• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4266-4273
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• 2023

In a severe reactor accident, a crust will form on the surface of the molten material during the core melting process. The crust will have a contact melting with the internal components of the reactor. In this paper, the contact melting process of the molten material on the austenitic stainless steel plate bundles is studied. The contact melting model of parabolic molten material on the plate bundles is proposed, and the rule and main effect factors of the contact melting are analyzed. The results show that the melting velocity is proportional to the slope of the paraboloid, the heat flux and the distance between two plates D. The influence of melt gravity and the plate width on melting velocity is negligible. The thickness of the molten liquid film is proportional to the heat flux and plate width, and it is inversely proportional to the gravity. With the increase of D, the liquid film thickness decreases at first and then increases gradually. The liquid film thickness has a minimum against D. When the width of the plate is small, the width of the plate is the main factor affecting the thickness of the liquid film. The parameters are coupled with each other. In a severe reactor accident, the wider internal components of reactor, which can increase the thickness of the melting liquid film and reduce the net input heat flux from the molten material to the components, are the effective measures to delay the melting process.

• 설비공학논문집
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• 제2권4호
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• pp.295-302
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• 1990

The purpose of this study is augmentation of heat transfer without additional power in two-dimensional impinging air jet. The technique of heat transfer augmentation used in this experiment is to place rod bundles in front of the flat heated surface. The effects of rod diameter, nozzle-to-target plate distance and the nozzle exit velocity on heat transfer have been investigated. The main conclusions obtained from this experiment are as follows. High heat transfer augmentation is achieved by means of flow acceleration and thinning of boundary layer by placing rod bundles in front of the flat plate. Average heat transfer coefficient becomes maximum in the case of H/B=10,D=4mm. For H/B=2,D=4mm, maximum heat transfer augmentation has been determined to be about 1.5 times larger than that of the flat plate. Heat transfer augmentation by placing the rod bundles at 12m/s is to be about 2 times more than increasing nozzle exit velocity from 12m/s to 18m/s.

• 전기학회논문지
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• 제56권10호
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• pp.1791-1795
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• 2007

Small ions generated at conductor corona sources remain in the atmosphere until they recombine with ions of opposite polarity, attach to aerosols, or make contact with an object. Ion current density is major factor to design conductor configuration of DC overhead transmission line. Several techniques have been used to measure the ion current of HVDC overhead transmission line. In this study, the ion current density was measured by a plate electrode made of a metal flat board at DC corona cage. The sensitivity of the plate electrode is $0.156uA/m^2/V$. To obtain an useful database on corona discharge, it is necessary to do corona test on several kinds of conductor bundles. Therefore, a number of experiments were conducted on several kinds of conductor bundles. To reliably analyze ion effects, corona cage test data were obtained over a long period of time under various weather conditions and expressed as a statistical distribution. Ion current density distribution in foul weather shows a significant increase in levels over the corresponding fair weather. Based on this results, we evaluated the environmental characteristic caused by ion flow of three candidated conductor bundles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1046-1051
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• 2004

A plate-fin-tube heat exchanger used for a $SF_{6}$ gas-insulated transformer is extremely important since the dissipation of the heat generated from inside coils has a significant effect on the performance as well as the durability of the transformer. The heat exchanger consists of corrugated plate fins and staggered array tube bundles for coolant. In order to find out heat transfer and pressure drop characteristics, series of numerical analyses for plate fins with enhanced surface geometries were conducted. Based on the results of the numerical analyses, an improved model of the plate fin has been proposed.

• 설비공학논문집
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• 제1권2호
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• pp.182-189
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• 1989

The propose of this study is augmentation of heat transfer without additional external power in 2-dimensional impinging air jet. The passive heat transfer augmentation method tried in this experimental study is placement of rod bundles with the clearance, 2mm, in front of the heat transfer surface. The effects of pitch distance among rods and nozzle-to-target plate distance are investigated. The overall heat transfer rate of flat plate with rods reaches maximum at H/B=10 and P=40mm, and for H/B=2 and P=40mm the augmentation rate of heat transfer becomes maximum to a value which is about 1.57 times that of the flat plate without rods.

• 설비공학논문집
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• 제4권1호
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• pp.48-56
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• 1992

The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular air jet impinging vertically on the flat heating surface. In an attempt to enhance the heat transfer rate in two-dimensional impinging jet, the technique used in the present study was placement of square rod bundles as a turbluence promoter in front of the heat transfer surface. The effects of the clearance between the flat plate and square rod, and the nozzle exit velocity on the heat transfer characteristics have been investigated experimentally. The results obtained through this study were summerized as follows. High heat transfer enhancement was achived by means of flow acceleration and thinning of boundary layer by inserting rods in front of the heating flat plate. The smaller the clearance between rod and heating plate was, the larger heat transfer effect became. Average Nusselt number reached maximum at $Re=5.76{\times}10^4$ and C＝1㎜ and the enhancement rate of heat transfer became maxium at this condition with the enhancement ratio as high as about 1.427 when normalized by the flat plate value. The correlating equation of average Nusselt number and Reynolds number was obtained, which is $\bar{N}uo=1.324{\cdot}Re^{0.459}{\cdot}(C/A)^{-0.034}$.

• 한국전산유체공학회지
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• 제21권4호
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• pp.28-32
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• 2016

In the previous study, it is proved by numerical simulation that the baffle shaped as the porous plate installed in the inlet chambers improves the redistribution of the flow injecting to the tube bundles. In the present study, numerical simulation has been performed to investigate the effects of the flow distributors on the thermal characteristics of the shell and tube heat exchangers. The flow fields have been analysed by the three-dimensional Navier-Stokes solvers including the thermal conditions on the shell sides. The numerical results showed that the presence of the baffles improves the redistribution of the heat transfer to the tube bundles though the overall performance drop slightly on the present flow conditions.

• 대한기계학회논문집B
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• 제39권3호
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• pp.223-229
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• 2015

배플과 관군간의 누설유동이 쉘-관 열교환기 성능에 미치는 영향을 FLUENT 를 사용하여 조사하였다. 쉘측 출구온도를 최대로 하는 최적누설유동을 찾기 위해 쉘측 단면적에 대한 누설단면적 비가 0%-40% 범위의 5 가지 누설유동을 가진 쉘-관 열교환기에 대하여 CFD 모델이 개발되었다. 관 입구 및 벽면온도를 일정하게 유지하고 Reynolds 수를 4952 부터 14858 증가시키면서 유동장 및 온도장을 계산하였다. 해석결과, 출구온도, 압력강하, 열전달률은 Reynolds 수뿐만 아니라 누설유동에도 크게 영향을 받는 것으로 나타났다. 누설유동은 열전달률과 압력강하를 동시에 낮추는 결과를 제시한 기존의 결과와는 달리, 본 연구에서는 적정의 누설유동은 배플 주위의 재순환영역에 추가적인 모멘텀을 공급함으로써 최대출구온도, 작은 압력강하, 높은 열전달률을 유도하는 효과를 발휘하는 새로운 결과를 얻었다. 20%의 누설단면적이 최적의 누설단면적으로 나타났다.

• 태양에너지
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• 제13권1호
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• pp.11-21
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• 1993

이차원(二次元) 충돌공기분류계(衝突空氣噴流系)에서 흐름방향과 수직(垂直)이 되게 설치한 평판전열면(平板傳熱面) 전방(前方)에 난류촉진체(亂流促進體)인 정4각(正4角) 로드군(群)(로드폭=4mm, 로드피치=50mm)을 설치하고 로드와 전열면(傳熱面)사이의 간극(間隙)(C=1, 2, 4, 6mm), 노즐출구와 전열면간(傳熱面間) 거리(H/B=2, 6, 10, 14) 및 Re수($Re=6.410{\times}10^3{\sim}5.769{\times}10^4$)를 변화시켜 실험한 결과, 평판(平板)에서 열전달계수(熱傳達系數)의 감소율이 큰 영역에서도 로드를 설치하므로써 높은 열전달계수(熱傳達係數)를 얻을 수 있었으며, 실험범위내의 Re수와 H/B에 대하여 열전달계수(熱傳達係數)가 최대(最大)가 되는 최적간극(最適間隙)은 C=1mm이고, 최대(最大) 열전달증진율은 H/B=2, C=1mm에서 로드를 설치하지 않은 평판(平板)보다 약 43% 증진한다.

• 한국수정란이식학회지
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• 제19권3호
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• pp.283-289
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• 2004

동결 과정 중 필수적인 단계중 하나인 냉각(cooling)과 냉각 후 배양시간이 생쥐 난자의 방추체의 형태와 염색체의 배열에 미치는 영향을 알아봄으로서 냉각 후 손상되었던 난자의 방추체와 염색체가 정상적으로 회복하는데 필요한 최적의 배양시간을 알아보기 위해 본 실험을 실시하였다. 생후 4-6주령의 암컷 B6C3Fl 생쥐를 과배란 처리하여 metaphase II상태의 난자를 회수하여 다음과 같이 처리하였다. 대조군은 난자를 냉각처리하지 않았으며 실험군은 난자를 $0^{\circ}C$에서 30분간 냉각한 후 37$^{\circ}C$에서 가온하여 즉시 일부 난자는 면역형광 염색을 실시하고 나머지 난자는 5% $CO_2$ 37$^{\circ}C$가 유지된 배양기내에서 Ml6 배지에 각각 5분, 15분, 30분, 60분, 120분간 배양한 후 면역 형광염색을 실시하였다. 난자의 방추체와 염색체를 평가하기 위한 면역형광염색은 Zenes 등의 방법(2001)에 준하여 실시하였다. 냉각처리하지 않은 생쥐 난자를 면역형광 염색하여 방추체와 염색체를 관찰한 결과 생쥐 metaphase II 상태의 난자는 대칭성의 원통모양의 방추체 형태를 보였으며 염색체는 metaphase plate위에 분리된 다발모양으로 밀집되어 보였다. 냉각 직후 미세관의 소실에 의한 방추체 형태의 이상과 형광성의 소실이 나타났으며 염색체는 다발모양의 밀집된 형상에서 벗어나 비정상적인 배열상을 보였다. 냉각 처리된 난자를 37$^{\circ}C$에서 가온하고 배양하였을 때 미세관의 재중합이 일어나 미세관의 형광성을 회복하기 시작하였고 방추체는 정상적인 배열상으로 회복되었다. 생쥐 난자를 냉각처리한 후 배양시간에 따른 방추체 미세관의 형광성(FIS), 염색체의 배열, 방추체의 형태를 비교하였다. 배양 5분에서 60분까지 FIS, 정상 염색체 배열을 보인 난자의 비율, 정상 방추체의 형태를 보인 난자의 비율이 점진적으로 증가하였으나 120분 배양에서는 감소하였다(P<0.05). 위의 세 가지 평가를 기준으로 하여 냉각 후 난자의 회복율을 관찰하였을 때 배양 60분에서 최상의 회복율을 나타냈다.