also increases with the addition of MgO to Zr_0.8Nd_0.2O_1.9. Thermal conductivity was calculated from measured thermal diffusivity, temperature-dependent density and specific heat values. Thermal conductivity of Zr_0.8Nd_0.2O_1.9-MgO (50 wt%) composite is more than that of typical UO₂ fuel, supporting the potential of Zr_0.8Nd_0.2O_1.9-MgO composites as target materials for minor actinides transmutation.