• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.683-688
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• 1997

원전의 중대사고 발생시 형성될수 있는 노심용융물의 고화피막층을 동반하는 용융물의 자연대류 열절달 특성에 대한 실험결과를 정밀 분석하고, 이에 대한 해석적 연구를 수행하였다. 본 연구대상 실험은 종횡비가 작은 경우와 큰 경우에 대하여 용융물을 자연대류와 강제대류로서 냉각하는 조건에서 경계조건에 따른 용융물의 피막층 두께를 측정하였고, 피막층 주변의 열전달량을 측정ㆍ분석한 것이다. 실험결과를 정밀 분석한 결과, 용융물의 고화 피막층 형성이 용융물의 자연대류 열전달양에 많은 영향을 미쳤으며, 종횡비가 큰 경우는 냉각 조건도 자연대류 열전달 양에 다소 영향을 미치는 것으로 나타났다. 또한 고화층 두께 증가에 따른 종횡비 감소는 자연대류 열전달양 감소율을 작게하는 것으로 나타났다. 피막층 형성이 있는 용융물의 자연대류 열전달 해석 결과, 실험에서의 열손실 때문에 용융물의 고화 피막층 두께가 실험결과보다 다소 작게 나타났으며, 자연대류 열전달 흐름이 피막층 형성에 미치는 것으로 나타났다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.41-46
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• 1997

The change of flow field and the effects of convective heat transfer on the shape and location of melt/crystal interface has been studied during the crystal growth by the heat exchanger method. Although the thermal structure is stable in the crucible, the flow due to the natural convection driven by radial temperature gradient is significant, because the thermal stability is broken by the hemispherical melt/crystal interface shape. The maximum interface deflection with convection is smaller than without and the convective heat transfer should be considered to simulate the heat transfer process of heat exchanger method rigorously.

• Journal of Energy Engineering
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• v.23 no.2
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• pp.13-20
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• 2014

The natural convection heat transfers of a helical coil in a duct were measured experimentally varying the inclination. To achieve high Rayleigh number, mass transfer experiments instead of heat transfer experiments were performed based upon the analogy. The $Ra_D$ was fixed to $4.55{\times}10^6$. The turn numbers were 1~10. the pitch to diameter ratio were 1.3~5, and the inclination of the helical coil $0^{\circ}{\sim}90^{\circ}$. The measured $Nu_D$ for a single turn of the helical coil was very close to that from McAdams heat transfer correlation for a horizontal cylinder. The heat transfers of the helical coil were varied by the pith, number of turns, and duct height in a complex manner showing the velocity, chimney, and pre-heating effects. The results of the study contributes to the phenomenological analyses of the natural convection heat transfer of a compact heat exchanger.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.254-264
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• 2012

Rayleigh-Benard natural convection experiments were carried out as the preliminary experiment to simulate the natural convection of the core melt at the severe accident conditions. This work focused on the influences of plate separation distance(s), the existence of the side walls and crust geometries of upper and lower plates. Based upon the analogy concept, a cupric acid-copper sulfate electroplating system($H_2SO_4-CuSO_4$) was employed as the mass transfer system and measurements were made for $Ra_s$ ranging from $1.06{\times}10^7$ to $2.91{\times}10^{10}$. The test results measured for a single horizontal plate were in good agreement with the correlation reported by McAdams and those for two horizontal plates showed the similar trend to the existing Rayleigh-Benard heat transfer correlations developed by Dropkin and Somerscales, Globe and Dropkin. The measured heat transfer rate decreased with the increasing separation distance between the two plates and became similar to those for a single horizontal plate. Fin arrays mounted on both upper and lower plates enhanced the heat transfer rates. For all cases, the heat transfer rates measured for open side walls are higher than those for closed ones.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.242-251
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• 2011

The effects of top and bottom lids on the natural convection heat transfer phenomena inside vertical cylinders were investigated experimentally for $Ra_{Lw}$ from $9.26{\times}10^9$ to $7.74{\times}10^{12}$. Using the concept of analogy between heat and mass transfer, a cupric acid-copper sulfate electroplating system was employed as mass transfer experiments replacing heat transfer experiments. The natural convection heat transfer of both-open cylinders in laminar and turbulent flows was in good agreement with the existing heat transfer correlations developed for vertical plates. The effects of top and bottom lids on the heat transfer rates were very similar to the studies of Krysa et al. and Sedahmed et al. and Chung et al. With the copper lids, the bottom-closed cavity showed the highest heat transfer rates and then followed both-closed, top-closed, both-open ones in both laminar and turbulent flows. However with the acryl lids, the similar trends were observed except that the heat transfer rates for both-open were higher than top-closed one. The use of the copper lids increased the heat transfer rates compared to the acryl lids due to the hydrodynamic interaction of the flows developed for the different heated faces. This study extended the ranges of flow conditions of the existing literatures and proposed the empirical correlations.

• Journal of the KSME
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• v.29 no.4
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• pp.394-402
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• 1989

열전달 분야 중에서도 대류열전달에 관련된 수치해석적 연구가 현재 국제적으로 많은 연구의 대상이 되고 있으므로 이번 기회에 국내에서 수치적 방법을 이용한 대류열전달 분야의 연구동 향을 간략히 기술하고자 한다. 대류열전달 분야를 소분류하는 방법에는 여러 가지가 있겠으나 이번 조사에서는 "자연대류 열전달", "강제대류 열전달" 그리고 "상변화 열전달"의 세 가지로 분 류하였으며 위의 분류에 명확히 속하지 않는 것이라고 유사성을 참고하여 분류하였다. 상기 각 분야에서의 기술 순서는 대략적으로 발표년도 순서를 따랐다. 본 연구동향의 조사에서는 국내 학술 문헌중 "대한기계학회논문집"을 중심으로 하여 이외에 관련된 학술지로서 "공기조화. 냉동 공학", "태양에너지"등에 수록된 논문을 발췌 요약하였다.uot;공기조화. 냉동 공학", "태양에너지"등에 수록된 논문을 발췌 요약하였다.된 논문을 발췌 요약하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.1021-1029
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• 1991

본 연구에서는 2차원 정사각형 밀폐공간내에서 흡수 및 방사하는 회기체에 대 한 자연대류-복사 열전달을 P-1 및 P-3 근사법을 이용하고 수치해석을 통하여 유동 및 열전달 특성을 연구하였고 Plank 수, 광학두께 및 벽방사율의 영향을 조사하였다. 또한 P-3 근사해와 비교함으로써 P-1 근사해의 적용범위를 고찰하였다.

• Solar Energy
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• v.15 no.3
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• pp.39-52
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• 1995

This study is investigated numerically on the heat transfer characteristics of surface radiation-natural convection interactions in a two dimensional enclosure assumed Ondol cavity. Mean Nusselt number of the bottom surface with surface radiation is increased by increasing wall emissivity and by decreasing dimensionless thickness of adiabatic wall. and is greater than that without radiation. Mean Nusselt number of the bottom surface for convection only with surface radiation is slightly smaller than that without surface radiation with decrease dimensionless thickness of adiabatic wall.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.945-952
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• 1990

본 연구에서는 수치해석을 위한 2차원 형상을 선정하여 휜의 길이와 간격을 변수로 수직평판휜이 상향 또는 하향으로 부착된 수평평판에서의 자연대류 열전달특성 을 고찰하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.701-708
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• 2011

Natural convection heat transfers on inclined flat plates were measured for Grashof numbers of $8.06{\times}10^7$ and $3.45{\times}10^9$ by using a copper sulfate electroplating system. The inclinations of the plates were varied from upward-facing horizontal to downward-facing horizontal. Test results for the downward-facing plate agree well with the existing theory that the Nusselt number can be calculated by replacing gravitational acceleration, g with g $cos{\theta}$ in the heat transfer correlation for the vertical plate. The natural convection flows for the upward-facing plate follow two distinct flow regimes: boundary layer regime and flow separation regime. The copper plating pattern for the upward-facing plates clearly reveals the flow separation points.