• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.183-188
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• 2012

This study was carried out to design the spray nozzle tip for airless spray coating. Airless spray coating is the process of coating an object with a liquid spray of paint or other fluid. The nozzle tip controls the fluid flow rate and creates back pressure in the system. The nozzle tip also defines the spray pattern by the size and shape of the orifice. The spray pattern of nozzle tip was investigated numerically using ANSYS CFX ver. 14.0. It was observed that performance result of designed nozzle tip was correspond well, compared with that of GARCO nozzle tip.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.12
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• pp.682-690
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• 2002

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval.. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 7㎾, 30KHz experimental prototype.

• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.121-124
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• 2002

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due In this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer The proposed ZVZCS converter is verified on a 7kW, 30kHz experimental prototype.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.689-693
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• 2001

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 10 kW, 30kHz experimental prototype.

• Korean Journal of Remote Sensing
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• v.22 no.5
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• pp.415-419
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• 2006

X-SAR images taken on the coastal waters of Hwanghe province in Korea during SIR-C/X-SAR campaign in April and October 1994 are analysed. The SAR images show the peculiar signatures like nail marks, curved long string, and vortex street patterns and they all seem to be produced by strong interactions between the topography in the coastal waters and tidal currents. The nail mark signatures are located at the same position of small scaled sand banks and the curved line patterns are almost identical to the outer boundary of large sand banks. Based on the tidal records, all the three images are taken at the almost same phase of tidal cycles, which are close to the low tide. It seems that bottom shapes are more strongly appeared on the SAR images when the tidal currents are slow. The front between two different current velocities caused by the flows along the steep boundaries of sandbanks is also the main factors imprinting the bottom features to the sea surface SAR images.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.98-98
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• 2022

도수는 사류가 상류로 천이되며 흐름이 불연속적으로 변하는 현상이다. 도수는 롤러와 벽 제트와 같은 흐름이 발생하는 영역으로 구분되며 큰 에너지 손실을 발생시키므로, 보나 댐과 같은 수리시설물에서는 에너지 소산을 위한 목적으로 도수를 발생시킬 수 있다. 도수구간 중 롤러 영역에서는 공기가 유입되어 복잡한 3차원 2상 흐름을 발생시키므로 공기방울의 거동에 대한 정밀한 모의는 매우 중요한 것으로 평가된다. 그러나 현실적으로 롤러 영역에서의 작은 공기방울까지 재현하는 것은 어려운 일이다. 본 연구에서는 k-ω SST 난류모형을 이용하여 수문 아래에서 발생하는 자유도수를 수치모의하고 연행된 공기량에 대한 특성을 검토하였다. 롤러 영역에서 격자의 해상도를 다르게 하여 도수구간 내 공기의 체적비와 공기방울의 크기 및 공기방울의 거동을 분석하였다. 실내 실험자료에 난류모형을 적용하고 그 결과와 비교하여 모의 결과의 적정성을 확인하였다. 또한 도수구간에서 공기방울 거동의 정밀한 모의가 평균흐름 및 난류량의 종방향 변화에 미치는 영향을 검토하였다.

• Journal of ILASS-Korea
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• v.6 no.1
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• pp.18-24
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• 2001

Liquid fossil fuel contaminated by water can cause trouble in the combustion processes and affect the endurance of a combustion system. Using an optical sensor to monitor the water content instantaneously in a fuel pipeline is an effective means of controlling the fuel quality in a combustion system. In two component liquid flows of oil and water, the flow pattern and characteristics of water droplets are changed with various flow conditions. Additionally, the light scattering of the optical sensor measuring the water content is also dependent on the flow patterns and droplet characteristics. Therefore, it is important to investigate the detailed behavior of water droplets in the pipeline of the fuel transportation system. In this study, the flow patterns and characteristics of water droplets in the turbulent pipe flow of two component liquids of gasoline and water were investigated using optical measurements. The dispersion of water droplets in the gasoline flow was visualized, and the size and velocity distributions of water droplets were simultaneously measured by the phase Doppler technique. The Reynolds number of the gasoline pipe flow varied in the range of $4{\times}10^{4}\;to\;1{\times}10^{3}$, and the water content varied in the range of 50 ppm to 300 ppm. The water droplets were spherical and dispersed homogeneously in all variables of this experiment. The velocity of water droplets was not dependent on the droplet size and the mean velocity of droplets was equal to that of the gasoline flow. The mean diameter of water droplets decreased and the number density increased with the Reynolds number of the gasoline flow.

• Tribology and Lubricants
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• v.30 no.6
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• Textile Coloration and Finishing
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• v.20 no.6
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• pp.82-86
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• 2008

Cooling function is definitely one of the most desirable attribute of clothing. In spite of the recent progress on phase changing material(PCM) research, the final products with sufficient amount of cooling capability have not yet to be developed in market. A new concept of cooling fabrics has been proposed by applying "Peltier effect" to textile materials. It occurs whenever electrical current flows through two dissimilar conductors; depending on the direction of current flow, the junction of the two conductors is absorbed or released heat. This effect has been tested on P-type and N-type conducting polymers. A P-type conductive polypyrrole coated fabric was synthesized by in-situ polymerization on plain weave PET to make conductive fabrics. And an N-type electrically conductive material was synthesized by treatment of MWNT and polyethyleneimine(PEI). A noticeable amount of temperature difference has been found on the fabrics.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.847-852
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• 2009

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damange, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle inside feed-water heater installed downstream of the turbine extraction stream line. At that point, the extract steam from the turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows to reverse direction after impinging the impingement baffle, the shell wall of feedwater heaters may be affected by flow-accelerated corrosion. In this paper, to compare wall thinning range according to change entrance nozzle diameter and position with reference numerical analysis model's wall thinning range, various numerical analysis models applied. In case of changing diameter, four different diameter is applied. And a side of nozzle position, two different position-vertical type and parallel type-is applied. And then this paper describes operation of numerical analysis which is composed similar condition with real feed water heater. In conclusion, this study shows effective design for shall wall thinning by changing nozzle diameter and position.