• 대한기계학회논문집B
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• 제41권1호
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• pp.1-8
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• 2017

대기압 하에서 포화 상태를 유지하는 물의 내부에 잠긴 탠덤 튜브에 적용하기 위한 실험적 상관식을 새롭게 개발하였다. 상관식은 다발효과를 계산하기 위한 것으로 실험에서 측정한 값과 최소자승법을 사용하여 결정하였다. 상관식의 적절함을 평가하기 위해 통계분석을 수행하였다. 상관식은 실험값을 ${\pm}8%$ 범위 내에서 잘 예측함을 확인하였다. 상관식의 적용 범위는 피치=28.5~114mm, 방위각=$0^{\circ}{\sim}90^{\circ}$, 경사각=$0^{\circ}{\sim}90^{\circ}$, 상부 및 하부 튜브 열유속=$0{\sim}120kW/m^2$이다.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.751-757
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• 2016

The present work discusses two different models of boiling water reactor (BWR) bundle to compare the neutronic characteristics of uranium dioxide ($UO_2$) and uranium zirconium hydride ($UZrH_{1.6}$) fuel. Each bundle consists of four assemblies. The BWR assembly fueled with $UO_2$ contains $8{\times}8$ fuel rods while that fueled with $UZrH_{1.6}$ contains $9{\times}9$ fuel rods. The Monte Carlo N-Particle Transport code, based on the Mont Carlo method, is used to design three dimensional models for BWR fuel bundles at typical operating temperatures and pressure conditions. These models are used to determine the multiplication factor, pin-by-pin power distribution, axial power distribution, thermal neutron flux distribution, and axial thermal neutron flux. The moderator and coolant (water) are permitted to boil within the BWR core forming steam bubbles, so it is important to calculate the reactivity effect of voiding at different values. It is found that the hydride fuel bundle design can be simplified by eliminating water rods and replacing the control blade with control rods. $UZrH_{1.6}$ fuel improves the performance of the BWR in different ways such as increasing the energy extracted per fuel assembly, reducing the uranium ore, and reducing the plutonium accumulated in the BWR through burnup.

• 한국안전학회지
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• 제32권2호
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• pp.147-152
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• 2017

The external reactor vessel cooling (ERVC) is well known strategy to mitigate a severe accident at which nuclear fuel inside the reactor vessel is molten. In order to compare the heat removal capacity of ERVC between the nuclear reactor designs quantitatively, numerical method is often used. However, the study for ERVC using computational fluid dynamics (CFD) is still quite scarce. As a validation study on the numerical prediction for ERVC using CFD, the subcooled boiling flow and natural circulation of coolant at the ULPU-V experiment was simulated. The commercially available CFD software ANSYS-CFX was used. Shear stress transport (SST) model and RPI model were used for turbulence closure and wall-boiling, respectively. The averaged flow velocities in the downcomer and the baffle entry under the reactor vessel lower plenum are in good agreement with the available experimental data and recent computational results. Steam generated from the heated wall condenses rapidly and coolant flows maintains single-phase flow until coolant boils again by flashing process due to the decrease of saturation temperature induced by higher elevation. Hence, the flow rate of coolant natural circulation does not vary significantly with the change of heat flux applied at the reactor vessel, which is also consistent with the previous literatures.

• 동아시아식생활학회지
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• 제19권3호
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• pp.375-383
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• 2009

This study was conducted to measure the total polyphenol contents and DPPH radical scavenging activities of different potato plants parts, varieties, and grades, and by distribution and different cooking conditions. The results were as follows. For the plant parts, total phenolic content and DPPH radical scavenging activity were highest in the flowers followed by leaves and stems, respectively. Among 5 potato varieties, 'Jasim' had the highest DPPH radical scavenging activity and the activity of its pulp was lower than that of its cortex(peel). Regardless of potato grade, the cortexes(peel) of samples had two-fold higher DPPH radical scavenging activity than pulp, and the Grade SS potato had the highest phenolic content. It was also found that the bud ends and stem ends had comparably larger amounts of phenolic compounds in horizontally cut potatoes. Finally, the descending order for DPPH radical scavenging activity, according to different cooking conditions, was as follows: gas oven range-baking, frying, microwave-heating, sauteing, boiling in 1% saline solution, steaming, and boiling in 3% saline solution.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.262-268
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• 2008

The present paper dealt with flow heat transfer characteristics of R-410A vaporization in horizontal smooth microchannel. The test sections were made of stainless steel tube with inner diameters of 300 mm and length of 300 mm. The refrigerant was supplied with mass flux range of 260-600 kg/$m^2s$ and applied under operating heat flux range of 5-20 kW/$m^2$ using a direct electric current heating method. The in let saturation temperature was set at $10^{\circ}C$ and vapor quality up to 1.0. The influences of mass flux, heat flux and inner tube diameter on local heat transfer coefficients were presented. Comparison with existing heat transfer coefficient correlations was performed. An improved heat transfer coefficient correlation for refrigerant vaporization in microchannel based on superposition model was developed with a mean deviation of 14.01%.

• 대한기계학회논문집
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• 제13권3호
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• pp.411-418
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• 1989

본 연구에서는 물 및 물을 주성분으로 하는 NaCl, $Na_{2}$CO$_{3}$, NaOH 등의 비휘발성 수용액을 담금제로 하고 KS M 2172의 열처리유 냉각성능 실험 방법에서 채택하고 있는 은시편(순도 99.9%)을 이용한 표준냉각곡선으로부터 냉각 속도 열전달계수 및 담금강열도 등 담금제의 냉각성능 파라미터를 구하였으며, 각종 담금제의 온도 및 수용액의 농도 변화에 따른 냉각성능을 평가하였다. 그리고 실험에서 채택한 시편 및 담금제를 모델로 하여 축대칭 비정상 열전도방정식을 유한 요소법에 의하여 해석하고 냉각시간에 따른 시편의 온도분포를 계산하여 실험결과와 비교하였다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1241-1250
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• 2019

This study mainly focused on the neutronics modeling of bubbles in bubbly flow in boiling water reactors. The bubble, ring and homogenous models were used for radial void fraction distribution. Effect of the bubble and ring models on the infinite multiplication factor and two-group flux distribution was investigated by comparing with the homogenous model. Square pitch unit cell geometry was used in the calculations. In the bubble model, spherical and non-spherical bubbles at random positions, sizes and shapes were produced by Monte Carlo method. The results show that there are significant differences among the proposed models from the viewpoint of physical interaction mechanism. For the fully-developed bubbly flow, $k_{inf}$ is overestimated in the ring model by about $720{\pm}6pcm$ with respect to homogeneous model whereas underestimated in the bubble model by about $-65{\pm}9pcm$ with a standard deviation of 15 pcm. In addition, the ring model shows that the coolant must be separated into regions to properly represent the radial void distribution. Deviations in flux distributions principally occur in certain regions, such as corners. As a result, the bubble model in modeling the void fraction can be used in nuclear engineering calculations.

• 한국표면공학회지
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• 제57권3호
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• pp.201-207
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• 2024

This study compared the chemical resistance properties according to various sealing treatment methods for the anode film formed during the anodization process of Al6061 alloy. Al6061 aluminum was used in four different sealing treatment methods: boiling water sealing, lithium sealing, nickel sealing, and pressurized sealing, and each sample was evaluated for corrosion resistance through a 5% HCl bubble test and the microstructure was observed through a scanning electron microscope(SEM). According to the results, corrosion resistance increased as time and temperature increased in all sealing treatment methods. Relatively, corrosion resistance was high in the order of boiling water sealing, lithium sealing, nickel sealing, and pressure sealing, and the best corrosion resistance was found in pressure sealing. These research results can be helpful in selecting a process necessary to improve the efficiency and performance of anodizing process in the industrial field using aluminum alloys.

• Nuclear Engineering and Technology
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• 제16권2호
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• pp.47-57
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• 1984

2상유동을 해석하기 위한 3차원 코드인 THERMIT-6S의 미분 방정식을 세우기 위해, 수학적으로 정확하게 유도된 시간과 공간에 대해 평균한 보존 방정식을 단순화했다. 미분 방정식을 불연속화(discretization)하여 THERMIT-6S의 차분방정식을 얻는다. First-order spatial scheme, donor cell method, 그리고, staggered mesh layout을 써서 공간에 대한 불연속화를 한다. 그리고 시간에 대한 불연속화는 first-order semi-implicit scheme으로써, sonic terms와 국부적인 전달 현상에 관계되는 항들은 implicit하게 그리고 대류 전달 항들은 explicit하게 취급한다. 이렇게 얻어진 방정식들은Newton-Raphson 방법으로 선형화된다. 축소된 압력 방정식을 만들기 위해 모든 변수들이 mesh cells사이에서 단지 압력 변수를 통해서만 결부되도록, 선형화된 방정식들을 처리한다. OPERA-15 실험을 수치해석적으로 모의실험하여 본 결과, THERMIT-6S가 flow coastdown, 역류, 유체진동(flow oscillation) 등을 포함하고, sodium boiling 후의 원자로내의 변화를 예측하는데 매우 유효하다는 것이 밝혀졌다.

• 한국응용과학기술학회지
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• 제21권3호
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• pp.214-224
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• 2004

Although the structure of carbon nanotubes is important factor characterizing its properties, it is very difficult to control the structure of carbon nanotubes (MWNTs) and to predict the range of their diameter, which is the primary factor of MWNTs' physical properties. We tried to control the diameter of MWNTsby governing the feed injection temperature of floating catalyst method. The structure of MWNTs was influenced by the phase change of ferrocene fed as the catalyst,. The carbon nanotubes were very narrow at injection temperatures close to the sublimation pt. of ferrocene, in which most MWNTs had diameters in the range of 20$^{\sim}$30 nm. At injection temperatures between the boiling pt. and melting pt. of ferrocene, the diameters became larger and had broad distribution. However, at injection temperatures higher than the boiling pt., the diameters became narrow again and had very uniform distribution.