• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.221-224
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• 2014

We present a method for manufacturing a TIM used for packaging a high-power LED. In this method a mixture of diamond powder and hydrogen peroxide is used as a filler epoxy. The thermal resistance of the TIM with hydrogen peroxide was improved by about 30% over the thermal resistance of the TIM without hydrogen peroxide. We demonstrate that as a result the heat generated from the chip is easily dissipated through the TIM.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.34-41
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• 2001

A study has been conducted to observe the slot film cooling effect on a convergent nozzle wall. The slot film cooling is used to protect the nozzle wall from the hot combusted gas by the coolant injected from the slot around the inner wall of the nozzle. The film cooling effectiveness and the heat transfer to the nozzle wall are influenced significantly by the blowing ratio of the coolant to the main flow and those are also influenced by the shape of the slot and the flow acceleration in the nozzle. In the present study, the heat transfer for the various blowing ratios has been performed by the experimental method and the results are compared with the results computed by the empirical formula. The numerical method has been conducted to compare the film cooling effectiveness of the convergent nozzle with that of the cylinder. For the relatively low blowing ratio, the cooling effectiveness increases sharply as the blowing ratio increases, and the increasing rate slows down for the high blowing ratio.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1189-1196
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• 1988

Thermal entrance lengths of turbulent tube flow for viscoelastic polymer solutions are investigated experimentally in the recirculating flow system with tubes of inside diameters 8.5mm(L/D=710) and 10.3mm(L/D=1158), respectively. In the present system, the hydrodynamic and thermal boundary layers develop simultaneously from the beginning of the test section. To provide the boundary condition of constant heat flux at the wall, the test tubes are heated directly by electricity. The polymer solution used in the current study is 1000 wppm aqueous solution of polyacrylamide(Separan AP-273). The apparent viscosity of the polymer solutions circulating in the flow system are measured by the capillary tube viscometer at regular time intervals. Thermal entrance lengths vary due to the rate of degradation. The entrance lengths of degraded polymer solutions are about 500~600 times the diameter. However, the entrance lengths of fresh polymer solutions are greater than the lengths of the test tubes used in this study suggesting that thermal entrance lengths for viscoelastic polymer solutions are greater than 1100 tube times the diameters. Friction factor is almost insensitive to the degradation, but the heat transfer $j_{H}$-factor is affected seriously by degradation. Based on the present experimental data of fresh solutions a correlation for the heat transfer $j_{H}$-factor is presented.ted.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.625-632
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• 2021

In this paper, the applicability of bottom ash to insulation concrete was investigated to increase the utilization of bottom ash. Bottom ash was used as the aggregates in porous concrete and extensive experiments were conducted to investigate the characteristics of porous concrete using two types of bottom ash aggregates. The water-binder ratios of 0.25 and 0.35 were chosen and concrete specimens was produced with the compaction of 0.5, 1.5, and 3.0MPa to analyze the material properties at different compaction conditions. After concrete specimens were cured for 28 days at water tanks, unit weight, total void ratio, and thermal conductivity were measured. Based on the measured experimental results, the relationships between the unit weight, total void ratio, and thermal conductivity of porous concrete containing bottom ash was presented.

• Applied Chemistry for Engineering
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• v.22 no.3
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• pp.266-271
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• 2011

Single-walled carbon nanotube (SWCNT)/Epoxy composites were prepared for improving thermal conductivities and dispersion of SWCNTs in the epoxy matrix. Composites obtained different types of SWCNTs which are pristine and functionalized of the SWCNTs by acid and amine treatments. Three types of SWCNTs were dispersed in diglycidyl ether of bisphenol A (DGEBA) and bisphenol F (DGEBF). Enhanced interaction between functional groups on SWCNT and epoxy resins was evidenced by an improvement in the dispersion of the SWCNTs in the epoxy matrix. Thermal conductivity of composites containing acid SWCNTs were found to be much better than those containing pristine and amine treated SWCNTs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1466-1473
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• 2012

Soft icecream is made by scraping an ice formed on the inside of the cylindrical evaporator, where R-404A is evaporating in the annulus. The heat transfer characteristics of the refrigerant evaporation and those during icecream formation were experimentally investigated. Results show that the refrigerant-side heat transfer coefficients are highly dependent on the location in the evaporator due to the complex annulus configuration. The heat transfer coefficient at the inlet is generally lower than those of other locations. The average heat transfer coefficient increases as heat flux increases or saturation temperature decreases. A correlation is developed to predict the refrigerant-side heat transfer coefficient. The icecream-side heat transfer coefficient oscillates continuously due to the periodic removal of ice formed on the surface. The average heat transfer coefficient during icecream formation is approximately 280 W/$m^2K$, and that during single-phase cooling increased from 150 W/$m^2K$ to 250 W/$m^2K$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.923-930
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• 2012

The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.554-560
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• 2021

CRUD (chalk river unidentified deposits) is a porous material deposited on the surface of nuclear fuel during nuclear power plant operation. The CRUD is composed of metal oxides, such as iron, nickel, and chromium. It is essential to investigate the effects of the CRUD layer on the wall heat transfer between the nuclear fuel surface and the coolant in the event of a nuclear accident. CRUD only negatively affects the temperature of the nuclear fuel due to heat resistance because the effects of the CRUD layer on two-phase boiling heat transfer are not considered. In this study, the physical property models for the porous CRUD layer were developed and implemented into the SPACE code. The effects of boiling heat transfer models on the peak cladding temperature and quenching were investigated by simulating a reflood experiment. The calculation results showed some positive effects of the CRUD layer.

• 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 Crystal Growth and Crystal Technology
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• v.4 no.4
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• pp.363-369
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• 1994

Bimuth telluride base thermoelectrics are prepared by AC current applied hot pressing method. It is possible to minimize the defects arising from the vaporization of Te, thanks to the very short processing time compared to the single crystal growing method. The optimum conditions for the AC applied hot pressing of 95 mol% $Bi_2Te_3-5 mol% Bi_2Se_3$ thermoelectrics are sintering at $400^{\circ}C$, for 2 minutes, under 1500 kgf/$\textrm{cm}^2$, with the particle size of $125 to 250 {\mu}m$, range of powder. The resultant Z value (figure of merit) was $2.2{\times}10^{-3}/K$.