• Journal of the Korean institute of surface engineering
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• v.50 no.3
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• pp.198-205
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• 2017

Thermal dissipation was investigated for poly methyl methacrylate (PMMA) composite films containing graphite and multi wall carbon nanotube(CNT) powders as filler materials. After mixing PMMA with fillers, solvent, and dispersant, the pastes were prepared by passing through a three roll mill for three times. The prepared pastes were coated $15{\sim}40{\mu}m$ thick on a side of 0.4 mm thick aluminium alloy plate and dried for 30 min at $150^{\circ}C$ in an oven. The content of fillers in dried films was varied as 1, 2, and 5 weight % maintaining the ratio of graphite and CNT as 1:1. Raman spectra from three different samples exhibited D, G and 2D peaks, as commonly observed in graphite and multi wall CNT. Among those peaks, D peak was prominent, which manifested the presence of defects in carbon materials. Thermal emissivity values of three samples were measured as 0.916, 0.934, and 0.930 with increasing filler content, which were the highest ever reported for the similar composite films. The thermal conductivities of three films were measured as 0.461, 0.523, and $0.852W/m{\cdot}K$, respectively. After placing bare Al plate and film coated samples over an opening of a polystyrene box maintained for 1 h at $92^{\circ}C$, the temperatures inside and outside of the box were measured. Outside temperatures were lower by $5.4^{\circ}C$ in the case of film coated plates than the bare one, and inside temperatures of the former were lower by $3.6^{\circ}C$ than the latter. It can be interpreted that the PMMA composite film coated Al plates dissipate heat quicker than the bare Al plate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.29-36
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• 2015

Exact comparisons of the thermal conductivities of the base fluid and a nanofluid are very important in the early stages of nanofluid development. A simple procedure of measuring the thermal conductivity of the two fluids by the transient hot wire method and numerically dividing these values is used for this purpose. However, because the experiments are not performed simultaneously and the physical properties of the measurement system are sometimes not properly known, large errors are incurred during the evaluation process. This article proposes a new apparatus for thermal conductivity comparison where the working principle is mainly based on relative measurement rather than absolute measurement. The measuring circuit and data processing steps are explained in detail; a validation test was performed using the well-known glycerine and engine oil.

• Journal of the Korean Wood Science and Technology
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• v.45 no.3
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• pp.360-367
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• 2017

This study was carried out to compare the characteristics of low density fiberboards (LDFs) manufactured with different adhesive types such as melamine urea formaldehyde (MUF), phenol formalehyde (PF), emulsified MDI (eMDI) and latexes resins. As results, hard LDFs were successfully manufactured by MUF, PF and eMDI resins. Thermal conductivities of all LDFs were significantly lower than commercial medium density fiberboard. Especially, all LDFs showed comparable thermal insulation performance with extruded polystyrene foam (XPS). LDF manufactured with eMDI resins showed the highest physical properties such as thickness/length swelling by water absorption and bending strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.6
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• pp.2846-2851
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• 2012

Effects of ground tire rubber(GTR) and unexpanded $Expancel^{(R)}$ powders on the thermal conducting characteristics of rigid polyurethane foams(PUFs) were studied. Sub-micron sized GTR powders and $Expancel^{(R)}$ powders were used as the foam nucleating agents to improve the thermal insulating properties of the rigid PUFs. As the results, while the thermal conductivities of the GTR filled-PUF samples were increased linearly with GTR contents, those of $Expancel^{(R)}$ filled-PUF samples were decreased a little bit. It was considered from the results that GTR powders might predominantly play a role as the extending fillers. On the other hand, $Expancel^{(R)}$ powders could act as the foam nucleating agents based on the polar surface, showing smaller cell sized PUF with improved insulating characteristics.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.404-408
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• 1999

Effects of heating time and radiation under high temperature on the properties of thermal, mechanical and shielding ability of modified (KNS-101), hydrogenated bisphenol-A(KNS-201) type epoxy resin and phenol-novolac(KNS-301) type epoxy resin based neutron shielding materials that are used for shipping casks for radioactive material have been investigated. At early stages, the offset temperatures of KNS-101, KNS-201 and KNS-301 increased with the heating time under high temperature, but it was rarely affected by the heating time in the later stages. In addition, the thermal conductivities of KNS-101 and KNS-201 decreased with heating time, but that of KNS-301 increased with the heating time. On the contrary, the thermal expansion coefficients of neutron shielding materials decreased with heating time. At the high temperature, the tensile strength and flexural strength of the shielding materials decreased with heating time. On the contrary, the thermal expansion coefficients of neutron shielding materials decreased with heating time. At the high temperature, the tensile strength and flexural strength of the shielding materials of KNS-101 and KNS-301 increased with heating time, but those of KNS-201 decreased with heating time. The shielding ability of neutron shielding materials slightly increased with the radiation dose, and shielding abilities of shielding materials of KNS-101 and KNS-201 were affected to a more extent than that of KNS-301 by radiation dose under high temperature.

• Design & Manufacturing
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• v.10 no.3
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• pp.14-19
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• 2016

Thermally or electrically conductive filler reinforced polymer composites are extensively being developed as the demand for light weight material increases rapidly in industiral applications need good conductivity such as heat sink of the electronics or light. Carbon or ceramic materials like graphite, carbon nanotube or boron nitride are typical conductive fillers with good thermal or electical conductivity. Using these conductive fillers, the polymer composites in the market show wide range of thermal conductivity from approximately 1 W/mK to 20 W/mK, which is quite enhanced considering the thermal conductivity lower than 0.5 W/mK for most polymeric materials. The practical use of these composites, however, is yet limited to specific applications because most composites are still not conductive enough or too difficult to process, too brittle, too expensive for higher conductivity. For practical use of conductive composite, the thermal conductivity required depending on the heat releasing mode are studied first for simplified unit cooling geometry to propose thermal conductivities of the composites for reasonable cooling performance comparing with the metal heat sink as a reference. Also, as a practical design for heat sink based on polymer composite, composite and metal sheet hybrid structures are investigated for LED lamp heat sink and audio amplication module housing to find that this hybrid structure can be a good solution considering all of the cooling performance, manufacturing, mechanical performance, cost and weight.

• 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.

• Journal of Astronomy and Space Sciences
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• v.13 no.2
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• pp.105-116
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• 1996

This study is based upon the thermal modeling, analysis and operational results of KITSAT-1 and KITSAT-2 microsatellites launched on August 11, 1992 and Septermber 26, 1993, respectively. As KITSAT-1/2 was designed to be launched as an auxiliary payload of ARIANE launcher, the constraints on volume, power consumption, and mass were required to adopt passive thermal control method controlling absorptivity, emissivity, and conductivities among adjacent modules. The main of KITSAT was to take Earth images using CCD cameras positioned at the bottom of spacecraft, in which the cameras were always pointing to the center of Earth. This study is concerned with orbital analysis, thermal modeling, simulation results, and its verification by utilizing in-orbit telemetry data of KITSAT-2. The results of telemetry analysis show that the thermal modeling is matched to actual temperature data within 10 degrees of error range in average.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.1
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• pp.43-49
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• 2020

An engineered barrier system (EBS) for the geological disposal of high-level radioactive waste (HLW) consists of a disposal canister packed with spent fuel, buffer material, backfill material, and gap-filling material. The buffer material fills the space between the canister and the near-field rock, thus serving to restrain the release of radionuclides and protect the canister from groundwater penetration. Furthermore, as significant amounts of heat energy are released from the canister to the surrounding rock, the thermal conductivity of the buffer plays an important role in maintaining the safety of the entire disposal system. Therefore, given the high levels of heat released from disposal canisters, this study measured the thermal conductivities of compacted bentonite buffers from Gyeongju under temperature variations ranging 25 to 80~90℃. There was a 5~20% increase in thermal conductivity as the temperature increased, and the temperature effect increased as the degree of saturation increased.

• Polymer(Korea)
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• v.28 no.6
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• pp.455-459
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• 2004

Ionic conductivities of poly(ethylene oxide) (PEO)-based electrolytes are in a considerable inconsistency in many papers, varying more than three orders of magnitude for just same compositions. In PEO-salt-ceramic composite electrolytes, it has been also reported that the conductivity can be variant by almost three orders of magnitude according to thermal treatment and it has been regarded as a consequence of polymer-ceramic particle interaction. In this paper, we present a more systematic study on the change of ionic conductivity for ceramic-free PEO$_{10}$LiClO$_4$ polymer electrolytes, and found that the ionic conductivity can be variant more than hundred times according to thermal history. The slow recrystallization kinetics of PEO polymer is discussed to be responsible for the thermal history effect. Present results reveal that the effect of ceramic filler is not a main cause of the conductivity relaxation phenomenon.n.