• Journal of Powder Materials
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• v.29 no.6
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.6
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• pp.413-418
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• 2010

The amount of heat loss of a refrigerator through the gasket is nearly 30% of total refrigerator heat loss. In this paper, quantitative evaluation for the effects of various effort to reduce heat losses through the gasket. The first trial is to extend the inner gasket to prevent the heat loss flowing from the inner of refrigerator. The effects of thermal conductivity changes of gasket and magnet are investigated by the numerical heat transfer analysis. The position change of hot line is also examined in the present research. From the present result of the numerical simulation of heat transfer, we are able to reduce the heat loss about 20~40% by using inner gasket extension. The reducing of thermal conductivity of gasket is considerable in the heat loss reduction. On the other hand, the thermal conductivity change of magnet has no apparent effect in heat loss reduction. The position change of hot line has considerable positive effect in the reduction of heat loss near gasket region.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.894-904
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• 2008

In this study, soil samples from the Antarctic and Vladivostok, Siberia were tested in the laboratory, and specific gravity, compaction curve and grain size distribution were determined. The effect of temperature change on the thermal conductivity, unfrozen water content and compressive strength were investigated. Samples for the compressive strength test were prepared in a mold with a fixed volume to prevent swelling and the effect of temperature and water content change on the strength were compared. Results from the thermal conductivity test showed that thermal conductivity values for both soils were larger at temperatures below freezing than above freezing. The unfrozen water content dropped sharply within a temperature range of $0{\sim}-5^{\circ}C$ and then gradually decreased further up to $-20^{\circ}C$. Compressive strength test results showed various stress/deformation curves with a change in water content. Sandy soil had much larger strength than pure ice at an identical temperature, while clayey soil had a smaller strength than ice near the freezing point, but showed a larger strength at temperatures belows $-15^{\circ}C$.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.86-93
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• 2016

In this paper, heat transfer characteristics of pulsating heat pipes are investigated with the diameter and the number of tubes through the computational analysis of thermal flow. The numerical simulation includes the phase change precess with VOF model using OpenFOAM software. The numerical code is modified for the phase change to occur with saturation temperature. The numerical results are compared with the previous ones to validate the present code. The resonable results have been obtained based on the mass transfer time relaxation parameter considering the density ratio. When the ratio of length to diameter and the number of tubes are on the decrease, the thermal resistances also tends to decrease in the pulsating heat pipes. These numerical results will supply the base line data to design and to manufacture the pulsating heat pipe.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.3 no.3
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• pp.161-165
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• 2002

Ge-doped rnulticomponent oxide glasses were prepared by a conventional melting method. The change of micro structure in glasses was investigated by using PL (photoluminescence) and ESR (electron spin resonance). Before UV irradiation, the PL intensity increased according to germanium contents, but decreased the intensity as soon as UV irradiation. A changed property was recovered near it original properties when it was annealed. These photodarkening and thermal bleaching effect were observed by ESR intrument. These effect did not change the glass phase but vary only change of micro structure.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.273-278
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• 2009

The experimental study is performed to investigate the optimum design of the system dissipating properly heat from the in-situ solar panel installed on site. For this purpose, six 12-Watts panels, which are set at the different conditions of the solar panels contained phase change material, changing the array of the aluminum fin and honeycomb at the back of the panel, are tested. PCM, which has $44^{\circ}C$ melting point, is chosen in this study. In order to enhance the thermal heat from the absorbed heat in PCM, finned aluminum plate is placed. Furthermore, Aluminum honeycomb is imbedded in the back container to find if it would improve the thermal conductivity of PCM. As a result, the solar panel, which is combined with honeycomb and outward fins with PCM instead of placing the fine inward, is showing the best performance in terms of controling panel temperature and efficiency.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.45-46
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• 2017

As the environment and energy problems such as global climate change (global warming, urban heat island phenomenon) and energy depletion have come to the fore, the construction and waterproofing industry are responding more critically to the demands of global green technology and are employing more eco-friendly technologies as of recent. In this study, the application of the waterproofing material with thermal response performance in construction buildings was investigated to confirm whether the thermal performance is being properly secured by the change of the surface temperature. Experimental results showed that the surface temperature difference between before and after the application is at least 19.8℃ at the maximum 26.3℃. When the degradation rate is converted, the degradation effect of about 40% on average was confirmed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.248-251
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• 2003

In this paper, it was experimented about thermal and mechanical insulation properties of a elastic epoxy specimen. We made elastic epoxy specimen adding a ratio of 0[phr], 20[phr], 35[phr] and 53[phr] with modifier to existing epoxy. Each specimen was absorbed by 25h, 196h, 361h 484h with water. In water-absorption state, it was experimented a change of heat flows by temperature of elastic epoxy and changes of thermal expansion coefficient. Also, a hardness-change of each specimen was experimented by change of water-absorption time. In this experiment DSC (Differential Scanning Calorimetry) and TMA (Thermomechanical Analysis) were used. A temperature range of DSC was changed from -0[$^{\circ}C$] to 200[$^{\circ}C$], TMA was changed from -0[$^{\circ}C$] to 350[$^{\circ}C$]. In addition, we investigated structural analysis of water absorbed specimen using SEM (Scanning electron microscope).

• Journal of the Korean Society for Heat Treatment
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• v.34 no.5
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• pp.226-232
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• 2021

The relationship between precipitation and coefficient of thermal expansion of Al-6%Si-0.4%Mg-0.9%Cu-(Ti) alloy (in wt.%) after various heat treatments were studied by the thermodynamic analyzer (TMA) and differential scanning calorimetry (DSC). Solution heat treatment of the alloy was carried out at 535℃ for 6 h followed by water quenching, and the samples were artificially aged in the air at 180℃ and 220℃ for 5 h. The coefficient of thermal expansion (CTE) curve showed some residual strain and decreased with increasing aging temperature. The CTE curves changed sharply in the temperature range of 200℃ to 400℃, and the corresponding peak shifted for the aged samples due to the change in the precipitation behavior of the secondary phase. These transformation peaks in the aged sample are related to the volume of the precipitation of the Si phase as determined by DSC analysis. The change in CTE is mainly caused by the precipitation of the Si phase in the Al-Si alloy, and the size of the change occurs simultaneously with the size of the precipitate.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.93-98
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• 2015

Nuclear power plants has a number of valves, which are operating at a high temperature-high pressure and radiation environment conditions. Nevertheless, it is important to maintain the reliability of the valves to ensure safe operation of the nuclear power plant. However, the aging of the valves by increasing of years of plant operation and the system transients due to the sudden load change are working the failures of the reliability of the valve. In this paper, we evaluate experimentally the performance change according to the thermal aging of the valve. Results show that the valve stem and the actuator leakages were enlarged by the thermal aging.