• International Journal of Fluid Machinery and Systems
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• v.9 no.2
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• pp.160-168
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• 2016

In high speed turbopumps, cavitation occurs and often causes the flow instabilities such as cavitation surge and rotating cavitation. The occurrence of these cavitation instabilities is considered to relate to dynamic characteristics of the cavitation, which are modelled using a cavitation compliance and a mass flow gain factor. Various types of cavitation such as a blade surface cavitation, a tip leakage vortex cavitation, and a backflow vortex cavitation occur at the same time in the inducer and the dynamic characteristics of each cavitation have not been clarified yet in experiments. Focusing on the blade surface cavitation as one of fundamental cavitation, we investigated the dynamic characteristics of the blade surface cavitation on a flat plate hydrofoil in experiments in the present study.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.3
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• pp.604-608
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• 2010

An electric fan for cooling high density electronic devices is limited and operated in very low efficiency. The corona discharge is utilized as the driving mechanism for an ionic gas pump, which allows for air flow control and generation with low noise and no moving parts. These ideal characteristics of ionic pump give rise to variety applications. However, all of these applications would benefit from maximizing the flow velocities and yields of the ionic pump. In this study, a needle-mesh type ionic pump has been investigated by focusing on the radius of curvature of corona needle points elevating the ionic wind velocity and efficiency. It is found that the radius of curvature of the corona discharge needle point influences significantly to produce the ionic wind and efficiency. As a result, an elevated ionic wind velocity and increased ionic wind generation yield can be obtained by optimized the radius of curvature of the corona needle electrode.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2023-2026
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• 2008

Cooling technologies using natural and forced convection are limited and operated in very low efficiency. The corona discharge is utilized as the driving mechanism for an ionic pump, which allows for air flow control and generation with low noise and no moving parts. These ideal characteristics of ionic pump give rise to variety applications. However, all of these applications would benefit from maximizing the flow velocities and efficiencies of the pumps. In this study a needle-mesh type ionic pump, with a ring type third electrode installed just near the needle point, has been investigated by focusing on elevating the ionic wind velocity and efficiency. As a result, the enhanced ionic wind velocity and increased power yield can be obtained with the proposed ionic pump with the third electrode.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.46-52
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present study was 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 33 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.287-293
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• 2005

In the present study, to determine the flow rate of droplets supplied to heat transfer surface after (j-1)th rebound, $D_X[j{\ge}2]^{\ast}$, it was assumed that the rebound droplets are distributed according to the Gaussian distribution from 0 to L, in which the flight distance L is determined by maximum flight distance $L_{max}$. We also assumed that $L_{max}$ is dependent on the air flow velocity and mean size of droplets. The local heat flux of a dilute spray in high temperature region was predicted using the newly evaluated $D_X[j{\ge}2]^{\ast}$. In addition, the predicted results by the present model were compared with the existing experimental data.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.166-170
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present studywas 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 34 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.9
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• pp.1594-1598
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• 2008

The ionic air pump can be used towards the thermal management of micro-electronic devices, since the size of pump can be reduced to micrometer orders. In addition, an air pump allows air flow control and generation with low noise and no moving parts. These ideal characteristics of the pump give rise to variety applications. However, all of these applications would benefit from maximizing the flow velocities of the pumps. In this study a surface discharge type air pump, with a third electrode, has been investigated by focusing on elevating the wind velocity and efficiency. As a result, the enhanced ionic wind velocity could be obtained with the third electrode of the proposed air pump.

• Proceedings of the KIEE Conference
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• 2002.11b
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• pp.280-282
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• 2002

As EG(Embedded Generation : photo-voltaic, wind, combined heat and power, fuel cell, small hydro etc.) grows fast in adopting to peak load reducing at the middle or the end of distribution system, there much has been interested in interconnection of EG. This paper discusses the various issue of a embedded generator to power system and shows the simulation of its various situation that could happen (focusing on load-flow by EG) by using a commercial software CYME(PSAF) for load-flow. With a result of above simulation, this paper shows a way of possible solution briefly.

• Journal of the Korean Society of Visualization
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• v.7 no.2
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• pp.56-63
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• 2010

In this work, a dielectrophoresis-based particle-separation device is developed which is to be used to continuously separate particles in microchannels. We fabricated the particle-separation device with combining the benefits of electrode-based DEP and insulator-based DEP. The DEP forces are generated by an array of electrodes located in both sidewalls of a main channel. According to the magnitude and frequency of electrical signals, particles with different dielectric properties experience different DEP forces, and therefore, continuously move along different streamlines in the main flow channel without need of pre-focusing process. Based on this mechanism, we examined the performance of the device by controlling the trajectory of polystyrene particles. This device is applicable to the investigation of dielectric properties of biological cells as well as the continuous separation of biological cells.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.183-189
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• 2005

A modeling of a hydraulic-gun-aerator is proposed to set up a design procedure for such devices. The aerators are used to destroy any thermal stratification that are responsible for the degradation of water qualify of lakes. The aerator produces ascending flow by using air bubbies released instantly near the bottom of the lake into a cylindrical pipe installed vertically. Differently form the diffuser-aerators, they can pull up the cold, oxygen depleted water directly to the region of the free surface, and they are believed to work effectively especially for relatively deeper lakes. Their design procedure has not been established yet though, and we propose a model focusing on the exit flow velocity at the top of the aerator through the examination of presently operating devices.