• 에너지공학
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• 제22권1호
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• pp.8-16
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• 2013

A core catcher is considered as a promising engineered system to stabilize the molten corium in the containment during a postulated severe accident in a nuclear power plant. Conceptually, the core catcher consists of a carbon steel body, sacrificial material, protection material, and engineered cooling channel. The cooling capacity of the engineered cooling channel should be guaranteed to remove the decay heat of the molten corium. The flow in ex-vessel core catcher is a combined problem of a two-phase flow in the engineered cooling channel and a single-phase natural circulation in the whole core catcher system. In this study, the analysis of the test facility for the core catcher using the CUPID code, which is a three-dimensional thermal-hydraulic code for the simulation of two-phase flows, was carried out to evaluate its cooling capacity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.607-612
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• 2001

Based on the flow characteristics around a piercing cylinder, a free surface-flow velocitmetry which can be used in extremely harsh environment such as molten steel flow was developed. The velocimetry is consisted of finite length cylinder, load detecting elastic plate, electric signal transducer and data acquisition H/W and S/W. Using such a velocimetry, two velocity measurement schemes were established which one is flow resistance detecting scheme and the other is Karman Vortex frequency detecting scheme. For calibration of each scheme, realistic flow water model was used and in followings, detailed calibration processes were explained.

• Tribology and Lubricants
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• 제33권6호
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• pp.256-262
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• 2017

Molten zinc plating is a process in which zinc is thinly coated over a metallic or non-metallic surface. It is used in various industrial fields for corrosion resistance and decoration. During the process, a steel sheet is passed through a roll that rotates inside the molten zinc liquid in the temperature range of $460^{\circ}C$ to $680^{\circ}C$, and the plating liquid flows into the roll causing abrasion and erosion of the roll surface. This problem is known to accelerate the replacement cycle of the roll and cause considerable economic loss owing to production line stoppage. Here, we propose a mechanism that operates at high temperature and pressure with a labyrinth type seal design to resolve this problem. We theoretically investigate the flow of the plating solution inside the seal and compute the minimum rotation speed required to prevent the plating solution from entering the seal chamber. In addition, we calculate the thermal deformation of the seal during operation and display thermally deformed dimensions at high temperatures. To verify the theoretical results, we perform experiments using pilot test equipment working in the actual plating environment. The experimental results are in good agreement with theoretical results. We expect our results to contribute towards the extension of the roll's life span and thereby reduce the economic losses.

• 설비공학논문집
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• 제11권6호
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• pp.766-773
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• 1999

A numerical analysis has been performed solidification problem using the fixed grid-enthalpy method with enthalpy-porosity relation. A modified standard $k-\varepsilon$ model was applied to describe the influence of turbulent flow. Computational procedures are based on the finite volume method and the non-staggered grid system. Comparisons with the different three experimental results show that applying a modified standard $k-\varepsilon$model in mushyzone is better than the previous computation results. This paper includes another EMBR's influences such as change of velocity field, Increasement of temperature and dispersion of flow out of nozzle into the flow field. These EMBR's influences are compared to case without EMBR.

• 대한금속재료학회지
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• 제50권2호
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• pp.129-135
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• 2012

High speed casting technology is an attractive method to increase the productivity of continuous casting. However, high speed casting causes flow instability of molten steel in a mold. In this study, Large Eddy Simulation (LES) has been performed to identify the characteristics of mold flow for various shapes of submerged entry nozzles. The LES code has been newly developed to efficiently compute the two-phase flow by using the Fractional Step Method (FSM) combined with the Volume of Fluid (VOF) method. The Immersed Boundary Method was used to implement the shape of the submerged entry nozzle. Three cases of discharge angle of the submerged entry nozzle were computed and compared. The current results shed light on improving shape design of a submerged entry nozzle.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.922-934
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• 2014

In casting steels for offshore construction, manufacturing integral casted structures to prevent fatigue cracks in the stress raisers is superior to using welded structures. Here, mold design and casting analysis were conducted for integral casting steel. The laminar flow of molten metal was analyzed and distributions of hot spots and porosities were studied. A prototype was subsequently produced, and air vents were designed to improve the surface defects caused by the release of gas. A radiographic test revealed no internal defects inside the casted steel. Evaluating the chemical and mechanical properties of specimens sampled from the product revealed that target values were quantitatively satisfied. To assess weldability in consideration of repair welding, the product was machined with grooves and welded, after which the mechanical properties of hardness as well as tensile, impact, and bending strengths were evaluated. No substantive differences were found in the mechanical properties before and after welding.

• 자원리싸이클링
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• 제1권1호
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• pp.37-43
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• 1992

The submerged injection smelting process was performed to recover Zn and Pb from steel dust throuth vaporization and to investigate the effect of temperature, slag composition, injection time, gas flow rate, etc. on the recoveries of valuable metals. The results show that vaporation rates of zinc and lead increased at higher temperture and higher moral ratio of ferrous to ferric oxides. In the initial stage of submerged injection of nitrogen gas, the molten slags of the dust have high value of molar ratio of $Fe^{2+}$/$Fe^{3+}$ and hence zinc and lead can be effectively recovered.

• 한국전산유체공학회지
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• 제10권1호
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• pp.56-62
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• 2005

Large eddy simulation of vortexing flow of molten steel in the continuous casting mold with and without DC magnetic field was conducted. The influence of the position of magnetic field to the residence time and depth of the vortex was analyzed. The mechanism of the influence of magnetic field to the vortexing flow was found. The computational results show that the vortexing flow is the result of shearing of the two un-symmetric surface flows from the mold narrow faces when they meet adjacent to the SEN; the un-symmetric flow for turbulent vortex is caused by turbulent energy of the fluid and that for biased vortex is caused by biased flow and the turbulent energy of fluid; with the moving of the magnetic field from the centerline of the outlet of the SEN to the free surface, the surface velocity is decreased gradually and the depth of the turbulent vortex and the biased vortex is decreased, the residence time is increased with the magnetic field moves from DL=120mm to DL=60mm and then decreased; the turbulent vortex and the biased vortex can be eliminated when the magnetic field is located at the free surface.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1265-1273
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• 1999

PIV(Particle Image Velocimetry) velocity field measurements inside the snout of a1/10 scale model of the Zn plating process were carried out at the strip speed $V_s=1.5m/s$. Aluminum powder particles ($1{\mu}m$) and atomized olive oil ($3{\mu}m$) were used as seeding particles to simulate the molten Zinc flow and deoxidization gas flow, respectively. A pulsed Nd:Yag laser and a $2K{\times}2K$ high-resolution CCD camera were synchronized for the PIV velocity field measurement. From flow visualization study, it is found that the liquid flow in the Zn pot is dominantly governed by the uprising flow caused by the rotating sink roll, with its effect on the steel strip inside the snout largely diminished by installing of the snout. The deoxidization gas flow in front of the strip inside the snout can be characterized by a large-scale vortex rotating clockwise direction formed by the moving strip. In the rear side of the strip, a counter-clockwise vortex is formed and some of the flow entrained by the moving strip impinges on the free surface of molten zinc. The liquid flow in front of the strip is governed by the flow entering the snout, caused by the spinning sink roll. Just below the free surface a counter-clockwise vortex is formed near the snout wall. The moving strip affects dominantly the flow behind the strip inside the snout, and large amount of the liquid flow follows the moving strip toward the sink roll. The thickness of the flow following the strip is very thin in the front side due to the uprising flow, however thick boundary layer is formed in the rear side of the strip. Its thickness is increased as moving downstream toward the sink roll. Inside the snout, the deoxidization gas flow above the free surface is much faster than the liquid flow in the zinc pot. Due to the larger influx of the flow following the moving strip in the rear side of the strip, higher percentage of imperfection can be anticipated on the rear surface of the strip.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.639-643
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• 2002

The main purpose of this study was to investigate the formation mechanisms of imperfections such as irregular humps, outer cavity and inner cavity in the laser fusion zone of diamond saw blade. Laser beam welding was conducted to join two parts of blade; mild steel shank and Fe-Co-Ni sintered tip. The variables were beam power and travel speed. The microstructure and elements distributions of specimens were analyzed with SEM, AES, EPMA and so on. It was found that these imperfections were responded to heat input. Irregular humps were reduced in 10.4∼17.6kJ/m heat input range. However there were no clear evidences, which could explain the relations between humps formation and heat input. The number of outer cavity and inner cavity decreased as heat input was increased. Considering both possible defects formations mechanisms, it could be thought that outer cavity was caused by insufficient refill of keyhole, which was from rapid solidification of molten metal and fast molten metal flow to the rear keyhole wall at low heat input. More inner cavities were found near the interface of the fusion zone and sintered segment and in the bottom of the fusion zone. Inner cavity was mainly formed in the upper fusion zone at high heat input whereas was in the bottom at low heat input. Inner cavity was from trapping of coarsened preexist pores in the sintered tip and metal vapor due to rapid solidification of molten metal before the bubbles escaped.