• Journal of Welding and Joining
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• v.34 no.5
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• pp.70-76
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• 2016

In this study, Microstructure and tensile properties in arc brazed joints of 1000MPa grade DP steel using Cu-Si insert metal were investigated. The fusion zone was composed of Cu phase which solidified a little Fe and Si. The former phase formed due to dilute the edge of base material by arc, although Fe was not solid solution in Cu at the room temperature. Cu3Si particles formed by crystallization at $1100^{\circ}C$ during faster cooling. After the tensile shear test, there are no differences between the brazed joint efficiencies. The maximum joint efficient was about 37% compared to strength of base metal. It is better than that of arc brazed joint of DP steel using Cu-Sn filler metal. Fracture position of all brazing conditions was in the fusion zone. Crack initiation occurred at three junction point which was a stress singularity point of upper sheet, lower sheet and the fusion zone. And then crack propagated across the fusion zone. The reason why the fracture occurred at fusion zone was that the hardness of fusion zone was lower than that of base material and heat affected zone. The correlation among maximum load and hardness of fusion zone and EST at fractured position was $R^2=0.9338$. Therefore, this means that hardness and EST can have great impact on maximum load.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.232-237
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• 2016

Cocrystallization of active pharmaceutical ingredients has been widely recognized as a versatile tool to regulate the physical properties of pharmaceutical compounds through designed crystal structures. Grinding or milling has been especially useful to screen the feasibility of cocrystal formation, and the addition of a small amount of liquid is routinely necessary. In the present study, the effect of temperature was studied for the milling cocrystallization of ibuprofen and nicotinamide to establish a liquid-free method. The milling-induced cocrystallization was more effective with liquid nitrogen cooling than at room temperature, which was confirmed by XRD and DSC analyses. This behavior was attributed to the limited molecular mobility below the glass transition temperatures of the cocrystal components, which made it effective to destruct the crystals of raw materials and consequently form the ibuprofen/nicotinamide cocrystal. Further studies would be necessary to establish the utility of the current conclusion to the field of pharmaceutical crystallization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.759-766
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• 2011

Recently, noise reduction in room air conditioners has been one of the important issues as well as cooling efficiency. The rotary compressor is the dominant noise source in an air conditioner. A number of studies have been conducted on reducing compressor noise through improving muffler and resonator design. However the noise from the accumulator, a noise delivering path between compressor and air conditioner, is not fully taken into consideration. The accumulator contains a large inner cavity, and usually generates additional resonance noise during operation. This paper aims to conduct an optimal design for reducing accumulator noise by maximizing the transmission loss within the target frequency range that represents high-order nonlinearity. Design of experiments and radial basis function neural network are used in the context of approximate meta-models, and genetic algorithm is used as an optimization tool.

• Journal of the Korean Society of Marine Environment & Safety
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• v.12 no.4 s.27
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• pp.267-272
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• 2006

Butterfly valves have been used for shut-off and throttling-control application in many industrial fields. Recently, they are frequently used for cooling water, oil system and ballast piping system of many larger vessels. They are especially suited for flow throttling control of heat exchangers in engine room. Measurement by the PIV(Particle Image Velocimetry) was conducted to investigate the flow characteristics of butterfly valve inserted within circular pipe. Flow behaviors such as instantaneous and time-mean velocity vectors are investigated. Furthermore, to reveal systematic performance of the butterfly valve, wall pressure was measured at 6 points along the pipe by digital manometer. As the valve position moves to the closed side, flow separation increases and persists its tendency downstream until smoothly uniform flow developed. The pressure loss is found to be about zero for the disk open angles less than 45 degrees, but is substantially increased for those larger than 60 degrees.

• Progress in Superconductivity and Cryogenics
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• v.15 no.4
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• pp.53-58
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• 2013

KSTAR in-vessel cryo-pump has been installed in the vacuum vessel top and bottom side with up-down symmetry for the better plasma density control in the D-shape H-mode. The cryogenic helium lines of the in-vessel cryo-pump are located at the vertical positions from the vacuum vessel torus center 2,000 mm. The inductive electrical potential has been optimized to reduce risk of electrical breakdown during plasma disruption. In-vessel cryo-pump consists of three parts of coaxial circular shape components; cryo-panel, thermal shield and particle shield. The cryo-panel is cooled down to below 4.5 K. The cryo-panel and thermal shields were made by Inconel 625 tube for higher mechanical strength. The thermal shields and their cooling tubes were annealed in air environment to improve the thermal radiation emissivity on the surface. Surface of cryo-panel was electro-polished to minimize the thermal radiation heat load. The in-vessel cryo-pump was pre-assembled on a test bed in 180 degree segment base. The leak test was carried out after the thermal shock between room temperature to $LN_2$ one before installing them into vacuum vessel. Two segments were welded together in the vacuum vessel and final leak test was performed after the thermal shock. Commissioning of the in-vessel cryo-pump was carried out using a temporary liquid helium supply system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2183-2190
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• 2000

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.246-249
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• 2013

Nano-sized ${\beta}$-SiC nanoparticles were synthesized combined with a sol-gel process and a carbothermal process. TEOS and carbon black were used as starting materials for the silicon source and carbon source, respectively. $SiO_2$ nanoparticles were synthesized using a sol-gel technique (Stober process) combined with hydrolysis and condensation. The size of the particles could be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The average particle size and morphology of synthesized silicon dioxide was about 100nm and spherical, respectively. The average particles size and morphology of the used carbon black powders was about 20nm and spherical, respectively. The molar ratio of silicon dioxide and carbon black was fixed to 1:3 in the preparation of each combination. $SiO_2$ and carbon black powders were mixed in ethanol and ball-milled for 12 h. After mixing, the slurries were dried at $80^{\circ}C$ in an oven. The dried powder mixtures were placed in alumina crucibles and synthesized in a tube furnace at $1400{\sim}1500^{\circ}C$ for 4 h with a heating rate of $10^{\circ}C$/min under flowing Ar gas (160 cc/min) and furnace cooling down to room temperature. SiC nanoparticles were characterized by XRD, TEM, and SAED. The XRD results showed that high purity beta silicon carbide with excellent crystallinity was synthesized. TEM revealed that the powders are spherical shape nanoparticles with diameters ranging from 15 to 30 nm with a narrow distribution.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.808-815
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• 1995

The magnetic states of nonstoichiometric substituted ferrite Fe$_{}1.429$(Al$_{4-x}$ Ga$_{x}$)$_{0.286}$ Si$_{0.143}$ /O$_4$ system have been investigated using Mossbauer spectroscopy and SQUID. The Mossbauer spectra at room temperature show well-defined two Zeeman patterns for x=0.2, superpositions of two Zeeman patterns and a doublet for x=0.4. The doublet peak seems to be originated from the superparamagnetic clusters. The system shows significant departures from the Neel's collinear model and seems to be the diluted ferrites. The Mossbauer spectra below R.T show various and complicated patterns, which can be explained by freezing of the superparamagnetic clusters. On cooling, magnetic states of the system may be various and multicritical, Resulting from SQUID measurements, there was an unexpected dip in magnetization curves below 50K. It was interpreted as an effect of spin canting including spin freezing or collective spin behavior.

• Korean Journal of Food Science and Technology
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• v.18 no.4
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• pp.319-324
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• 1986

The characteristics of cooked rice were investigated with variation in amount of water added and different cooking methods of pressure and electric cookers. Samples added with 1.3, 1.5, and 1.7 times of water were evaluated for sensory characteristics and for degree of gelatinization by enzyme digestion method upon one hour cooling at room temperature. Samples were reheated by microwave oven and then compaired with fresh samples through sensory evaluation under the same condition. Sensory attributes of rice cooked with 1.3, 1.5, and 1.7 times of water addition showed significant differences among the groups in most properties except in stickiness. Degree of gelatinization in fresh samples also indicated significant differences between the two cookers in varied rice to water ratio. There were significant differences among the samples, fresh and reheated by microwave oven. Revealed differences, however, were not great in the same type of cooker groups.

• Progress in Superconductivity
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• v.4 no.1
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• pp.86-89
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• 2002

In this paper, the design of a IMVA single-phase high temperature superconducting(HTS) power transformer with BSCCO-2223 HTS tapes is presented. The rated voltages of each sides of the transformer are 22.9 ㎸ and 6.6 ㎸, respectively The winding of 1MVA HTS transformer is consisted of double pancake type HTS windings, which have advantages of insulation and distribution of high voltage, and are cooled by subcooled liquid nitrogen of 65K. Four HTS tapes were wound in parallel for the windings of low voltage side and the four parallel conductors are transposed. The design of 1MVA HTS transformer, a shell type core made of laminated silicon steel plate is chosen, and the core is separated with the windings by a cryostat with a room temperature bore. The cryostat made of non-magnetic and non-conducting material and a liquid nitrogen sub-cooling system is designed in order to maintain the coolant's temperature of 65K. For electromagnetic analysis of 1MVA HTS transformer, a finite element method of an axis of symmetry is used. The maximum perpendicular component of magnetic flux density of pancake windings is about 0.15T. And through analyzing the magnetic field distribution, an optimal winding arrangement of 1MVA HTS transformer is obtained.