• Journal of the Korean Society for Heat Treatment
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• v.16 no.6
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• pp.311-314
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• 2003

In Mo-Xwt%Cu compound, Physical and thermal properties were systematically evaluated in terms of Cu contents and sintering temperature. Typically Cu contents were varied from 15 to 25wt% and also the Sintering temperatures were changed from $1115^{\circ}C$ to $1350^{\circ}C$. In physical properties, Mo-15~25wt%Cu has the maximum density of 95% while Mo-20wt%Cu has the maximum thermal conductivity of 165.179[${\mu}/m^{\circ}C$] at sintering temperature of $1300^{\circ}C$. Especially, Mo-25wt%Cu has the maximum hardness of 173.4 at sintering temperature of $1150^{\circ}C$ and the maximum thermal expansion of 9.0[W/mK] as the specimen heated in the range of temperature from $50^{\circ}C$ to $400^{\circ}C$. Based on electrical conductivity measurements, the relative density increased within creasing Cu contents and the values were in the range of 100~150[W/mK].

• Progress in Superconductivity
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• v.8 no.1
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• pp.54-58
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• 2006

We have fabricated double stacked 385 filamentary Bi2212/Ag round wires which have different Ag ratios. The wires have been heat-treated at the maximum temperature($T_{max}$) of $882{\sim}896^{\circ}C$ for 0.5 h. Effect of heat treatment on critical current density and critical temperature on Bi2212/Ag round wires has been studied. Critical current density of the wire heat -treated at $890^{\circ}C$ showed 206,250 $A/cm^2$ at 4.2 K, 0 T and critical temperature of the wire was 83 K. Microstructure of the wires also has been studied via optical microscopy and SEM.

• Journal of Welding and Joining
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• v.18 no.5
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• pp.70-76
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• 2000

The effect of Post Weld Heat Treatment(PWHT) of RE36 steel for marine structure was investigated with parameters such as micro-vickers hardness, corrosion potential and corrosion current density of weld metal(WM), base metal(BM) and heat affected zone(HAZ), and both Al alloy anode generating current and Al alloy anode weight loss quantity etc. Hardness of post-weld heat treated BM, WM and HAZ is lower than that of As-welded condition of each region. However, hardness of HAZ was the highest among those three parts regardless of PWHT temperature and corrosion potential of WM was the highest among those three parts without regard to temperature and corrosion potential of WM was the highest among those three parts without regard to PWHT temperature. The amplitude of corrosion potential difference of each other three parts at PWHT temperature $550^{\circ}C$, $650^{\circ}C$ are smaller than that of three parts by As-welded condition and corrosion current density obtained by PWHT was also smaller than that of As-welded condition. Eventually, it was known that corrosion resistance was increased by PWHT. However both Al anode generating current and anode weight loss quantity were also decreased by PWHT compare to As-welded condition when RE36 steel is cathodically protected by Al anode. Therefore, it is suggested that the optimum PWHT temperature with increasing corrosion resistance and cathodic protection effect is $550^{\circ}C$.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.654-664
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• 2019

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD) circulation system are optimized to solve MHD equations for the active decay heat removal system of a prototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant to prevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulation system is adopted to remove this heat via an active system that produces developed pressure through the Lorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulating loop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of $0.02m^3/s$ at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell's equations, are solved to find the minimum input current satisfying the nominal developed pressure and flow rate according to the change of variables including the magnetic flux density and geometrical variables. The optimization shows that the rectangular-type MHD circulation system requires a current of 3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removal system.

• Journal of Surface Science and Engineering
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• v.51 no.6
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• pp.415-420
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• 2018

The possibility of an improvement in heat dissipation performance of aluminum alloy heat sink for shipboard LED luminaries through plasma electrolytic oxidation (PEO) was investigated. Four different PEO coatings were produced on aluminum alloy 5052 in silicate based alkaline solution by varying current density ($50{\sim}200mA/cm^2$). On voltage-time response curves, three stages were clearly distinguished at all current densities, namely an initial linear increase, slowdown of increase rate, and steady state(constant voltage). It was found that the increase in current density caused the breakdown voltage to increase. Two different surface morphologies - coralline porous structure and pancake structure - were confirmed by SEM examination. The coralline porous structure was predominant in the coatings produced at lower current densities (50 and $100mA/cm^2$) while under high current densities(150 and $200mA/cm^2$) the pancake structure became dominant. The coating thickness was measured and found to be in a range between about $13{\mu}m$ and $44{\mu}m$, showing increasing thickness with increasing current density. As a result, $100mA/cm^2$ was proposed as an effective process parameter to improve the heat dissipation performance of aluminum alloy heat sink, which could lower the LED operating temperature by about 30%.

• Analytical Science and Technology
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• v.28 no.5
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• pp.347-352
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• 2015

Chemical properties such as heat of formation and density of methylnitroimidazole derivatives were predicted and analyzed by using density functional theory (DFT). Successive addition of energetic nitro groups into an imidazole ring increases both the heat of formation and the density. Using the chemical property values computed by DFT, explosive performance was analyzed with the Cheetah program, and compared with those of TNT, RDX, and HMX, which are currently used widely in military systems. When both C-J pressure and detonation velocity were used as explosive performance, methyldinitroimidazole derivatives show better performance than TNT, while methyltrinitroimidzole is almost close to RDX. Since methylnitroimidazole derivatives have a good merit, i.e. low melting point for melt loading, they are forecasted to be used widely in various military and civilian application.

• Fire Science and Engineering
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• v.21 no.1 s.65
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• pp.74-81
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• 2007

In this study, we have evaluated the hazardous factors of fires such as heat release rate, smoke density, ignition temperature, and flammability of carpet and curtain used in the public facilities. As a result of flame retardant treatment, the heat release rate of materials treated with flame retardant was lower than that of not treated. However, the smoke density of treated materials was higher than that of not treated. Also, we have investigated the fire characteristics of used and unused carpet. As a result, the heat release rate and the smoke density of used for 3 years carpet were higher than those of unused carpet. The distinct differences of flammability and ignition temperature between used and unused carpet were confirmed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.8
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• pp.547-555
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• 2008

The effects of paper properties such as density, air permeability, water vapor transmission rate on the thermal performance of plate-type enthalpy exchanger were experimentally investigated. Papers having different properties were made from the same pulp by calendering or refining. Enthalpy exchanger samples were made from the papers, and were tested according to the standard test procedure (KS B 6879). Effective efficiencies were obtained, which accounted for the air leakage between supply and exhaust streams. Results showed that paper density affected the sensible heat transfer of the samples. Sensible heat transfer increased with density of the paper. It was also shown that effective efficiency of latent heat transfer was approximately the same independent of the samples, which suggests that papers made of the same pulp show similar water vapor transmission characteristics independent of the degree of calendering or refining. Best performance was obtained for the sample having highest paper density and moderate water vapor transmission ratio.

• Journal of the Korea Furniture Society
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• v.23 no.2
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• pp.163-168
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• 2012

Specimens of seven hardwood species were heat-treated at three temperature levels of 170, 190 and $210^{\circ}C$. Their FSP's were measured by the volumetric swelling method and compared with the control's. Within a species the FSP decreases as the temperature of heat treatment increases. The FSP's of the controls range from 26.1 to 29.6%, while those of the specimens heat-treated at $210^{\circ}C$ from 16.9 to 21.8%. There were no difference of basic density between the heat-treated and control specimens. The color indexes of ash and beech specimens were measured using a colorimeter. It was revealed that the temperature of heat treatment affected on the color more than the treatment time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.411-422
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• 1998

In this study, experiments were carried out to provide nucleate pool boiling heat transfer data for a plain tube and 4 different low fin tubes employing 2 refrigerant mixtures of R410A, R407C, and 12 pure fluids. Low fin tubes were machined on a 19.05mm nominal outside diameter copper block according to the manufacturer's low fin tube specifications. Cartridge heaters were used to generate uniform heat flux on the tubes. For all refrigerants, heat flux varied from 10㎾/$\m^2$ to 80㎾/$\m^2$. It is found that heat transfer coefficients(HTCs) of high vapor pressure refrigerants are usually higher than those of low pressure fluids. On the other hand, the fin effect was more prominent with low pressure refrigerants than with high pressure ones. Optimum fin density as well as the increase in heat transfer coefficient with the increase in fin density were found to be strongly fluid dependent. HTCs of Rl23, a low pressure alternative refrigerant, were similar to those of Rll while HTCs of R134a, an intermediate pressure alternative refrigerant, were roughly 20% higher than those of Rl2. Finally, HTCs of R32, R125, R143a, and R410A were all higher than those of R22 by 30~50%.