• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.497-509
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• 1996

Evacuated powder insulations have long been known to have better thermal performance than existing commercially available insulators, such as fiber glass and CFC-blown foam. To make a composite powder panel, a series of individually evacuated panels was encapsulated in a rigid closed cell foam matrix. The panels were encapsulated in a thin glass sheet barrier to preserve the vacuum. The thermal conductivity of the individual panel was found to be $0.0062W/m^{\circ}K$ by experiment and the polyurethane foam above had a thermal conductivity of $0.024W/m^{\circ}K$. In this study, numerical analysis using finite element method was carried out to investigate insulation performance of rigid foam/evacuated powder composite panel with respect to panel geometries such as panel pitch, panel aspect ratio and panel area ratio. Numerical analysis has indicated that more optimal vacuum panel geometries, much lower overall thermal conductivities can be achieved.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2618-2623
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• 2013

A hybrid model is proposed to easily predict the effective thermal conductivity of composites with aligned- and coated-short fibers, whose aspect ratio is not constant. The thermal conductivities of coated fillers are computed by using the generalized self-consistent model, resulting in that composites are simply simulated by the matrix with the equivalent short fibers. Finally, the thermal conductivity of the composites is predicted using the modified Eshelby model. The predicted results by the representative models and hybrid model are compared for the composite with aligned- and coated-short fibers of single aspect ratio. It is demonstrated that the hybrid model can be applied to the composite with aligned- and short-fibers of aspect ratios, 2 and 10, without any difficulties.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.533-544
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• 2008

To obtain the physical properties of grout materials, that is the thermal conductivity and viscosity, which are used for backfilling ground heat exchangers, nine bentonite grouts and cement grouts being adapted in the United State have been considered in this study. The bentonite grouts show that the thermal conductivity and viscosity increase with the content of bentonite or filler (silica sand). The saturated cement grouts appear to possess much higher thermal conductivity than the saturated bentonite grouts, and the reduction of thermal conductivity in the cement grouts after drying specimens is less than the case of the bentonite grouts. To investigate the performance of cement grouts, fifteen samples were prepared by varying the water/cement ratio and the amount of sand and bentonite added into the cement mortar. Maintaining the moisture content of grouts is a crucial factor in enhancing the efficiency of ground heat exchangers.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.5
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• pp.293-298
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• 2004

For the application of heat sink device, the green sheets of powder of W-XCu and Mo-XCu composites were fabricated by tape casting technique. The mixing ratio of powder and binder was 6:4. The green sheet was shrinked up to 10~20% after sintering and the maximum relative density was above 95%. Thermal conductivity and Thermal expansion systematically increased with increasing Cu contents. The maximum thermal conductivity of W-20wt.%Cu was about 206[W/mK].

• Journal of Powder Materials
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• v.17 no.4
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• pp.342-346
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• 2010

In the present work, water-based gold nanofluids were synthesized by the solution plasma processing (SPP). The size distribution and the shape of gold nanoparticles in the nanofluids were investigated using high resolution transmission electron microscopy (HR-TEM). The dispersion stability of gold nanofluids was characterized using zeta potential, as well. The thermal properties of gold nanofluids were measured by utilizing lambda measurement device. Nanofluids containing nanoparticles with $64.0{\pm}42.1\;nm{\sim}18.10{\pm}5.0\;nm$ in diameter were successfully synthesized. As diameter of nanoparticles decreased, dispersion stability of nanofluids increased and the enhanced ratio of thermal conductivity increased. The nanofluid with nanoparticles of $18.10\;{\pm}\;5.0\;nm$ in diameter showed approximately 3% improvement in thermal conductivity measurement and this could be due to the enhanced Brownian movement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.182-188
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• 2018

Recently, various researches on the utilization of carbon nanotube(CNT) with superior electrical conductivity and large surface areas into concrete have been actively conducted. Thus, mechanical and thermal properties of cement-flyash composites were evaluated concerning the CNT replacements. Based on the low binder-to-water ratio, the cement composites were produced with 0.2 % and 0.5 % of CNT solids. The compressive strengths with various ages, isothermal calorimetry measurement, SEM analysis, thermal conductivity of cement composites and thermal gravimetry analysis were implemented. As the amount of CNT addition was increased, the thermal conductivity of cement composites were also increased. Also, there was no significant mechanical property differences between mixtures with and without CNTs.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.919-924
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• 2001

The purpose of this study is to prepare the basic data for the development of building board with expanded perlite. Each paste was mixed with four levels of water cement ratio(30, 40, 50, 60%), and expanded perlite was substituted with four levels of substitutive ratio(20, 40, 60, 80%) for the each paste. The physical property, compressive strength, bending strength and thermal conductivity of each cement composite which is made through previously described method were analyzed and the result was as follow. In the case of 80 percent substitutive ratio, the cement composite had a mechanical defect which was resulted from lack of paste content. In the case of 40 and 60percent substitutive ratio, the cement composite had sufficient strength, light weight and low thermal conductivity for application to fire resisting board.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.12 no.1
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• pp.94-102
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• 1999

Ni/CGO cermets were fabricated as the anode for SOFC which uses CGO as the electrolyte. And their electrical conductivity, electrochemical reactivity, and thermal expansion coefficient were optimized through the variation of NiO/CGO particle size ration and their composition. The electrical conductivity of the cermet was increased abruptly at a certain Ni content and the percolation concentration was decreased with the decreasing particle size ratio. Anodic overpotential was also decreased with the decreasing particle size ratio. For a fixed ratio it showed a minimum value at 50 wt.%. Thermal expansion coefficient was increased monotonically with increasing Ni contents, however it did not depend on the size ratio. With three properties taken into account, the cermet of particle size ration of 0.03 and composition of 50 wt.% was judged to be optimal as the anode.

• Composites Research
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• v.34 no.1
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• pp.63-69
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• 2021

In order to develop an integrated heat dissipating material and gas barrier film for electronics, new polymer was designed and synthesized for preparing composites containing hexagonal boron nitride (hBN) filler. Depending on the size and content of the hBN filler, both thermal conductivity and oxygen transmission rate can be adjusted. The composite achieved a high thermal conductivity of 28.0 W·m-1·K-1 at most and the oxygen transmission rate was decreased by 62% compared to that of the filler free matrix. Effective filler aspect ratios could be estimated by comparing thermal conductivity and oxygen transmission rate with values predicted by theoretical models. Discrepancy on the aspect ratios extracted from thermal conductivity and oxygen transmission rate comparisons was also discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.2
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• pp.73-81
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• 2019

Numerical simulations are performed for the thermal fluid flow around a circular cylinder, and the particle trajectories are calculated to investigate the particle motions and deposition characteristics. We aim to understand the effects of three important parameters (particle Stokes number, temperature difference in the flow and on the cylinder surface, and thermal conductivity ratio between the fluid and the particles) on the deposition efficiency. The results show that the thermophorectic effect is insignificant for particles with large Stokes numbers, but it affects particles with small Stokes numbers. The deposition efficiency increases with the increase in temperature difference between the flow and the cylinder or the decrease in ratio of thermal conductivity of the particles to the fluid. When thermophoresis becomes significant, the particles are deposited even on the back side of the cylinder.