• 한국분무공학회지
• /
• 제19권4호
• /
• pp.174-181
• /
• 2014

This study investigates the effects of nanoparticle size and temperature on the thermal conductivity enhancement of water-based alumina ($Al_2O_3$) nanofluids, using the centrifuging method and relative centrifugal forces of differing magnitude to produce nanofluids of three different particles without involving any dispersants or surfactants. We determined the coupling dependency in thermal conductivity enhancement relative to nanoparticle size and temperature of the alumina nanofluids and also experimentally showed that the effect of temperature on thermal conductivity is strongly dependent on nanoparticle size. Also, our experimental data presented that the effective medium theory models such as the Maxwell model and Hasselman and Johnson model are not sufficient to explain the thermal conductivity of nanofluids since they cannot account for the temperature- and size-dependent nature of water-based alumina nanofluids.

• 호남수학학술지
• /
• 제38권3호
• /
• pp.435-454
• /
• 2016

This paper investigates the effect of dual-phase-lags on a thermoviscoelastic orthotropic solid with a cylindrical cavity. The cylindrical cavity is subjected to a thermal shock varying heat and its material is taken to be of Kelvin-Voigt type. The phase-lag thermoelastic model, Lord and Shulman's model and the coupled thermoelasticity model are employed to study the thermomechanical coupling, thermal and mechanical relaxation (viscous) effects. Numerical solutions for temperature, displacement and thermal stresses are obtained by using the method of Laplace transforms. Numerical results are plotted to illustrate the effect phase-lags, viscoelasticity, and the variability thermal conductivity parameter on the studied fields. The variations of all field quantities in the context of dual-phase-lags and coupled thermoelasticity models follow similar trends while the Lord and Shulman's model may be different. The influence of viscosity parameter and variability of thermal conductivity is very pronounced on temperature and thermal stresses of the thermoviscoelastic solids.

• 한국초전도ㆍ저온공학회논문지
• /
• 제15권1호
• /
• pp.6-10
• /
• 2013

We investigate the electrical and thermal transport properties of a sesquicarbide superconductor $La_2C_3$, including electrical resistivity, thermoelectric power, and thermal conductivity. The electrical resistivity exhibits a typical metallic character with a saturation behavior at high temperatures. The thermoelectric power shows a metallic behavior with pronounced phonon-drag effect, comparable with pure metals. The broad peak of the thermal conductivity is observed in the superconducting state, which is rapidly suppressed by magnetic fields. These observations suggest that the electron-phonon scattering is significant in $La_2C_3$, which is relevant with the relatively high-$T_c$ in $La_2C_3$ through strong electron-phonon coupling with low frequency phonon modes.

• 폴리머
• /
• 제34권2호
• /
• pp.108-115
• /
• 2010

본 연구는 MWCNT로 보강된 SBR 나노복합재료를 컴파운딩법(compounding)으로 제조하여 산 처리된 MWCNT와 커플링제 상호간의 물리적 화학적 특성을 조사하였다. 황산과 질산으로 산화된 MWCNT는 FT-IR 분석 결과 -COOH로 기능화됨을 확인하였고, Raman 분석 결과 표면의 defect 존재와 disorder됨을 확인하였다. 또한, 제조된 SBR 복합재료의 가황 특성, 전기적 열적 특성 및 기계적 특성을 비교 평가하였다. 그 결과 산 처리된 MWCNT와 커플링제와의 상호 결합력으로 인해 기계적 물성은 상대적으로 증가하였으나, 전기적 열적 특성은 MWCNT의 defects나 disorder의 형성과 chopping으로 인해 감소됨을 확인할 수 있었다.

• Carbon letters
• /
• 제16권1호
• /
• pp.34-40
• /
• 2015

In this study, in order to improve the thermal and electrical properties of epoxy/graphene nanoplatelets (GNPs), surface modifications of GNPs are conducted using silane coupling agents. Three silane coupling agents, i.e. 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (ETMOS), 3-glycidoxypropyltriethoxysilane (GPTS), and 3-glycidoxypropyltrimethoxysilane (GPTMS), were used. Among theses, GPTMS exhibits the best modification performance for fabricating GNP-incorporated epoxy composites. The effect of the silanization is evaluated using transmission electron microscopy (TEM), scanning electron microscopy, thermogravimetric analysis, and energy dispersive X-ray spectroscopy. The electrical and thermal conductivities are characterized. The epoxy/silanized GNPs exhibits higher thermal and electrical properties than the epoxy/raw GNPs due to the improved dispersion state of the GNPs in the epoxy matrix. The TEM microphotographs and Turbiscan data demonstrate that the silane molecules grafted onto the GNP surface improve the GNP dispersion in the epoxy.

• Design & Manufacturing
• /
• 제15권3호
• /
• pp.7-12
• /
• 2021

Plastic injection molds used for rapid heating and cooling must minimize surface damage due to friction and maintain excellent thermal and low electrical conductivity. Accordingly, various surface treatments are being applied. The properties of Al₂O₃ coating and DLC coating were compared to find the optimal surface treatment method. Al₂O₃ coating was deposited by thermal spray method. DLC films were deposited by sputtering process in room temperature and high temperature PECVD (Plasma enhanced chemical vapor deposition) process in 723 K temperature. For the evaluation of physical properties, the electrical and thermal conductivity including surface hardness, adhesion and wear resistance were analyzed. The electrical resistance of the all coated samples was showed insulation properties of 24 MΩ/sq or more. Especially, the friction coefficient of high temp. DLC coating was the lowest at 0.134.

• Nano
• /
• 제13권11호
• /
• pp.1850133.1-1850133.9
• /
• 2018

The hexagonal boron nitride nanosheets (BN) were firstly treated by silane coupling agents 3-aminopropyltriethoxysilane (KH550) and 3-glycidoxypropyl-trimethoxysilane (KH560) to introduce some amino and epoxy (EP) groups on the BN surface. These modified BN nanosheets were incorporated into an EP matrix to prepare BN@KH560/EP composites with excellent thermal conductivity and electrical insulation properties. Results showed that the thermal conductivity of BN@KH560/EP composite with 20 vol% BN dosage was found to be 0.442 W/($m{\cdot}K$), which was 81% higher than that of pure EP resin. Both BN/EP composites treated by KH550 and KH560 showed rather good electrical insulation properties, although the dielectric constant of BN@KH550/EP composites were slightly higher than BN@KH560/EP composites. Moreover, BN@KH560/EP composites also showed better thermal and mechanical properties than that of BN@KH550/EP composites.

• Macromolecular Research
• /
• 제14권5호
• /
• pp.517-523
• /
• 2006

The effects of particle content, size and shape on the thermal conductivity (k) and adhesion properties of thermally conductive, pressure-sensitive adhesives (PSAs) were investigated. The matrix resins were thermally crosslinkable, 2-ethylhexyl acrylic polyol and ultraviolet (UV)-curable, random copolymer consisting of acrylic oligomer and various acrylates. We found that k increased with increasing diameter and particle aspect ratio, and was further enhanced due to the reduction of the interfacial thermal barrier when the coupling agent, which increases the adhesion between particles and the matrix resin, was used. On the other hand, adhesion properties such as peel strength and tack of the thermally crosslinkable resin decreased sharply with increasing particle content. However, for UV curable resin, increased particle addition inhibited the decrease in adhesion properties.

• 한국지반공학회논문집
• /
• 제19권5호
• /
• pp.59-67
• /
• 2003

본 연구에서는 지하수 유동 특성 해석의 신뢰도 증진을 위해서 우리나라 심부결정질 암석의 접촉 면적과 간극의 변화양상, 구속압과 온도에 따라 유체투과율의 변화 양상을 살펴보고자 하였다. 또한 역학적 물성과 열적 물성을 측정하여 모델링의 입력자료에 대한 신빙성을 높일 수 있도록 하였다. 실험 결과 초기 평균 간극은 544.33$\mu\textrm{m}$∼898.62$\mu\textrm{m}$ 범위를 보였으며 분포특성은 로그-정규분포 형태를 보였다. 구속압 변화에 따라 유체투과율은 감소하는 경향이 나타나고 온도 증가에 따라 유체투과율이 감소하는 경향을 보였으며 접촉 면적이 커지면 유체투과율 변화 폭이 작아짐을 이론과 실험을 통해 규명하였다. 암석의 역학적, 열적 물성을 측정한 결과 기존에 측정된 우리나라 화강암의 물성치와 근사한 값을 가지는 것으로 나타났다.

• 한국정밀공학회지
• /
• 제27권1호
• /
• pp.91-98
• /
• 2010

The increasing of power and processing speed and miniaturization of central processor unit (CPU) used in electronics equipment requires better performing thermal management systems. A typical thermal management package consists of thermal interfaces, heat dissipaters, and external cooling systems. There have been a number of experimental techniques and procedures for estimating thermal conductivity of thin, compressible thermal interface material (TIM). The TIM performance is affected by many factors and thus TIM should be evaluated under specified application conditions. In compact packaging of electronic equipment the chip is interfaced with a thin heat spreader. As the package is made thinner, the coupling between heat flow through TIM and that in the heat spreader becomes stronger. Thus, a TIM characterization system for considering the heat spreader effect is proposed and demonstrated in detail in this paper. The TIM test apparatus developed based on ASTM D-5470 standard for thermal interface resistance measurement of high performance TIM, including the precise measurement of changes in in-situ materials thickness. Thermal impedances are measured and compared for different directions of heat dissipation. The measurement of the TIM under the practical conditions can thus be used as the thermal criteria for the TIM selection.