• Journal of ILASS-Korea
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• v.19 no.2
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• pp.82-87
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• 2014

Nanofluids are that metallic or nonmetallic nanometer-sized particles are dispersed in liquid. They can be used in various fields to increase the heat transfer rate because the thermal conductivity of nanofluids can be increased significantly. Nanofluids may be used as a good alternative of coolants in spray cooling. This study conducted experiments to compare the characteristics of sprays between water and nanofluid sprays. The radial distributions of droplet velocities and diameters of water, 0.2% wt.(weight), and 0.5% wt. $Al_2O_3$ nanofluids at the pressure of 0.2 and 0.3 MPa were measured by laser doppler instruments. The radial distributions of droplet diameters and velocities at two axial positions with water and 0.2% wt. nanofluid sprays didn't show much difference. A big difference, however, was observed between 0.5% wt. nanofluid and water sprays. With the increase of the mass of nano-particles, the average droplet diameters were increased and the average droplet velocities were decreased.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2439-2442
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• 2012

In order to explore the effects of the solvent on the formation rate of polyynes, we investigated the absorption spectra of polyynes obtained by laser ablation of a graphite target in different solvents at 1064 nm. Polyynes so produced were confirmed by the Raman band around $2200cm^{-1}$ which corresponds to the carbon triple bonds. The production of polyynes by laser ablation turned out to be significantly affected by the ratio of the hydrogen and carbon atoms in the solvent molecule. No clear correlations were observed in the formation of polyynes for other properties of the solvent such bond dissociation energy, thermal conductivity, and total mass of hydrogen atoms per volume of solvent.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.599-608
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• 2000

One dimensional numerical modeling was carried out for the melting behavior of dry snow and the unsaturated flow when heat was supplied from the bottom surface. Discrepancy between the previous experimental data and the present numerical results is substantially reduced by considering the density change of water permeation layer due to the infiltration of meltwater. In the parametric study for effective thermal conductivity, it was found that the effect of this parameter to the behavior of snow melting is minor. Sensitivity analysis showed that the melting time is most sensitive to changes in supplied heat flux, snow temperature, and bulk density, whereas snow bulk density and residual saturation have a significant effect on the height of water permeation layer in snow.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.861-864
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• 2006

This study investigates the properties of light weight foamed concrete with variances in incorporating ratio of cement kiln dust(CKD). Test showed that an increase of CKD incorporating ratio decreased the fluidity of fresh concrete and increased the unit weight. A sinking depth of specimens incorporating CKD decreased, compared with that of control. As for the compressive strength, it firstly increased and then slightly decreased when incorporated CKD. Tensile strength values were similar to the values of compressive strength, but the ratio of comp. to tens. strength increased. Appearances density of specimens were all raged in KS and the thermal conductivity was also satisfied in KS; less than 0.05-0.160W/($m{\cdot}k$).

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.765-768
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• 2006

This paper investigates the properties of light weight foamed concrete with variances in adding ratio of stability agent(PS). Test showed that an increase of PS adding ratio decreased fluidity due to higher viscosity and increased unit weight of specimens. A sinking depth declined as the adding ratio of PS inclines, but all specimens including control concrete was ranging in KS; 0.5 to 10mm. Compressive strength value of specimens increased as PS adding ratio inclines. As for the tensile strength, any significant feature was not observed, compared with control concrete, but the ratios of camp. to tens. increased. Appearance density of concrete increased, and thermal conductivity was satisfied in KS, except for a specimen adding 0.07 percent of PS.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.101-104
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• 1992

In-doped CdS thin films have been deposited at 150$^{\circ}C$ by simultaneous thermal evaporation of CdS and In. Deposition rate and film thickness were 8A/sec and about 1um, respectively. Indium doping concentration of films varied as Indium source temperature from 500$^{\circ}C$ to 700˚. Properties of In-CdS films have been investigatied by measurements of electrical resistivity, Hall effect, X-ray diffraction and optical trasmission spectra. The conductivity of these films was always n-type. The resistivity, carrier concentration, mobility and optical band gap dependence on Indium source temperature are reported. Carrier concentration and mobility of In-CdS films increased with increasing Indium source temperature: then they decreased. The variation of the optical band gap of In-CdS thin films are related to carrier concentration.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.344-348
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• 1999

Diamond like carbon(DLC) thin films possesed not only marvelous material characteristics such as large thermal conductivity, high hardness and being chemically inert, but also possesed negative electron affinity (NEA) properties. The NEA is an extremely desirable property of the material used in microelestronics and vacuum microelestronics device. DLC films were fabricated by pulsed laser deposition(PLD). Theeffect of the laser energy density and the substrate temperature on the properies of DLC films was investigated. The experiment was accomplished at temperatures in the range of room temperature to $600^{\circ}C$. The laser energy density was in the range of 6 $J/cm^2$ to 16 $J/cm^2$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.79-80
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• 2006

From a viewpoint of heat stress at high temperatures and contact thermal resistance, it is confirmed that the optimal structure is the skeleton structure using Cu substrate on the cooling side, which has excellent heat conductivity and the optimal installation method is to adopt a carbon sheet and a mica sheet to the high temperature side, where Si grease is applied to the low temperature side, under pressurized condition. The power of the developed modules indicated 0.5W in an $FeSi_2$ module and 3.8 W with a SiGe module at 823K, respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.430-431
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• 2006

Thermoelectric thick film was fabricated by screen printing process with using p-type Bi-Te-Sb powders. The powder was synthesized by melting, milling and sintering process and hydrogen reduced to enhance the thermoelectric property. The thick film of Bi-Te-Sb powder was fabricated by screen printing method and baked at the optimized conditions. The thermal conductivity, the electrical resistivity and Seeback coefficient of thick film were measured and the thermoelectric performance was analyzed in terms of film characteristics and its microstructure. Finally, the feasibility of thermoelectric thick film into micro cooling device on CPU chip was discussed in this study.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2015.11a
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• pp.138-140
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• 2015

건축물에서 단열재는 일정한 온도를 유지하도록 하려는 부분의 바깥쪽을 피복하여 외부로의 열손실이나 열의 유입을 적게 하기 위한 재료이다. 단열재는 소재(素材) 자체의 열전도율(熱傳導率)이 작은 것이 바람직하나, 대부분 열전도율이 그다지 작지 않다. 그러므로 대개의 경우 열전도율을 작게 하기 위해서 다공질(多孔質)이 되도록 만들어 기공(氣孔) 속의 공기의 단열성을 이용한다. 일반적으로 재료의 밀도가 크면 열전도율 값이 크게 되는 경향이 있다. 이에 본 연구에서는 경량골재인 펄라이트의 입자 크기별 열전도율을 측정하여 단열재로서 사용여부를 판단하고자 한다.