• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.1026-1030
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• 2010

This paper summarizes the activities performed for the development of a BLDC(Brushless Direct Current) motor driven cryogenic thrust control valve with application to KSLV-II rocket engine. The developed thrust control valve can modulate the flow rate of liquid oxygen under cryogenic temperature of 90K and high pressure of 113.2 bar with the help of electro-mechanical actuator driven by a BLDC motor. This valve can be applied to an engine combustion test after minor change because all development certification test have been performed successfully.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.1-4
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• 2008

Fuel cells have the potential of providing several times higher energy storage densities than those possible using current state-of-the-art lithium-ion batteries, but current energy density of fuel cell system is not better than that of lithium-ion batteries. To achieve the high energy density, volume and weight of fuel cell system need to be reduced by miniaturizing system components such as stack, fuel tank, and balance-of-plant. In this paper, the thin flexible PCB (Printed circuit board) is used as a current collector to reduce the stack volume. Two end plates are made from light weight aluminum alloy plate. The plate surface is wholly oxidized through the anodizing treatment for electrical insulation. The opening rate of cathode plate hole is optimized through unit cell performance measurement of various opening rates. The performances are measured at room temperature and ambient pressure condition without any repulsive air supply. The active area of MEA is 10.08 $cm^2$ and active area per a unit cell is 1.68 $cm^2$. The peak power density is about 210 mW/$cm^2$ and the air-breathing planar stack of 2 Wis achieved as a small volume of 18 cc.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.108-114
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• 2011

Steam reformer was organized with steam reforming process and CO removing process. The steam reforming process needed high temperature, 600~900 $^{\circ}C$, for catalytic-reaction which was extract of hydrogen from steam and hydrocarbon. The effects of the evaporator configuration on its heat transfer characteristics were investigated both experimentally and numerically to pursue the miniaturization. In this study, three configurations were considered where the different structures were tested; empty, embossing and mesh filled. For the comparison of heat transfer performance of shape evaporator disk, numerical analysis using SC-Tetra code and experiment were carried out. In case of reformer system design, it should be considered heat transfer rate, differential pressure and fluid flow direction.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.96-103
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• 2002

The objective of this study is to adjust the roll gap fur the dimension accuracy of bar in hot bar rolling process considering roll wear. In this study hot bar rolling processes fur round and oval passes have been investigated. In order to predict the roll wear, the wear model is reformulated as an incremental from and then wear depth of roll is calculated at each deformation step on contact area using the results of finite element analysis, such as relative sliding velocity and normal pressure at contact area. Archard's wear model was applied to predict the roll wear. To know the effects of thermal softening of DCI (Ductile Cast Iron) roll material according to operating conditions, high temperature micro hardness test is executed and a new wear model has been proposed by considering the thermal softening of DCI roll expressed in terms of the main tempering curve. The new technique developed in this study for adjusting roll gap can give more systematically and economically feasible means to improve the dimension accuracy of bar with full usefulness and generality.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1430-1431
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• 2011

To develope the transparent conducting oxide(TCO) films is one of the essential technologies to improve various properties of electro-optical devices such as dye-sensitized solar cells(DSCs). ITiO thin film is considered one of the candidates as TCO electrodes of DSCs because it shows many advantages such as the high transparency in long wavelength range above 700nm and excellent properties of electrical necking between nanoporous TiO2 and ITiO transparent electrode. This paper presents the effect of sputtering processes on the structural, electrical and optical properties of ITiO thin film deposited by r.f. magnetron sputtering. The effect of doping concentration of Ti on the chemical compounds and C axis-orientation properties of were mainly studied experimentally. The morphology and electrical properties were greatly influenced by deposition processes, especially by the doping concentration of Ti. The $3.8{\times}10^{-4}{\Omega}{\cdot}cm$ of minimum volume resistivity were obtained under the experimental conditions of gas pressure 7mTorr, substrate temperature $300^{\circ}C$, and 2.5% of Ti doping concentration.

• Carbon letters
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• v.4 no.3
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• pp.133-139
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• 2003

Carbon/carbon composites are ideal candidates for a number of aerospace applications including structural materials for advanced vehicles, leading edges, structures of re-entry and hypersonic vehicles and propulsion systems. One serious defect for such application of the carbon/carbon composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating was employed to protect the composites from oxidation. It is mechanically and chemically stable under extreme thermal and oxidative environments, provides good adhesion to the substrate, and offers good thermal shock resistance. The SiC layer on the nozzle machined from the carbon/carbon composites was formed by pack-cementation method. Then, erosion characteristic of SiC coated carbon/carbon nozzle was examined by combustion test using a liquid rocket motor. The erosion rates were measured as function of combustion pressure, ratio of oxygen to fuel, combustion time, density of the composites and geometry of reinforced carbon fibre in the composites. The morphology change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.996-1001
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• 2010

Recently, the demand of ceramic metal halide lamp has been expanded. Therefore, the lamp with high efficiency and long lifetime are increasing and the evaluation of reliability is needed. In this paper, the degradation phenomena of ceramic metal halide lamp was studied. The lamp was tested for 3000 on/off cycles with each cycle having a duration of 20 minutes on and 20 minutes off based on the accelerated aging experiment based on "Reliability Standards RS C 0085". As result, the corrosion of arc tube and leak was appeared from reaction between inner wall of PCA and chemical elements, and distortion of electrode was resulted from difference of thermal expansion between arc tube of PCA and electrode. Also, the efficiency of lamp was decreased by the change of inner pressure, operation temperature, and driving voltage from wall blackening.

• Journal of Power System Engineering
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• v.19 no.1
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• pp.24-30
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• 2015

Geothermal energy is used in various types, such as power generation, direct use, and geothermal heat pumps. Geothermal energy with high temperature have been used for power generation for more than a century. The purpose of the study is to investigate flow and electricity power characteristics of hydraulic turbine for power generation of geothermal heat pump type with closed-system. The differences between the four types of hydraulic turbine, are different from the blade shape, volume, angle and etc. In case of prototype(1), pressure at blade was reduced to 2.1 bar, the kinetic energy of blade increased by increasing flow velocity(4.1 m/s). The increase of flow velocity at the blade edge markedly appeared, to increase the kinetic energy of the rotating shaft. In case that gateway in hydraulic turbine was installed, operating torque and RPM(1,080) of the rotating shaft increased respectively. Although rotational speed of prototype(2) compared to prototype(1) was reduced, the power generation capacity was greater about 3.4 times to 97 W. The most power of 255W was generated from prototype (4).

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1533_1534
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• 2009

This paper presents an atmospheric micro glow plasma-jet device. The device consists of four components; a thin Ni anode, a porous alumina insulater, a stainless steel cathode and an aluminum case. The Ni anode is fabricated using micromachining technology. The anode has 10 holes, of which the hole diameter and the depth are $250{\mu}m$ and $60{\mu}m$, respectively. The discharge test is performed in nitrogen gas at atmospheric pressure for 20 kHz AC bias. The breakdown voltage is 3.5 kV at gas flow rate of 4 L/min and the the plasma-jet is blown out to ambient at 5.5 kV. In order to verify the characteristics of plasma, the current and the voltage of device are measured. The maximum temperature of plasma is $37^{\circ}C$. The plasma is well generated and stable at high voltage.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.3
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• pp.96-101
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• 2013

Automotive brake system is an essential element for the safety. The system is powered by the circulation of brake oil. A braker hose is used for the circulation of the oil in this system. Layout of the hose changes according to the steering and stress occur in the hose. A lot of the durability tests are performed in order to prevent serious problems such as hose bursting by the accumulation of the stress before setting an optimized hose layout on automobile. The test is conducted for the layout which is same such as set in automobile. In the test, brake hose layout shall exercise the same mode of thousands of times under the high temperature and periodic pressure condition and then the damage of the tested hose is inspected. This test, however, has a disadvantage of heavy consumption of time and money. In order to compensate for these drawbacks, the finite element method(FEM) study was performed to predict the changes in the layout of the brake hose. In this study, the FEM results and the test results were compared and the validity was verified. The radius of curvature of the FEM and test at the same positions were especially investigated for the validation. Also, this study will be used as the basis of research on the life prediction of brake hose.