• 대한기계학회논문집B
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• 제34권2호
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• pp.179-184
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• 2010

스트레이트 휜 히트 싱크가 장착된 공간에 팁 클리어런스(tip clearance)와 바이패스 유동이 열성능에 미치는 영향을 실험적으로 규명하고자 한다. 수평 및 수직 방향으로의 바이패스 유동에 의한 열성능 평가는 열식 질량 유량계(MFC)와 소형 풍동으로 이루어진다. 팁 클리어런스와 바이패스 유동에 의한 히트 싱크의 열성능은 열저항을 통하여 평가한다. 실험 결과, 스트레이트 휜 히트 싱크의 열저항은 팁 클리어런스가 증가함에 따라 점진적으로 증가하며, 유동 가이드 장치는 바이패스 유동을 감소하는 역할을 한다. 본 연구에서는 동일 유량 조건에서 히트 싱크의 입구에서 유동 가이드 장치까지의 거리에 따라 스트레이트 휜 히트 싱크의 최적값이 존재함을 확인하였다. 히트 싱크로 유입되는 유량이 증가함에 따라 유동 가이드 장치에 의한 열성능 개선 정도는 증가한다.

• 대한기계학회논문집B
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• 제37권7호
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• pp.709-716
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• 2013

팬 필터 유닛 (FFU)은 청정실 천정에 설치되어 정화된 공기를 공급하는 장치이다. FFU가 대형화되면서 출구면에서 속도가 불균일해지고 결과적으로 청정실에서 생산되는 제품의 품질 또는 생산성을 떨어뜨리게 된다. 이러한 문제를 해결하기 위해 가이드 베인이 설치되는데 가이드 베인은 속도를 균일하게 하지만 유동저항을 유발하여 동력이 일정하게 주어진 경우 공급되는 유량을 감소시킨다. 따라서 속도 균일성을 확보하면서 유량 감소를 최소화하는 최적설계가 요구된다. 본 연구에서는 FFU의 외벽과 중앙에 설치된 가이드 베인의 각도와 길이를 변경하면서 수치해석을 수행하여 가이드 베인의 성능 개선 방안을 도출하였다. 외벽에 설치된 가이드 베인의 경우, 형상을 변경하여 유량이 1.5% 감소하는 조건에서 속도 균일도를 3.7% 향상시킬 수 있었다. 중앙 가이드 베인의 경우 유량이 0.7% 감소하는 조건에서 속도 균일도를 2.9% 향상시킬 수 있었다.

• 설비공학논문집
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• 제21권11호
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• pp.599-605
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• 2009

This paper presents a numerical evaluation of the flow rate of air conditioner outdoor unit by investigating the effects of fan location and shroud shape. To determine optimal design parameters, we investigated the exhaust flow rate by changing shroud height, fan height, fan guide height, and fan width. The 3rd order central composite design was performed to select three most important parameters affecting the exhaust flow rate. According to the result of response surface method, the exhaust flow rate of the optimum model increased by 6.25% compared to that of the base model.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.963-970
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• 2018

The U.S. Nuclear Regulatory Commission, Regulatory Guide 1.20 needs to perform a comprehensive vibration assessment program for reactor internals during preoperational and startup testing for nuclear power plants and extended power uprate. Although the measurement program is one of the core programs, it is rarely carried out except for a first-of-a-kind or a unique design. This article describes measurement results of vibration and stress for the comprehensive vibration assessment program for an APR-1400 reactor internals. The measurement was performed at an upper guide structure during the pre-core hot functional test of Shin Kori unit 4 reactor internals because the Shin Kori unit 3 and 4 are the first construction project for the APR-1400, and the upper guide structure assembly was to design change compared with the valid prototype. We confirmed that all measured results are within the test acceptance criteria. It means that the structural integrity of the APR-1400 reactor internals was secured for the flow-induced vibration.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.453-458
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• 2009

This paper presents a numerical evaluation of the flow rate of air conditioner outdoor unit as function of shroud design parameters. To determine the optimal design parameters, we investigated the flow rate by changing bell mouth height, fan height, fan guide height, fan width. The evaluation of the relative priority of the design parameters was performed to choose three important parameters in order to use a response surface method. The flow rate of the optimum model, compared to that of the base model, was increased by about 6.25%.

• 한국항공우주학회지
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• 제32권8호
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• pp.72-81
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• 2004

초고속 지상 운행체에 대한 풍동실험을 통하여 단단한 채널과 운행체 사이에 발생하는 공력 상호작용을 연구하였다. 풍동실험시 유속은 30m/see에서, 단위길이당 레이놀즈수는 $3.1{\times}10^5/m$였다. 가변지면과 안내로와 같은 실험장치들이 이 실험을 위해 사용되었다. 운행체는 지면과 운행체 사이의 거리가 가까워질수록, 안내로 사이의 간격이 좁아질수록 양력은 급격히 증가하였고, 항력은 미세하게 감소하였으며, 키놀이 모멘트는 억제되어 정안 정성을 증대시켰다. 연선을 사용한 유동가시화를 통하여 운행체가 채널 내를 운행할 때의 유동 특성을 채널이 없는 경우와 비교하였고 공력측정 결과를 뒷받침하였다. 채널 지연과 안내로의 영향으로, 운행체 하부에서의 유동은 날개의 익단판 외부로 흐르지 못하며, 이것이 운행체 양력증가의 주요 원인이 되었다.

• 한국초등과학교육학회지:초등과학교육
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• 제35권2호
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• pp.205-215
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• 2016

This study aims to investigate how elementary teachers use teachers' guide in preparation for science lessons. First, different uses of teacher's guide were analyzed. Second, how and why teachers use each section in teacher's guide were analyzed. For the study, 24 elementary school teachers were interviewed in depth. The semi-structured in-depth interviews were conducted individually and/or in small group, and additional interviews were held when necessary. The results showed that most of the teachers used teacher's guide only substitutionally, and some teachers rarely use teacher's guide, while only 3 out of 24 teachers used teacher's guide in detail. The reasons that teachers used the teacher's guide substitutionally or rarely were that most science lessons include experiments, and science textbook itself provides enough information for preparation of science lessons for 3rd and 4th grade students. The results also revealed that only few teachers read the general guideline in teacher's guide. Some sections of teacher's guide were not used. The sections that many teachers used were the aims of lesson, the learning system of the unit, background knowledge, flow of lesson, learning contents and activities. This study specifically examined the actual use of teacher's guide for lesson preparation and discussed implications for the development of more helpful teacher's guide.

• Nuclear Engineering and Technology
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• 제40권1호
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• pp.37-48
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• 2008

Flow fields inside feeder pipes have been simulated numerically using a CFD (computational fluid dynamics) code to calculate the shear stress distribution, which is the most important factor in predicting the local regions of feeder pipes highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. The CFD approach, with schemes used in this study, to simulate the flow situations inside the CANDU feeder pipes has been verified as it showed a good agreement between the investigation results for the failed feedwater pipe at Surry unit 2 plant in the U.S. and the CFD calculation. Sensitivity studies of the three geometrical parameters, such as angle of the first and second bends, length of the first span between the grayloc hub and the first bend, and length of the second span between the first and the second bends have been performed. CFD analysis reveals that the local regions of feeder pipes of Wolsung unit 1 in Korea, on which wall thickness measurements have been performed so far, are not coincident with the worst regions predicted by the present CFD analysis located in the connection region of straight and bend pipe near the inlet part of the bend intrados. Finally, based on the results of the present CFD analysis, a guide to the selection of the weakest local positions where the measurement of wall thickness should be performed with higher priority has been provided.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.594-601
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• 1997

Propeller fans are commonly equipped in outdoor units of air-conditioners to provide effective cooling in a dried heat exchanger. A new design technique was developed to satisfy requirements of aerodynamic and aeroacoustic performance, which employs the intersection method of two cylinders for mean camber line. Three proto-types of propeller fan including Palm-Shaped, Highly-Swept(PSHS) fan (proto 3)were not only to provide low lift forces for dipole sound, but also to reduce the organized tip vortices interacting with the fan guide causing narrow-banded rotating instabilities. Cross-correlation technique was applied to study flow noise source characteristics for three proto-type fans designed. The cross-correlations between a microphone at far field and a hot-wire sensor at near field show that flows near hub region of proto 3 fan are less organized and the flow structures especially at high flow rate coefficients for proto 3 fan are less correlated with noise generated than other proto-types fans.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.289-294
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• 2002

In this study, performance, flow characteristics and noise of a cross-flow-fan system, used in indoor unit of the split-type air conditioner, were predicted by computational simulation. Triangular elements were used to mesh the calculation domain and quadrilateral elements were attached to the blade surfaces and walls to enhance the simulation quality. The unsteady incompressible Wavier-Stokes equations were solved using a sliding mesh technique on the interface between rotating fan region and the outside. Two stripes of velocity stream inside the cross-flow-fan were shown - the one was due to the eccentric vortex and the other was due to the normal entrance flow. As the flow rate increased, the center of the eccentric vortex moved toward the inner blade tip and rear-guide, and the exiting flow still had velocity variation along the stabilizer, which can increase the noise level. The acoustic pressure was calculated by using Lowson's equation. From the calculated acoustic pressure, it was found that the trailing edge is a dominant of acoustic generation.