• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.1
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• pp.31-37
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• 2019

This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1474-1476
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• 2005

ZnO:Al(AZO) has been investigated for the photovoltaic cell or TCO(Transparent Conductive Oxide) of the display, because it has good electrical and optical properties. In this study, the ZnO:Al(AZO) thin film prepared on variation of substrate temperature by FTS(Facing Targets Sputtering) system. In case of TCO, because resistivity and roughness values affect the lighting of the OLED, their factors are very important. Therefore, in this paper, the electrical and optical properties of the AZO thin film were investigated with the deposition conditions and its roughness was investigated on variation of the substrate temperature. In results, AZO thin film deposited with the transmittance over 80% and the resistivity was reduced from $1.36{\times}10^{-3}$ [O-cm] to $4{\times}10^{-4}$ [O-cm] with increasing the substrate temperature from R.T to $200[^{\circ}C]$. Especially, we could obtain the resistivity $4{\times}10^{-4}$ [O-cm] of AZO thin film prepared at working pressure 1[mTorr], input current 0.4[A] and substrate temperature $200[^{\circ}C]$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.2
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• pp.79-82
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• 1984

Seasonal and secular variations of water temperature in Chungmu port were investigated with the data obtained from the Technical Reports(1976~1983) of Hydrographic Office. Monthly and annual range of water temperature were 2 to 8$^{\circ}C$ and 18 to 21$^{\circ}C$, respectively. The coefficients of variance of monthly mean water temperature were 0.015(February, 1976) to 0.208(December, 1980) and their values were smaller in the summer season than in the winter season. The result of harmonic analysis for investigating the seasonal variation of water temperature was T(t)=15.66+8.06 cos(10$^{\circ}$t-233.5)+0.92 cos(20$^{\circ}$t-216). The periods of secular variation were about 2 years and 3 years.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.1 no.2
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• pp.1-6
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• 2005

Ground water source heat pumps are clean, energy-efficient and environment-friendly systems for cooling and heating. Although the initial cost of ground water source heat pump system is higher than that of air source, it is now widely accepted as an economical system since the installation cost can be returned within a short period of time due to its high efficiency. In a ground water source heat pump system, the variation of the ground water temperature is an important factor that influences the system performance. In this study, variation of the ground water temperature of a single well system is studied experimentally for various operating conditions. When ground water flow exists in the underground, the returned water exchanges heat efficiently with the ground and the temperature of the ground water remains nearly constant. Hence the short circuit problem is minimized. If an active flow of ground water flow exists in the underground, a singe well heat pumps system will be free of short circuit problem and can operate with high performance.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.3
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• pp.328-333
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• 2019

During the winter of 2017/2018, significantly low water temperatures were detected around the western and southern coasts of Korea (WSCK). In this period, sea surface temperature (SST) in the Korea Waters was about $2^{\circ}C$ lower than mean temperature. Using the real-time observation system, we analyzed the temporal variation of SST during this period around the western and southern coasts. Low water temperature usually manifested over a period of about 10 ~ 20 days. The daily Arctic oscillation index was also similarly detectable with the variation of SST. From the cross-correlation function, we compared two periodic variations, which were SST around the WSCK and the Arctic oscillation index. The cross correlation coefficients between both variations were approximately 0.3 ~ 0.4. The time lag of the two time series was about 6 to 7 days. Therefore, significantly low water temperatures during winter in the Korean coastal areas usually became detectable 6 to 7 days after the negative peak of Arctic oscillation.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.243-248
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• 2001

The objective of this study is to investigate the thermal conductivity of cement mortar for apartment housing floor using expansive admixture, copper fiber, cower lathe, hollowed aluminum plate. According to test results, temperature at point (a) located above heating pipe does not show significant variation with age, and temperature at (b), which is located at the finishing surface above heating pipe, and temperature at (c), which is located at center surface between heating pipe has remarkable change. Temperature distribution sat (b) are in order for, structure containing copper fiber>plain structure>structure containing hollowed aluminum plate>structure containing expansive admixture. Temperature distribution, shows high tendency in order for, structure containing copper fiber>structure containing copper lathe>structure containing hollowed aluminum plate>plain structure>structure containing expansive admixture. (a) estimation of temperature distribution is determined with the variation of temperature between (b) point and (c) point during 60 minutes heating.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2000.05a
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• pp.26-33
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• 2000

This study was conducted to investigate the relationships between yearly variations of elimatic elements and yearly variations of productivity in potato. In addition, correlation coefficients among yield and yield components were estimated. The data of yield and yield components were investigated for 9 years from 1987 to 1995. The meteorological data what gathered at the Goheung Weather Station for the same period of crop growing season were used to find out the relationships between climatic elements and crop productivity. Yearly variation of the daily minimum temperature in March and April were large with coefficients of variation (C.V.) of 126.0%, 368%, respectively, but the variation of the daily mean and maximum temperature in May and June were relative small. Stem length and number of stem show more C.V. of 9.3%, 14.3%, respectively, but the variation of the yield was relative small with 3.7%. Correlation coefficients between the amount of precipitation in April and yield, yield and daily mean temperature in June were negatively significant at the level of 5, 1 %, respectively. Correlation coefficients between the growth habits and yield are positively significant at the level of 5, 1 %, respectively. Simple linear regression equations by the least square method are estimated for stem length (Yl) and the precipitation in April(X) as Y,=82.47-0.11x (R2=0.3959), and for yield(Y2) and the precipitation in April(X) as Y,=2003.61-0.94X (R2=0.5418).

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.1-11
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• 2002

The suitable turbulence model is found to be required in the course of establishing a proper analysis methodology for thermal stripping phenomena which are shown in strong temperature variation area such as reactors and propulsion devices. Three different turbulence models of $\kappa$-$\varepsilon$ model, modified $\kappa$-$\varepsilon$ model, and full Reynolds stress(FRS) model, are applied to analyze unsteady turbulent flows with temperature variation. Three test cases are selected for verification. These are vertical jet flows with water and sodium, and parallel jet flow with sodium. Analysis yields the conclusion that 3-D computation with FRS betters others. However, modified modeling is required to improve its heat transfer characteristic analysis. Further analysis is performed to find momentum variation effects on temperature distribution. It is found that the momentum increase results increase of fluid mixing and magnitude of temperature variation.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.300-303
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• 2008

In the present study, the simple form of the heat transfer equation were suggested to estimate the temperature variation inside the oil pipe in order to determine the thickness of the insulating materials to retain the working oils below the critical temperature. The conservation of the thermal energy at arbitrary time were modeled to one dimensional unsteady equation with the empirical formula or data. The calculating results for non-insulation case showed that the temperature were very sensitive to the thermal convection by the velocity of the external wind. For insulation case, the insulation material which has higher density and specific heat, lower thermal conductivity should be chosen with more brighter coloring outside the pipe in order to retain the working oils below the critical temperature.

• Structural Engineering and Mechanics
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• v.6 no.3
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• pp.275-289
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• 1998

The objective of the paper is to present a method whereby the time required for a steel structure to sustain the effects of a prescribed temperature rise according to real fire curves can be calculated. The method is divided into two parts. The first part deals with the post-yield behaviour of steel structures at elevated temperatures. It takes into account the variation of the properties of steel material with temperature in an incremental elastoplastic analysis so that the safety factor of the structure under certain fire conditions can be assessed. The second part deals with the heat transfer problem of bare steel members in real fire. Factors affecting the heat transfer process are examined and a model for predicting the temperature variation with time under real fire conditions is proposed. This model results in more accurate temperature predictions for steel members than those obtained from previously adopted model.