• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.79-92
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• 1998

A numerical study has been performed to obtain the air-side flow and heat transfer characteristics for a two-row lanced finned tube heat exchanger with 7 mm tube outer diameter. The increases of dimensionless local heat flux at the leading edge of slit and bottom surface of the fin were noticed. The temperature of air at downstream of the 2nd row of the lanced fin becomes more uniform than that of the plain fin because the mixing of energy increases by the slit and the side-slit. As the inlet velocity increases, the contribution of the 1st row to heat transfer decreases and that of 2nd row increases.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.3
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• pp.54-60
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• 2013

Numerical analysis of the radiant heat characteristic around heatsink according to arrangement and shape of fin on 60W-LED lamp is conducted in this study. In the case of top blow blowing from upper side on LED lamp, there is just little difference in cooling characteristics according to the height of fin. On the other hand, the fin arranged side by side has the advantage of heat transfer enhancement by comparing with zig-zag type because it leads to more loss of flow. In case of making fin round to increase the amount of heat transfer, designing arrangement with the minimized loss of flow has the advantage of characteristic.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.289-292
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• 2008

Highly over-expanded nozzle of the rocket engines will be excited by non-axial forces due to flow separation at sea level operations. Since rocket engines are designed to produce axial thrust to power the vehicle, non-axial static and/or dynamic forces are not desirable. Several engine failures were attributed to the side loads. Present work investigate the unsteady flow in an over-expanded rocket nozzle in order to estimate side load during a shutdown/starting. Numerical computations has been carried out with density based solver on multi-block structured grid. Present solver is explicit in time and unsteady time step is calculated using dual time step approach. AUSMDV is considered as a numerical scheme for the flux calculations. One equation Spalart-Allmaras turbulence model is selected. Results presented here is for two nozzle pressure ratio i.e. 100 and 20. At 100 NPR, restricted shock separation (RSS) pattern is observed while, 20 NPR shows free shock separation (FSS) pattern. Side load is observed during the transition of separation pattern at different NPR.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.181-189
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• 1985

The effect of the Coriolis force on the 2-D turbulent boundary layer which is developed in the side wall of the rotating rectangular flow channel was investigated. In this study, we measured mean velocities, turbulent velocity components(axial as well as lateral ones) and Reynolds stresses of the turbulent boundary layer. For high Reynolds number flows, the turbulent boundary layer without pressure gradient is hardly affected by the rotation. For low Reynolds number flows, however, the shearing stress at suction side decreases. Consequently, the velocity near the wall become slower so that the thickness of the viscous sublayer expands. On the other hand, the velocity near the wall at pressure side turns out increased.

• Journal of Power Electronics
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• v.16 no.2
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• pp.399-413
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• 2016

This paper presents a topology for a modular power electronic transformer (PET) and a control scheme. The proposed PET consists of a cascaded H-Bridge rectifier on the primary side, a high-frequency DC/DC conversion cell in the center, and a cascaded H-Bridge inverter on the secondary side. It is practical to use PETs in power systems to reduce the cost, weight and size. A detailed analysis of the structure is carried out by using equivalent circuit. An algorithm to control the voltages of each capacitor and to maintain the power flow in the PET is established. The merits are analyzed and verified in theory, including the bi-directional power flow, variable voltage/frequency and high power factor on the primary side. The experimental results validated the propose structure and algorithm.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.485-492
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• 2002

Heat transfer and pressure drop on the air side of a plate-louvered fin heat exchanger with new shape of louver fin have been investigated experimentally. Water is employed inside the flat tube to transfer heat with air for convenience. This problem is of particular interest in the design of a plate-louvered heat exchanger. The effect of air flow rate, water flow rate and water temperature on pressure drop as well as heat transfer in air side are studied in detail. The present results showed a good agreement qualitatively with the previous results in general. Based on the experimental data, f-factor and j -factor correlations of the present louvered-fin are suggested. It is also found that heat transfer could be enhanced with new shape of louver fin, compared with the conventional louvered-fin, while the f-factor remains unchanged.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.110-119
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• 1994

Three dimensional characteristics of fluid flow and heat transfer have been studied numerically around the latent heat storage vessel which was applied to the practical ice-storage system. The result obtained indicates that the value of frictional coefficient decreases with decrease of baffle width. For the baffle spacing. $S/H_D=9.375$, baffle height. $H/H_D=0.5$ and various pressure drop, average Nusselt numbers in heat transfer surface are much dependent on the width of side baffle and middle baffle. that is. Nu_m decreases with decrease of the width of middle baffle when the width of side baffle is 4.375, where as the optimum condition of side baffle for $Nu_m$ exists in the range of 3.5< $B_1/H_D$ <4.375 at the width of middle baffle, $B_2/H_D=6.875$.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.97-106
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• 2019

This study was conducted to propose a reasonable requirement regulation of barrier system of rubble mound revetment offshore landfill for preventing contaminant leakage. The barrier is composed with bottom layer and side barrier. The bottom layer was assumed as impermeable clay layer and side barrier was composed with HDPE sheet (primary element) and mid-protection layer (supplementary element). Seepage-advection-dispersion numerical analysis has been conducted using SEEP/W and CTRAN/W programs under steady flow. As the results, the minimum required barrier regulations for hydraulic conductivity and thickness of the bottom layer were suggested. For side barrier, the extended length of HDPE sheet and the hydraulic conductivity of mid-protection layer were also suggested.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.335-338
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• 2007

In the case of an antiaircraft missile, high angle of attack flight capability is required to get the agile maneuverability in a supersonic flow. Even through a symmetric slender body does not have side slip, asymmetric vortex is generated at high angle of attack conditions. This asymmetric vortex produces unnecessary side force and yawing moment; hence, these effects deteriorate directional stability. In this study, the numerical analysis of asymmetric vortices around the slender body was conducted at high angle of attack supersonic flow. In order to simulate the vortices, a bump is installed on the nose of the slender body. As a result of the numerical analysis, the asymmetric vortices around the slender body could be simulated.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.549-554
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• 2003

EPRI PPM (Performance Prediction Methodology), a method used for the prediction of required thrust of valves, can not be applied to unbalanced-disk globe valves operated in the fluid when the fluid temperature is above $150^{\circ}F$ because the thrust increase caused by the friction between the valve disk and body is not considered in the PPM. In order to apply PPM to the valves, EPRI suggested new friction prediction method to be added in the code. This paper analyzes the applicability of the prediction method comparing the disk-to-body friction load predicted from the method with the measured friction load from the field tests. The maximum values from the prediction method and those obtained from the test were 268lbs and about 1500lbs, respectively. It is included that the prediction method should be improved for the realistic prediction of disk-to-body friction load.