• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2648-2653
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• 2007

Recently, increasing demand on not only lighter but also extremely mobile battery make micro fuel cell device very attractive alternative. By reducing the size of fuel cell, surface tension becomes dominant factor with minor gravitational effect. Therefore, it is very difficult to detach the $CO_2$ bubble generating on a cathode side in ${\mu}DMFC$ (micro direct methanol fuel cell). The degassing of a $CO_2$ bubble has drawn quite attention especially for ${\mu}DMFC$ due to its considerable effect on overall machine performance. Our attention has been paid to the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We use Level Contour Reconstruction Method (LCRM) which is simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Journal of Energy Engineering
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• v.20 no.1
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• pp.30-35
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• 2011

To clarify the hydraulic and thermal characteristics of ice slurry which made from 6.5% ethylene glycol-water solution flow in the double tube and plate type heat exchanger, experimental studies were performed. The mass flux and ice fraction of ice slurry were varied from 800 to 3500 kg/$m^2s$(or 7 to 17 kg/min) and from 0 to 25%, respectively. Through the experiment, it was found that the measured pressure drop and heat transfer rate increase with the mass flux and ice fraction; however the effect of ice fraction appears not to be significant at high mass flux region. At the region of low mass flux, a sharp increase in the pressure drop and heat transfer rate were observed depends on mass flux.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1859-1863
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• 2007

A new type of a fretting wear tester has been designed and developed in order to simulate the actual vibration behavior of a nuclear fuel rod for springs/dimples in room temperature. When considering the actual contact condition between fuel rod and spring/dimple, if fretting wear progress due to the flow-induced vibration (FIV) under a specific normal load exerted on the fuel rod by the elastic deformation of the spring, the contacting force between the fuel rod and dimple that were located in the opposite side should be decreased. Consequently, the evaluation of developed spacer grids against fretting wear damage should be performed with the results of a cell unit experiments because the contacting force is one of the most important variables that influence to the fretting wear mechanism. Therefore, it is necessary to develop a new type of fretting test rig in order to simulate the actual contact condition. In this paper, the development procedure of a new fretting wear tester and its performance were discussed in detail.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.2
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• pp.94-100
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• 2007

An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with a modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures and large-scale instability waves.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.6
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• pp.491-499
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• 2007

The variation of a load characteristic in the motor drive is one of the most important consideration. Because the current flowing into the motor generally varies according to the load variation, it needs to design the motor drive circuit properly in accordance with the load variation. However, the load variation of the drum washing machine is irregular and large due to the water flow and reverse load torque. Therefore, to design the motor drive circuit considering this load pattern, simulation results shows the load pattern modeling of the drum washing machine based on the physical analysis in this paper.

• Proceedings of the KIEE Conference
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• 2005.11b
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• pp.347-349
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• 2005

This paper presents an efficient algorithm to estimate the maximum load level for heavily loaded power systems with the load-generation variation vector obtained by ELD (Economic Load Dispatch) and/or short term load forecasting while utilizing the elliptic pattern of the P-e curve. It is well known the power flow equation in the rectangular coordinate is fully quadratic. However, the coupling between e and f makes it difficult to take advantage of this quadratic characteristic. In this paper, a simple technique is proposed to reflect the e-f coupling effects on the estimation of maximum loadability with theoretical analysis. An efficient estimation algorithm has been developed with the use of the elliptic properties of the P-e curve. The proposed algorithm is tested on IEEE 14 bus system, New England 39 bus system and IEEE 118 bus system, which shows that the maximum load level can be efficiently estimated with remarkable improvement in accuracy.

• The Research Journal of the Costume Culture
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• v.18 no.3
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• pp.514-525
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• 2010

In the rapidly changed 21st century when the flow speed of information is so fast and the quantity of information is too much increasing, personal appearance and characteristic image-formation is highly evaluated. Nowadays personal appearance is very essential to competition and may be considered the non-linguistic expression of self-image. The beauty action of the youth is shown to follow the object which youth want to rely on or long for and it is affected by the influence of the sociocultural elements. The purpose of this study is to identify the corelation between appearance and beauty action according to the sociocultural elements of the juveniles concerning appearance and to make an inquiry into how they pursue beauty in the restrictive bound compared with the adults. As their restrictive beauty action, the practical reflection percentage of hair-style, management of face, hand and nail control will be investigated and analyzed. Furthermore this basic material of this survey was used for the development of beauty article, cosmetics and education program. With the findings of the beauty articles in which the growing generation have a deep interest, this study provided the basic materials to the customer analysis and also the reference materials to the beauty marketing.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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• pp.50-55
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• 2012

The important problem in high speed spindle is to reduce and minimize the thermal effect by motor and bearing. This paper presents the thermal characteristic analysis for a high speed spindle with and without cooling at the rear part, considering the viscosity and the flow rate of cooling oil. A high speed spindle is composed of angular contact ceramic ball bearings, high speed built-in motor, oil jacket cooling and so on. The thermal analyses of high speed spindle need to minimize the thermal effect and maximize the cooling effect and they are carried out under the various cooling conditions. Heat generations of the bearing and the high speed motor are estimated from the theoretical and experimental data. This result can be applied to the design and manufacture of a high speed motor spindle.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.755-758
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• 2002

The physical phenomena of rectangular open cavity are numerically investigated in this paper Two-dimensional cavity problems with laminar boundary layers in upstream are simulated by using the compressible Wavier-Stokes equations. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Cross-correlation is used to analyze the characteristics of wave propagation along time and spatial. Sudden phase shifting of 90 degrees is appeared near downstream edge, and this is coincident with the phase lag suggested in original Rossiter's equation. The results give a further understanding of the physical phenomenon of noise generation, and the resonance of flow and acoustic in cavity. Moreover, modified Rossiter's equation, which is more accurate and can be applied in various conditions, is suggested. The distance from the point of vortex generation to the point of vortex collapsing acts as effective distance of cavity resonance, and the phase difference between the point of vortex collapsing and the point of acoustic source acts as phase lag. The mechanism of acoustic generation is fully understood in this paper. The mechanism of acoustic generation is fully understood in this paper.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.76-79
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• 2007

From the previous researches about flow characteristic of micro-nozzle， we found that viscosity and back pressure induced heavy losses in micro nozzle. To overcome thess losses, we began to study new conceptual micro propulsion system that is thermal transpiration based micro propulsion system. It has no moving parts and can pump the gaseous propellant by temperature gradient only (cold to hot). Most of previous research on thermal transpiration is in its early stage and mainly studied for application to small vacuum facility or gas chromatography in ambient condition using nanoporous material like aerogel. In this study, we focus on basic research of propulsion system based on thermal transpiration using polyimide material in vacuum conditions.