• 설비공학논문집
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• 제20권7호
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• pp.478-485
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• 2008

The extreme steam temperature deviation experienced in the superheater of a tangentially fired boiler can seriously affect its economic and safe operation. This temperature deviation is one of the main causes of boiler tube failures. The steam temperature deviation is mainly due to the thermal load deviation in the lateral direction of the superheater. The thermal load deviation consists of several causes. One of the causes is the non-uniform heat flow distribution of burnt gas on the superheater tube system. This distribution is very difficult to measure in situ using direct experimental techniques. So, we need thermal load model to estimate the tube temperature. In this paper, we propose a thermal load distribution model by using CFD analysis and plant data. We successfully predict the tube temperature and the steam flow rate in a final superheater system from the thermal load model and one dimensional heat-flow system analysis. The proposed model and analysis method would be valuable in preventing the frequent tube failure of the final superheater tubes.

• 소성∙가공
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• 제23권5호
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• pp.317-322
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• 2014

Bursting during tube hydroforming is preceded by localized necking. The retardation of the initiation of necking is a means to enhance hydroformability. Since high strain gradients occur at the necking sites, a decrease in local strain gradients is an effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restricted in order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible to determine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, an incompressible material(such as lead) is attached to the tube where the strain-concentrated zone would contact the die. Due to the incompressibility of lead, the tube expansion is locally restricted, and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, the lead is removed from the tube, and the hydroforming continues to the final targeted shape without any local restriction. This method was successfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming fabrication.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.649-658
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• 1997

강관에 콘크리트를 충전하는 경우, 콘크리트 충전강관 기둥은 뛰어난 내력과 변형성능을 발휘한다. 그리고 콘크리트의 축열효과에 의해서 일정시간은 내화피복 없이도 내력을 유지할 수 있다. 화재발생동안 콘크리트 충전강관 기둥의 거동을 알아보고자 강관과 콘크리트의 온도에 따른 특성치 변화를 가정하고 온도 해석 및 축력-모멘트관계에 대한 수치해석을 수행하여 시간변화에 따른 변수별로 비교평가하였다. 온도에 따른 특성치는 기존문헌의 데이터를 이용하였으며 온도해석은 범용 해석프로그램인 ANSYS로 유한요소해석을 하였고 이를 바탕으로 내력에 대한 수치해석을 수행하였다.

• 대한수의학회지
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• 제36권1호
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• pp.75-82
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• 1996

Erythrocyte sedimentation rate is influenced by plasma protein, red cell itself and physiological conditions and it is clear that the measurement of erythrocyte sedimentation rate varies with technique and various environmental factors. The effect of temperature, angle of test tube, and osmobility with different percent of NaCl solution on erythrocyte sedimentation rate on sheep was determined by modified Westergren method. In sheep, as the angle of Westergren tube was decreased from $90^{\circ}$ to $45^{\circ}$, erythrocyte sedimentation rate was increased in both diluted plasma and NaCl solutions. As temperature was increased from $4^{\circ}C$ to $20^{\circ}C$ at $45^{\circ}$ angle. erythrocyte sedimentation rate was increased. In ruminants, this modified Westergren methods, erythrocyte 1 : plasma 9 instead of erythrocyte 4 : plasma 6(whole blood), enable them to have meanings as dog therefor, using this method, clinical can determine the erythrocyte sedimentation rate of ruminants for diagnosis. Because erythrocyte sedimentation rate was changed according to the angle of Westergren tube, temperature as erythrocyte diluted with NaCl, this study detected that the change of temperature, the angle of Westergren tube could change erythrocyte sedimentation rate by effecting red cell itself. The increase of osmobility owing to change of NaCl percent resulted in the decrease of rapid erythrocyte sedimentation rate. So this fact indicate that deformibility and the change of red cell volume have meaning in the change of erythrocyte sedimentation rate.

• 대한기계학회논문집B
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• 제21권1호
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• pp.185-194
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• 1997

An experimental study has been performed on the effect of baffle parameters on shell -side heat transfer in a conventional shell-and-tube heat exchanger. The baffle spacing distance and the number of baffle were varied to investigate the behavior of unequal baffle spacing correction factor which is appeared in the Bell Delaware method for prediction of the shell-side heat transfer coefficient. It was obvious that heat duties obtained from the experiment significantly deviated from those calculated by the conventional Bell-Delaware method. A new correlation of the unequal baffle spacing correction factor was developed. It was shown that the new correlation improves the accuracy of the Bell-Delaware method considerably. This result may induce the use of the Bell-Delaware method in developing a computer software for design of shell-and-tube heat exchangers.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.122-125
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• 2003

We describe a new method to initialize the raster and convergence of a flat intelligent tracking (F!T) tube. By splitting up the initialization algorithm into three parts, it can comply with the variety of boundary conditions that are stated for a consumer product. Experiments on raster initialization have shown that the new algorithm speeds up the initialization by one order of magnitude.

• 에너지공학
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• 제24권4호
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• pp.211-216
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• 2015

배열회수 보일러의 전열관군은 외부에 고온의 배기가스가 흐르면서 유동 유발 진동을 야기 시키며 배열회수 보일러의 전열관군에서 파손을 야기할 수 있어서 열교환기의 구조적 안정성을 위해 열교환기의 전열관군에서 유동 유발 진동 특성을 규명할 필요가 있다. 일반적인 열교환기 전열관군에서 유동 유발 진동에 관한 실험적 연구는 기존에 많이 진행되어 오고 있으며 단일 원관이나 전열관군의 원관들에서 유동 유발 진동에 대한 무차원 PSD(Power Spectral Density) 함수를 무차원 주파수인 Strouhal 수, fD/U의 함수로 도출된 실험적 결과들이 도출되어 있다. 본 연구는 배열회수 보일러에 사용하는 휜튜브 전열관군에서 유동 유발 진동 특성을 규명하는 것을 목적으로 한다. 이러한 것을 위해 단일 휜튜브 원관에서 비정상 상태 유동해석을 수행하여 주기적인 와동 발생 특성과 휜튜브 원관에서의 양력 변화 특성을 살펴보았다. 또한 휜튜브 원관에서 양력 변동 특성으로부터 유동 유발 진동에 따른 PSD 특성 결과를 도출하여 기존에 단순 원관에서 이루어졌던 연구들과 비교를 통해 휜튜브 원관 주위의 PSD 특성을 정립하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.102-105
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• 2001

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum suing back was found by simultaneously taking account of suing back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 추계학술발표대회 개요집
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• pp.73-75
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• 2004

The purpose of this study is to optimize Nd:YAG laser welding parameters to seaz a Rf source into a Ti micro capsule. Ti tube ends can be sealed as some length of ぉbe end is melted and coalesced. The exact control of the melted length is the most important to get sound sealing. The Nozzle type, tube rotating speed, tilt angle, focal position, pumping voltage, pulse frequency and pulse width were selected as the Nd:YAG laser welding Parameters. These Parameters were optimized by the Taguchi experimental method using 115 orthogonal array. Appearance and cross section of the seated tube ends were examined by SEM.

• 대한전자공학회논문지
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• 제25권8호
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• pp.959-965
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• 1988

Zinc diffusion characteristics and its applicabilities have been studied using an open-tube system. Thermal decomposition of arsenide(As) at gallium arsenide(GaAs) wafer surface was well inhibited by using Ga: poly-GaAs: Zn compositon as a diffusion source. Junction depth was obtained as 4.6x10**7\ulcorner exp)-1.25/kT) where activation energy of diffusion was 1.25eV. From Boltzmann-matano analysis, it could be identified that concentration dependencies of Zn diffusivity well consisted with those of kick-out model. The ideality factor of p+-n junction formed by Zn diffusion was about 1.6 and infrared light intensity was linearly varied in the range of sixty folds. It is concluded frodm these results that Zn diffuses according to kick-out model, and open-tube method is applicable to compound semiconductor devices.