• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.685-692
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• 2006

In a general centrifugal pump, if it is operated in a two-phase flow the activity of the impeller usually degrades and occasionally losses its function. However, the effect of break down of centrifugal pump due to entrained air has not been clarified yet. This paper shows the air-water two-phase flow characteristics of closed type and semi-open type impellers. In a sing1e-phase flow, closed-type impeller has higher efficiency and head. But in air-water two-phase flow semi-open type impeller's rates of decreases of efficiency and head are decreased.

• 한국공간정보시스템학회:학술대회논문집
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• 2004.05a
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• pp.161-168
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• 2004

The dynamic instability of snapping phenomena has been studied by many researchers. Few papers deal with dynamic buckling under loads with periodic characteristics, and the behavior under periodic excitations is expected to be different from behavior under STEP excitations. We investigate the fundamental mechanisms of the dynamic instability when the sinusoidally shaped arch structures are subjected to sinusoidally distributed excitations with pin-ends. The mechanisms of dynamic indirect snapping of shallow arches are especially investigated under not only STEP function excitations but also under sinusoidal harmonic excitations, applied in the up-and-down direction. The dynamic nonlinear responses are obtained by the numerical integration of the geometrically nonlinear equation of motion, and examined by Fourier spectral analysis in order to get the frequency-dependent characteristics of the dynamic instability for various load levels.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.63-67
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• 2002

In this study, the performance of the Stirling type orifice Pulse tube refrigerator (OPTR) with a linear compressor was investigated by experiment. The dynamic pressures at three points and a temperature at the cold heat exchanger are measured to explore the dependency of the orifice on the performance of the OPTR. The experimental results show that the opening of the orifice has significant effects on the no load temperature and cool down characteristics. The Pressure amplitude in Pulse tube decrease as the opening of the orifice increase, but the mass flow rate through the orifice and the electric input Power to the compressor increase. The results show that the operating frequency and charging Pressure does not affect on the no load temperature. The pressure amplitude in pulse tube decrease as the operating frequency increase or the charging Pressure decreased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.2
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• pp.137-143
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• 2008

High voltage MLCCs with C0G temperature coefficient characteristics could apply DC-DC invertor were investigated for its dielectric properties. Also we manufactured MLCC through various process and studied the characteristics of dielectric break down voltage [BDV] and dielectric property as the variation of thickness in the green sheet and how to pattern the internal electrode. As the thickness of green sheet is increase, the dielectric BDV per unit thickness is decreased. But as the pattern of internal electrodes were floated we could manufacture the high voltage MLCC maintained its dielectric BDV a unit.

• Electrical & Electronic Materials
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• v.7 no.2
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• pp.123-129
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• 1994

SONOS EEPROM chips, containing several SONOSFET nonvolatile memories of various channel size, have been fabricated on the basis of the existing n-well CMOS processing technology for 1 Mbit DRAM ($1.2\mu\textrm{m}$.m design rule). All the SONOSFET memories have the triple insulated-gate consisting of 30.angs. tunneling oxide, 205.angs. nitride and 65.angs. blocking oxide. The miniaturization of the devices for the higher density EEPROM and their characteristics alterations accompanied with the scaling-down have been investigated. The stabler operating characteristics were attained by increasing the ratio of the channel width to length. Also, the transfer, switching, retention and degradation characteristics of the most favorable performance devices were presented and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.492-497
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• 2003

The dynamic instability for snapping phenomena has been studied by many researches. There is few paper which deal with the dynamic buckling under the load with periodic characteristics, and the behavior under periodic excitation is expected the different behavior against STEP excitation. We investigate the fundamental mechanisms of the dynamic instability when the sinusoidal shaped arch structures subjected to sinusoidal distributed excitation with pin-ends. In this study, the dynamic direct snapping of shallow arches is investigated under not only STEP load excitation but also sinusoidal harmonic excitations, applied in the up-and-down direction. The dynamic nonlinear responses are obtained by the numerical integration of the geometrically nonlinear equations of motion, and examined by the Fourier spectral analysis in order to get the frequency-dependent characteristics of the dynamic instability for various load levels.

• Transactions of the Korean hydrogen and new energy society
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• v.6 no.2
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• pp.85-90
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• 1995

Activation behavior, hydriding rate and disintegration were tested for hydrogen storage alloy particles fixed in an adhesive after treating with inorganic solution. Commertial adhesive as a binder was used. Chemical-treated particles showed the best characteristics for activation and a little effect of prevention the break down of the powders themselves after several repeated operations. Furthermore activation characteristics were found to show a similar trend to chemical-treated powders even in the fixed one with an adhesive, except for a slight decrease in reaction velocity.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.700-705
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• 2003

The general cooling tower is a device for making a cooling water in refrigerant condensers or industrial process heat exchangers. The present cooling tower have defects with noises, complicated structure and environmental problems. In this paper, we constituted a new water cooling system by using a evaporating latent heat in an enclosed tank, and this system is consisted of an enclosed vacuum tank and water driving ejector system. Several experimental cases were carried out for improvement methods of high vacuum pressure and water cooling characteristics. The ejector performance was tested in case of water temperature variations that flows in the ejector. Based on the vacuum pressure by water driving ejector, the water cooling characteristics were investigated for the vaporized air condensing effects.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.99-105
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• 2005

LNG Vaporizers must be smaller, more efficient, and easier to operate and maintain. Recently, the vaporizers with greatly enhanced performance as compared to conventional type, have been developed to fulfill these requirements. The vaporizing characteristic of LNG vaporizer with air as heat source has fixed ice. These characteristic has efficient down and total plant cost and installing space can be increase. On that reasons must be optimize through tube and pipes analysis and experiments with enhanced type in this study. In this study performance to the workong characteristics for air heating type vaporizer for super low temperature liquefied gas.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1990.10a
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• pp.63-67
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• 1990

Many characteristics of space charge in insulating materials which is the cause of insulation break down was measured quantita-tively. It was confirmed that injection charge of the electrode was trapped to form mainly space charge. In the present paper, collecting potential was determined by TSSP and mean depths of space distribution was investigated by measuring variation quantity of space charge under the different bias time, voltage and temperature. Experimental resuts was in good agreement with model analysis on a stedy state.