• 대한기계학회논문집
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• 제11권1호
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• pp.105-109
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• 1987

본 연구는 열교환기의 설치 및 사용목적에 따라 전열관내유동이 경사류가 될 때 특히 자연순환(2*$10^{6}$＜Gr＜15*$10^{6}$)의 경우와 강제순환(3,000＜Re＜ 40,000)의 경우에 대해서 열전달특성과 유동마찰에 의한 손질을 규명하는데 있다. 사용되는 관은 평골관과 ribbed관이며 관경사각을 수평면에 대하여 0˚,22.5˚,45˚, 90˚로 변화시켰다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권7호
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• pp.702-708
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• 2015

본 연구에서는 FC-72를 작동 유체로 사용하여 이상 유동 비등에 관한 실험을 수행하였다. 마이크로 채널은 깊이 0.2mm, 폭 0.45mm, 길이 60mm 그리고 채널의 개수는 15개로 구성되었다. 실험은 질량유속과 열유속 각각 $200-400kg/m^2s$, $5.6-49.0kW/m^2$ 범위와 증기 건도 0.02-0.93 범위에서 수행되었다. 실험 결과에 따르면 낮은 건도(x<0.2)영역에서는 핵비등에 의한 열전달이 지배적으로 작용하며, 그 이상의 증기 건도 영역에서는 핵비등과 강제 대류 비등의 영향이 복합적으로 작용하는 것으로 나타났다. 핵비등과 강제 대류 비등은 각각 비등수와 대류수에 관한 함수로 표현할 수 있으며, 실험에서 얻어진 열전달 계수는 기존의 상관식에 의한 열전달 계수와 비교하였다.

• 한국추진공학회지
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• 제13권1호
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• pp.51-57
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• 2009

이 연구 논문에서는 위상최적화 방법을 사용하여 강제대류를 이용한 열소산하는 구조물을 설계하는 방법을 개발한다. 전기 부품이나 기계구조물에서 발생하는 열을 낮추기 위해서 자연 대류와 강제 대류가 넓게 사용되고 있다. 또한 현재에는 화학전지(Fuel cell)나 로켓의 추진기관 등에서 발생한 열을 낮추기 위해서 강제 대류를 사용하고 있다. 현재에 이런 시스템을 효과적으로 열을 소산시키기 위해서 유동의 채널을 설계하는 것이 아주 중요한 이슈로 다루어지고 있다. 따라서 이 논문에서는 위상최적화 기법을 사용하여 최적의 채널을 설계하는 연구를 수행한다. 대류 현상을 고려하기 위해서 비압축성 N-S 방정식의 해석을 수행하였다. 이 논문에서는 열과 유체가 연계되어 있는 시스템을 수치적으로 연구하고 강제대류를 고려하는 최적의 채널 설계 결과를 제시한다.

• 한국정밀공학회지
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• 제19권11호
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• pp.146-159
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• 2002

An efficient method to predict the convection heat transfer coefficients on the top surface of the engine piston is proposed. The method is based on the inverse method of the thermal conduction problem and uses a numerical optimization technique. In the method, the heat transfer coefficients are numerically obtained so that the difference between analyzed temperatures from the finite element method and measured temperatures is minimized. The method can be effectively used to analyze the temperature distribution of engine pistons in case when application of prescribed-temperature boundary condition is not reasonable because of insufficient number of measured temperatures. A hollow sphere problem with an analytic solution is taken as a simple example and accuracy and efficiency is demonstrated. The method is applied to a practical large liquid petroleum gas(LPG) engine piston and the heat transfer coefficients on the top surface of the piston is successfully calculated. Resulting analyzed temperature favorably coincides with measured temperature.

• 설비공학논문집
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• 제14권11호
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• pp.923-930
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• 2002

Cooling characteristics of a parallel channel with protruding heat sources using convection and conduction heat transfer are studied numerically. A two-dimensional model has been developed for numerical prediction of transient, compressible, viscous, laminar flow, and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve the problem. The assembly consists of two channels formed by two covers and one printed circuit board which has three uniform heat source blocks. Six different cooling methods are considered to find out the most efficient cooling method in a given geometry and heat sources. The velocity and temperature fields of cooling medium, the temperature distribution along the block surface, and the maximum temperature in each block are obtained. The results are compared to examine the cooling characteristics of the different cooling methods.

• 대한기계학회논문집B
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• 제21권2호
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• pp.235-251
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• 1997

A numerical simulation on the combined natural convection and radiation is carried out in a partially open rectangular enclosure with a heater by using the finite volume and the S-8 discrete ordinate methods. The fluid inside the enclosure is considered as an absorbing, emitting and anisotropic scattering media. The heater causes a natural circulation of the fluid (10$^{5}$ $^{9}$ ) which results in significant in-flow of the ambient cold fluid through the partially open wall. Comparing the results of pure convection with those of the combined convection- radiation, the combined heat transfer results with small Planck numbers (P$_{l}$ <1.0) show much stronger circulation than those of the pure convection, and the fluid circulation is more evident for larger Rayleigh numbers. When one of three radiative properties - the medium absorption coefficient, the wall reflectivity, and the scattering albedo - increases, the fluid circulation and the heat transfer in the enclosure are reduced. The location of the heater and the open ratio of the right wall are also shown to affect the fluid circulation and heat transfer significantly. However, the anisotropy of the scattering phase function is shown to be unimportant for the fluid circulation and heat transfer within the enclosure considered in this study.

• 대한기계학회논문집B
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• 제35권1호
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• pp.43-51
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• 2011

수평관 외부에서 발생하는 자연대류 열전달 현상을 실험적으로 연구하였다. 연구의 목적은 구리 도금계를 채택한 유사성실험방법론이 적용가능한지 확인하는 것과 수평관의 지름과 각도에 따라 달라지는 국부열전달을 시각화하는 것이었다. 구리의 전기도금계를 사용하면 양극에서 생성된 구리이온은 대류와 확산을 통하여 음극으로 이동되어 환원되는데 이는 열전달을 모사하게 된다. 구리와 색깔이 다른 알루미늄을 음극으로 채택함으로써 각도에 따라 환원되어 석출된 구리의 양을 시각화 할 수 있었다. 수평관의 직경은 0.01m에서 0.15m이었고 이는 $Ra_D\;=\;1.73{\times}10^7\;{\sim}\;5.69{\times}10^{11}$에 해당한다. 실험결과는 기존에 알려진 열전달 상관식과 일치하였다. 알루미늄 음극에 도금된 구리의 패턴은 Kitamura에 의해 액체결정온도측정법으로 시각화한 결과와 매우 잘 일치 하였다.

• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2997-3009
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• 2023

The Passive containment Air-cooling System (PAS) can effectively remove the decay heat of the modular small nuclear reactor after an accident. The details of natural convection around the dome, which is a key part of PAS, were investigated numerically in the present study. The thermal dynamics around the dome were studied through the temperature, pressure and velocity contours and the streamlines. Additionally, the formation of the buoyant plume at the top of the dome was investigated. The results show that with the increase of Ra, the lift-off point moves toward the bottom of the dome, and the eddy under the buoyant plume grows larger gradually, which enhances the heat transfer. And the heat transfer along the dome surface with different truncation angles was investigated. As the angle increases, the heat transfer coefficient becomes stronger as well. Consequently, a newly developed heat transfer correlation considering the influence of truncation angle for the dome is proposed based on the simulated results. This study could provide a better understanding of natural convection around the dome of PAS and the proposed correlation could also offer more predictive value in the improvement of nuclear safety.

• 한국분무공학회지
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• 제13권3호
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• pp.143-148
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• 2008

In the present study, the correlation between the Nusselt number and Reynolds number was developed for forced convection and nucleate boiling region in spray cooling. Also the effect of droplet subcooling on spray cooling heat transfer was investigated. Full cone spray nozzles were employed for spray cooling experiment, and water and FC-77 were used for developing the correlation. From the experimental results, the correlation between the Nusselt number and Reynolds number based on droplet-flow-rate was developed. The correlation shows good predictions with ${\pm}30%$ error for water and FC-77.

• 설비공학논문집
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• 제3권5호
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• pp.365-375
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• 1991

Confined natural convection due to lateral temperature difference in rectangular enclosures was studied numerically and experimentally for the insulated and the constant temperature enclosures. In the case of insulated enclosure, the flow pattern and heat transfer modes are rather simple depending mainly upon Rayleigh number. In the case of isothermal enclosure, however, the phenomena of flow and heat transfer are somewhat complex and interesting due to the stable thermal gradients and various circumstances resulted from four wall temperature conditions. As a dimensionless variable, to describe properly the flow and heat transfer phenomena in the isothermal enclosure, temperature difference ratio ${\Delta}T_v/{\Delta}T_H$ is newly introduced and this parameter seems to be appropriate in the analysis of results on the effect of stabilizing thermal gradient.