• Journal of the Korean Society for Heat Treatment
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• v.17 no.4
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• pp.223-229
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• 2004

The effects of the cooling and annealing conditions on the microstructures and corrosion properties were investigated for the Cu-contained Zr-Nb alloy (Zr-1.1Nb-0.07Cu). After annealing at $1050^{\circ}C$ for 15 min, the specimens were cooled by three methods of water quenching, air cooling, and furnace cooling. Widmanstatten structures were developed in both air- and furnace-cooled specimens, and the Widmanstatten plate width of the furnace-cooled specimens was wider than that of the air-cooled ones. The weight gain in the furnace-cooling case was higher than that in the air-cooling case. This could be the reason why the diffusion time was more enough during the furnace cooling than the air cooling. The oxide of the furnace-cooled specimen was nonunformly formed just beneath the Widmanstatten plate boundaries, where ${\beta}_{Zr}$ phases were exised concentrately. Compared with the $640^{\circ}C$ annealing after the water quenching, the $570^{\circ}C$ annealing could make the ${\beta}_{Nb}$ phases and a concomitant reduction of the Nb in the matrix, and then it could improve the corrosion resistance with the increase of the annealing time. It would be concluded that the corrosion resistance of the Zr-1.1Nb-0.07Cu was good when the Nb concentration in the matrix was reached at an equilibrium level and then the ${\beta}_{Nb}$ phase was formed.

• Korean Journal of Materials Research
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• v.34 no.1
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• pp.44-54
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• 2024

High-Manganese (Mn) austenitic steel, with over 24 wt% Mn content, offers outstanding mechanical properties in cryogenic settings, making it a potential replacement for existing cryogenic materials. This high manganese steel exhibits high strength, ductility, and wear resistance, making it promising for applications like LNG tanks, flanges, and valves. To operate in cryogenic environments, hot forging and heat treatment processes are vital, especially in flange production. The cooling rate during high-temperature cooling after hot forging plays a critical role in influencing the microstructure and mechanical properties of high manganese steel. The rate at which cooling occurs during this process influences the size of the grains and the distribution of manganese and consequently has an impact on mechanical properties. This study assessed the microstructure and mechanical properties based on different cooling rates during the hot forging of High-Mn steel flanges. Comparing air and water cooling after hot forging, followed by heat treatment, revealed notable differences in grain size. These differences directly impacted mechanical properties such as tensile strength, hardness, and Charpy impact property. Understanding these effects is crucial for optimizing the performance and reliability of High-Mn steel in cryogenic applications.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.1
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• pp.33-38
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• 2010

Developments of numerical methods are very important to design and analysis for a high subsonic turbine blade. In general, Analysis by experimental investigation has needed a lot of human resources and required time, indispensably, and equipments still have a limit to measure in conditions of high temperature. Rapid technological developments of CPU and integration level of memory make it possible to advance computation with almost exactly simulation so, recent developments of numerical methods are in spotlight. In the present study, the panel method, which is well-known as relatively simplified numerical method, and 2-dimensional ordinary differential Falkner-Skan equation were computed in order to analyze the outer flow, and FVM-based solid heat transfer equation, was also computed to forecast the temperature distribution of the airfoil and the turbine blade. Unstructured grid was constructed in the turbine blade, which has double cooling holes, in order to analyze the internal heat transfer. Cooling fluid was assumed as fully-developed turbulent flow and that circulated in cooling holes.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.865-871
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• 2006

In order to examine and compare the characteristics of two vitrified forms (AG8W1 and DG2) simulated for the operation of a commercial vitrification facility being constructed in Ulchin nuclear power plant, the vitrified forms were cooled by the natural cooling and annealing methods respectively. And the Product Consistency Test (PCT), compressive strength, thermal conductivity, specific heat, phase stability, softening point and Coefficient of Thermal Expansion (CTE) of the vitrified farms were experimented. Consequently, it was shown that there were no significant differences on the physiochemical properties of the vitrified forms performed the natural cooling and annealing.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.142-148
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• 2018

To improve the performance of a launch vehicle, kerosene, a launch vehicle fuel, undergoes a densification process. Liquid nitrogen injection cooling is an effective densification method which has a simple system and is inexpensive. During the cooling process, however, nitrogen may dissolve in the kerosene, possibly resulting in changes to fuel properties. Therefore, it is essential to measure and eliminate the amount of dissolved nitrogen in the kerosene. In this study, the vacuum extraction principle is introduced to measure the content of dissolved nitrogen in the kerosene. In addition, the experimental results, which used a designed/manufactured nitrogen sampling device, are described. From the results, the validity of the nitrogen sampling device and the dissolved nitrogen measurement/elimination methods was demonstrated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1418-1423
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• 2004

High speed machining experiment on the heat-treated mold steel(STAVAX and CALMAX of hardness HRc 53) is carried using TiAlN coated ball endmill. Tool life and wear characteristics under the various machining parameters and cooling methods are investigated. Effect of cooling method on life and wear of the tool was compared. For most cases, tool life was not determined by the amount of wear but by th chipping on the cutting edge. It is found that tool manufacturer's cutting parameters generally agrees with the results of this experiment.

• Proceedings of the Korean Society for Bio-Environment Control Conference
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• 1999.11a
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• pp.130-133
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• 1999

우리나라의 시설재배는 비가림 형태에서 많은 자본과 기술이 투자된 현대화 고정시설로 발전해가고 있으며 면적도 증가하고 있다. 시설의 활용면에서는 주로 동절기에 집중되어 있고, 하절기에는 최고기온이 3$0^{\circ}C$ 이상되는 날이 2-3개월 정도로 시설내 작물재배는 거의 불가능한 실정이다. 따라서 하절기에는 대부분 휴작함으로서 시설의 주년이용에 문제점으로 대두되고 있다. (중략)

• Journal of Bio-Environment Control
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• v.9 no.1
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• pp.1-10
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• 2000

This study was performed to find an efficient method to overcome extremely high temperature in greenhouses during summer season. The actual utilization of greenhouses during hot summer season showed that about 21.6％ of the investigated greenhouse farms were in fallow state, and most of greenhouse farms were cultivated under the very inferior environment. Thermal environment of greenhouses according to the evaporative cooling method and several assistant cooling methods such as ventilation, shading screen, roof sprinkling were examined. As the each assistant cooling method was used, about 74.8％, 25.9％, and 58.2％ of temperatures measured at intervals of ten minutes between ten and seventeen o'clock were above 35$^{\circ}C$. When shading screen and evaporative cooling system were operated, most greenhouse air temperatures were maintained below 35$^{\circ}C$, and showed a drop of 3.8~4.2$^{\circ}C$ as compared with naturally ventilated greenhouse.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.61-67
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• 2017

As transistor density increases rapidly, a heat flux from IC device rises at fast rate. Thermal issues raised by high heat flux cause IC's performance and reliability problems. To solve these thermal management problems, the conventional cooling methods of IC devices were reached their thermal limit. As a result, alternative cooling methods such as liquid heat pipe, thermoelectric cooler, thermal Si via and etc. are currently emerging. In this paper microchannel liquid cooling system with TSV was investigated. The effects of 2 coolants (DI water and ethylene glycol 70 wt%) and 3 metal bumps (Ag, Cu, Cr/Au/Cu) on cooling performance were studied, and the total heat flux of various coolant and bump cases were compared. Surface temperature of liquid cooling system was measured by infrared microscopy, and liquid flowing through microchannel was observed by fluorescence microscope. In the case of ethylene glycol 70 wt% at $200^{\circ}C$ heating temperature, the total heat flux was $2.42W/cm^2$ and most of total heat flux was from liquid cooling effect.

• Bulletin of the Korean Chemical Society
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• v.21 no.3
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• pp.281-290
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• 2000

We varied recombination method of fenetic algorithm (GA), i.e., crossover step, to compare efficiency of these methods, and to find more optimum GA method. In one method (A), we select two conformations(parents) to be recombined by systematic combination of lowest energy conformations, and in the other (B), we select them in a ratio proportional to the energy of the conformation. Second variation lies in how to select crossover point. First, we select it randomly(1). Second, we select range of residues where internal energy of the molecule does not vary for more than two residues, select randomly among such regions, and we select either thr first (2a) or the second residue (2b) from the N-terminal side, or the first (2c) or the second residue (2d) from the C-terminal side in the selected region for crossover point. Third, we select longest such hregion, and select such residue(as cases 2) (3a, 3b, 3c or 3d) of the region. These methods were tested in a 2-dimensionl lattice system for 8 different sequences (the same ones used by Unger and Moult., 1993). Results show that compared to Unger and Moult's result(UM) which corresponds to B-1 case, our B-1 case performed similarly in overall. There are many cases where our new methods performed better than UM for some different sequences. When cooling factor affecting higher energy conformation to be accepted in Monte Carlo step was reduced, our B-1 and other cases performed better than UM; we found lower energy conformers, and found same energy conformers in a smaller steps. We discuss importance of cooling factor variation in Monte Carlo simulations of protein folding for different proteins. (A) method tends to find the minimum conformer faster than (B) method, and (3) method is superior or at least equal to (1) method.