• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.5
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• pp.233-239
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• 2013

The Thermophysical properties of thermal conductivity, viscosity, and heat capacity for $CO_2$ slurry ($CO_2$ gas and $CO_2$-hydrate mixture) having a high gas phase volume fraction were predicted using the conventional mixture models and the TRAPP model under hydrate formation conditions. Based on the calculated thermophysical properties, the heat transfer coefficient and pressure drop of the $CO_2$ slurry in the tube were predicted. The thermal conductivity of $CO_2$ slurry ranged from 0.02 to 0.2 W/m-K, and the mixture viscosity was larger than that of pure $CO_2$ by 1.9~2.7 times. The heat capacity of $CO_2$ slurry ranged from 63 to 68% of that for pure $CO_2$. The predicted heat transfer coefficient of $CO_2$ slurry was 6 times higher than that of pure $CO_2$. In the separate model, the estimated pressure drop increased with an increase of $CO_2$-hydrate mole fraction, and was 60% of that of pure $CO_2$.

• Journal of the Korean institute of surface engineering
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• v.32 no.2
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• pp.144-156
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• 1999

Thermal Barrier Coating with Functional Gradient Materials (FGM-TBC) can play an important role to protect the parts from harmful environments in high temperatures such as oxidation, corrosion, and wear and to improve the efficiency of aircraft engine by lowering the surface temperature on turbine blade. FGM-TBC can increase the life spans of product and improve the operating properties. Therfore, in this study the evaluations of mechanical and thermal properties of FGM-TBC such as fatigue, oxidation and wear-resistance at high temperatures have been conducted. The samples of both the TBC with 2, 3, 5 layers (YSZ/NiCrAlY) to be produced by Air Plasma Spray method (APS) and the bulk TBC with 6 layers to be produced by Plasma Assisted Sintering method (PAS) were used. Furthermore, residual stress, bond strength, and thermal conductivity were evaluated. The average thickness of the APS was 500$\mu\textrm{m}$ to 600$\mu\textrm{m}$ and the average thickness of the PAS was 3mm. The hardness number of the top layer of APS was 750 Hv to 810Hv and that of PAS was 950 Hv to 1440Hv. The $ZrO_2$ coating layer of APS was composed of tetragonal structure after spraying as the result of XRD analysis. As shown in the results of the high temperature wear test, the 3 layer coating of APS had the best wear resistance at $800^{\circ}C$ and the 5 layer coating of APS had the best wear resistance at $600^{\circ}C$. But, these coatings had the tendency of the low-temperature softening at $300^{\circ}C$. The main mechanism of wear was the adhesive wear and the friction coefficient of coatings was increased as increasing the test temperatures. A s results of thermal conductivity test, the ${\Delta}T$ of the APS coating was increased as number of layer and the range of thermal conductivity of the PAS was $800^{\circ}C$ to $1000^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.4
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• pp.41-48
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• 1999

Silica is the most popular materials as a filler of EMC for microelectronic packaging. However, because of its low thermal conductivity, the use of silica is restricted to parts requiring high thermal dissipation. The superior fluidity of EMC can be achieved with a combination of filler size distribution. In this study, physical properties of EMC filled with the crystalline silica(13$\mu\textrm{m}$) which have high fluidity and low cost and the AlN(2 $\mu\textrm{m}$) which have high thermal conductivity and low coefficient of thermal expansion were evaluated by changing the AlN/silica ratios. As a result of the evaluation of physical properties of EMC, the optimum mixing ratio of AlN/crystalline silica was 0.3/0.7. In this condition, binary mixture(AlN/crystalline silica) filled EMC showed superior properties, i.e., in the thermal conductivity, CTE, dielectric constant, flexural strength, and thermal shock resistance without reduction of fluidity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.603-608
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• 2023

Carbon black with high purity and excellent conductivity is used as a conductive filler in the semiconductive compound for EHV (Extra High Voltage) power cables of 345 kV or higher. When carbon black and CNT (carbon nanotube) are applied together as a conductive filler of a semiconductive compound, stable electrical properties of the semiconductive compound can be maintained even though the amount of conductive filler is significantly reduced. In EHV power cables, since the semi-conductive layer is close to the conductor, stable electrical characteristics are required even under high-temperature conditions caused by heat generated from the conductor. In this study, the theoretical principle that a semiconductive compound applied with carbon black and CNT can maintain excellent electrical properties even under high-temperature conditions was studied. Basically, the conductive fillers dispersed in the matrix form an electrical network. The base polymer and the matrix of the composite, expands by heat under high temperature conditions. Because of this, the electrical network connected by the conductive fillers is weakened. In particular, since the conductive filler has high thermal conductivity, the semiconductive compound causes more thermal expansion. Therefore, the effect of CNT as a conductive filler on the thermal conductivity, thermal expansion coefficient, and volume resistivity of the semiconductive compound was studied. From this result, thermal expansion and composition of the electrical network under high temperature conditions are explained.

• Coupled systems mechanics
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• v.12 no.2
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• pp.103-125
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• 2023

The present research is focused on the study of plane harmonic waves in a two-dimensional orthotropic magneto-thermoelastic media with fractional order theory of generalized thermoelasticity in the light of two-temperature and rotation due to time harmonic sources. Here, we studied three types of waves namely quasi-longitudinal (QL), quasi-transverse (QTS) and quasi thermal (QT) waves. The variations in the wave properties such as phase velocity, attenuation coefficient and specific loss have been noticed with respect to frequency for the reflected waves. Further the value of amplitude ratios, energy ratios and penetration depth are computed numerically with respect to angle of incidence. The numerical simulated results are presented graphically to show the effect of fractional parameter based on its conductivity (0<α<1 for weak, α=1 for normal, 1<α≤2 for strong conductivity) on all the components.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.3
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• pp.359-370
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• 2023

The thermal integrity of spent nuclear fuels has to be maintained during their long-term dry storage. The detailed temperature distributions of spent fuel assemblies are essential for evaluating the integrity of their dry storage systems. In this study, a subchannel analysis model was developed for a canister of a single fuel assembly using the COBRA-SFS code. The thermal parameters affecting the peak cladding temperature (PCT) of the spent fuel assembly were identified, and sensitivity analyses were performed based on these parameters. The subchannel analysis results indicated the presence of a recirculation flow, based on natural convection, between the fuel assembly and downcomer region. The sensitivity analysis of the thermal parameters indicated that the PCT was affected by the emissivity of the fuel cladding and basket, convective heat transfer coefficient, and thermal conductivity of the fluid. However, the effects of the wall friction factor of the canister, form loss coefficient of the grid spacers, and thermal conductivities of the solid materials, on the PCT were predominantly ignored.

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.1
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• pp.1-6
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• 2018

Subsea pipelines are designed to transport mixtures of oil, gas, and their associated impurities from the wellhead that can have temperatures as high as $100^{\circ}C$, while the external temperature can be as low as $5^{\circ}C$. Heat can be lost from the subsea pipeline containing high-temperature fluid to the surrounding environment. It is important that the pipeline is designed to ensure that the heat loss is small enough to maintain flow and avoid the unwanted deposition of hydrate and wax, which occurs at a critical temperature of approximately $40^{\circ}C$. Therefore, it is essential to know the heat loss of subsea pipelines under various circumstances. This paper presents a comparison between numerical analyses and existing theoretical formulas for different backfills and burial depth.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.49-52
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• 2004

New hydrophobic alumina nanoparticles were synthesized from alumina powders which were hydrophilic nano-agglomerates with diameters from ${\mu}m$ to mm by surface modification. The synthesized hydrophobic alumina nanoparticles which were retreated with Oleic acid were analyzed by Fourier transform infrared spectrophotometer and transmission electron microscopy. Then transformer oil containing surface-modified alumina naonparticles were synthesized. The synthesized hydrophobic alumina nanoparticles were well-dispersed in transformer oil. The coefficient of viscosity and dielectric strength of the Nano-transformer oil were investigated with viscometer and high voltage experiment device. In this study, the thermal conductivity of Nano-transformer oil was investigated to reduce the oil temperature of transformer by transient hot-wire method.

• Journal of Energy Engineering
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• v.24 no.2
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• pp.84-90
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• 2015

Hydrogen has some remarkably high values of the key properties for transport processes, such as kinematic viscosity, thermal conductivity and diffusion coefficient. Hydrogen, as an energy medium, has some distinct benefits for its high efficiency and convenience in storage, transportation and conversion. Hydrogen has much wider limits of flammability in air than methane, propane or gasoline and the minimum ignition energy is about an order of magnitude lower than for other combustibles. Statistical thermodynamics provides the relationships that we need in order to bridge this gap between the macro and the micro. Our most important application will involve the calculation of the thermodynamic properties of the ideal gas.

• Solar Energy
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• v.2 no.1
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• pp.1-8
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• 1982

A theoretical study by numerical method has been performed on the natural convection of an air contained in enclosures. The enclosures have rectangular cross section with one vertical wall heated and the other cooled, and with two horizontal partition plates of finite thermal conductivity. Steady two-dimensional flow was assumed. The computation was executed by means of the Implicit Alternating Direction (I.A.D) finite-difference method. Two partition plates of Aluminium whose thickness were 0.05mm was employed in computation. Isothemals, streamlines, local Nusselt numbers and mean Nusselt numbers were obtained for various Grashof numbers and aspect ratio and these results were compared with those in the case of the enclosure with two horizontal insulated plates. From the present results, the heat transfer in the case of partition plates was greater than that in the case of insulation. This study suggests a method to measure the overall heat-transfer of coefficient in double walls which supported by partition plates for insulative construction.