• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.237-245
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• 1997

A study was conducted to examine the effects of In addition on the precipitation behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry, transmission electron microscopy and micro-hardness tester. DSC analysis was measured over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $2{\sim}20^{\circ}C$/min. The heat evolution peaks due to the formation of GP zone and ${\delta}$'phase shift to higher temperature and the peaks to $T_1$ and ${\theta}$'phases shift to lower temperature by In addition. From this result, it was proved that the formation of GP zone and ${\delta}$'phase is suppresed whereas that of $T_1$ and ${\theta}$'phases are accelerated by the In addition of 0.15wt%. The age hardening curve aged at $190^{\circ}C$ showed that the In bearing alloy(alloy B) has more faster age hardening response and a higher peak hardness than In-free alloy(alloy A), attributed to the fine and homogeneous distribution of $T_1$ and ${\theta}$'phases. The activation energies for the formation of ${\delta}$'phase in In-free and In-bearing alloys are 22.3kcal/mol and 18.6kcal/mol, respectively. Those for $T_1(+{\theta}^{\prime})$ phase of In-free and In-bearing alloys are 24.3 and 37.5kcal/mol, respectively. Quenched-in excess vacancies play an important role to the formation of precipitates.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.69-74
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• 2017

In the current machining industry, machining precision is necessary and machining is being carried out. In this ultra-precision machining industry, the fixation of the workpiece is very important and the degree of machining depends on the degree of fixation of the workpiece. In ultra-precision machining, various methods, such as using a vise chuck or the like and using bolt nut coupling, are used for fixing a workpiece to an existing machine tool. In particular, when the precision gripping force of the jig is insufficient during machining of the ultra-precision mold parts, the machining material shakes due to the vibration or friction, and the machining precision is lowered. In the ultra-precision machining of power transmission parts, such as gears, the accuracy of the product is then determined. In addition, the amount of heat generated during machining has a significant effect on the machining accuracy. This is because the vibration value changes according to the grasp force of the jig that fixes the workpiece, and the change in the calorific value due to the change in the main shaft rotation speed of the ultra-precision machining. The increase in the spindle rotation speed during machining decreased the heat generation during machining, and the machining accuracy was also good, and it was confirmed that the machining heat changed according to the fixed state of the workpiece and the machining accuracy also changed. In this study, we try to optimize the driving part of the power vise by using structural analysis, rather than the power vise, using the basic mechanical-type power unit.

• Journal of the Korean Solar Energy Society
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• v.28 no.3
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• pp.35-44
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• 2008

In this study, the experiment of the measuring of four different types of flooring materials' thermal characteristics was conducted and examined during the summer. The experimental materials were arranged on the existing slab of the roof, and then its thermal characteristics were examined from the point of view of thermal radiation analysis. The aim of this study is ultimately to draw the fundamental data for improvements in a building's thermal function and reduce the urban heat island phenomena through optimizing the thermal characteristics of the surface covering materials of a building. The results from this study are as follows; 1) Each experimental material's albedo was calculated as 0.83 on the aluminum panel, 0.40 on the rock block, 0.37 on the wood deck and 0.21 on the concrete. It shows that the concrete material, which has the lowest short wave reflective rate, absorbed the most radiation energy and the aluminium panel has absorbed the lowest radiation energy. 2) From the each experimental object's value of the long wave radiation, the concrete material measured the highest, at $628W/m^2$, and the aluminium panel measured the lowest at $412W/m^2$. Therefore, it verifies that the experimental objects' own radiation rate determines the amount of the long wave radiation. 3) The degree of energy absorbency of a building's surface covering materials is greatly influenced by its own albedo and radiation rate, Therefore, it needs to be considered for the improvements in a building's thermal function and reducing the urban heat island phenomena. 4) According to the evaluation result of the each experimental object's overall heat transmission screening function on the roof of a building, the wooden deck is proven to be an excellent material for excluding the outside temperature differences effectively with its characteristic of low heat capacity and conduction. Also its surface temperature on the roof slab and the temperature difference during the day were both measured at low.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2008.11a
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• pp.422-427
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• 2008

The major cause of Concrete Spalling at high temperatures can be divided into the Vapor Pressure Rising, caused by the increase in free water temperature within the concrete, and Pore Pressure Rising induced by the vapor moving into dense pores within the concrete. Although the occurrence of spalling within concrete caused by these pressure increases can be assessed experimentally, a close examination into Mechanistic influence against various spalling factors shall be carried out first by using Mathematical Modeling and Theoretical Equations. The Spalling Prospect Process by theoretical mechanism is expedited in order of the following; selection of heating condition (fire strength and flame heating direction), a selection of constituent elements, an analysis of heat transmission, an analysis of moisture movement, distribution of water content, an analysis of pore/vapor pressure, and assessment of spalling occurrence.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1229-1231
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• 1995

XLPE cable, which has excellent electrical and thermal performance, has been widely used for HV transmission & distribution lines. The most important thing to produce the cable products having good performance is to set the optimal operating conditions of cable machinery. Because it is very difficult to measure the temperature of cable under curing process practically, it is necessary to evaluate the cable temperature by using the method to simulate real conditions numerically. In this work, We investigate the basic theory on transient heat transfer between curing tube and cable for making a numerical simulation program using computer. In this program, a differential equation is approximated by a infinite differential method and a few assumptions are used to simplify the model and minimize the calculation time of program.

• Architectural research
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• v.15 no.4
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• pp.201-206
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• 2013

Special attention is required for the design of windows due to their high thermal vulnerability. This paper examines the problems that might arise in the application of the u-value, by reflecting the changes in the u-value of the window, depending on the window-to-wall ratio obtained in an energy demand analysis. Research indicates that the u-value of a window increases with an increase in the difference between the u-values of the frames and the glass. Relative to the changes in the u-value of the windows, the energy demand varied from 1.3% to 9.3%. Windows with a g-value of 0.3 or 0.5 displayed a higher energy demand than windows with a g-value of 0.7. Therefore, when the difference between the performance of the glass and the frame is significant, especially when the g-value is small, a modified heat transmission coefficient should be applied to the window size during the evaluation of the building energy demand.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.481-489
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• 1994

The $SnO_2$/(n)Si solar cell was fabricated by electron beam evaporation method, and their properties were investigated. In proportion to increase of substrate and annealing temperature, the conductivity of $SnO_2$ thin film was increased, but its optical transmission decreases because of increasing optical absorption of free electrons in the thin film. $SnO_2$/Si Solar cell characteristics were improved by annealing, but the solar cells was deteriorated by heat treatment above 500[.deg. C]. The optimal outputs of $SnO_2$/Si solar cell through above investigations were $V_{\var}$:350[mV], $J_{sc}$ ;16.53[mA/c $m^{2}$], FF;0.41, .eta.=4.74[%]

• 전기의세계
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• v.25 no.5
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• pp.79-87
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• 1976

This paper is to investigate the A.C generation of MHD engine, converting directly the kinetic energy of conductive gas in high temperature to electric power by the effect of magnetic field. It is known that there are at least two kinds of method in A.C MHD power generation; one, by sending stationary plasma flow in an alternating or rotating magnetic field and the other, by transmission of pulse type plasma flow in uniform and constant magnetic field, former method is adopted here. In order to raise the total efficiency of close cycle in combination with nuclear power and MHD genertaion, an argon plasma jet is utilized as heat source, which is not mixed with the seed material, and the design data are obtained for A.C MHD generation in small capacity, but induced voltage and power output have the maximum values, 15 voltages and 7.5W respectively due to plasma flow with low conductivity and weak magnetic field.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1235-1239
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• 1997

Sodium niobate single crystals were grown by high temperature solution growth with Na2O/B2O3 flux. The phase transitions and domain structures of sodium niobate were observed using transmission polarizing microscope from room temperature to $650^{\circ}C$. There was imperfect extinction region within as-grown crystals and this area could be removed by heat treatment. The area existed within crystal till 3$65^{\circ}C$, in which temperature the space group of sodium niobate is changed from Pbma to Pmnm. The phase transition from Pbma to Pmnm happened abruptly with changing domain structure. At 48$0^{\circ}C$, 52$0^{\circ}C$ and 572$^{\circ}C$, the colors and walls of domains were changed. All domains disappeared and the space group of sodium niobate was changed from P4/mbm to Pm3m at 64$0^{\circ}C$. When sodium niobate changed from high temperature phase to low temperature phase, the memory effect of domain structure was not observed.

• Journal of Biosystems Engineering
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• v.15 no.3
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• pp.167-176
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• 1990

This study was carried out to develop a process to design a stirling engine utilizing agricultural energy resources and to understand problems confronted in manufacturing the engine in domestic environments, and to suggest methods to improve performance of the engine. A small prototype of the engine was designed, manufactured and tested for its performance. The study proved that more work would be needed to develop a method to seal the engine and to make the engine cooler. Performance of the engine was a little inferrior to that of the GPU-3 engine and was expected to be enhanced by improvement of heat transfer and power transmission mechanisms.