• Korean Journal of Metals and Materials
• /
• v.47 no.11
• /
• pp.734-739
• /
• 2009

It is well known that the temperature and the flow pattern of the crystal-melt interface affect the qualities of the single crystal in the Czochralski process. Thus the temperature profile in the growth system is very important information. This work focuses on controlling the temperature of the silicon melt with a thermal gradient of the crucible. Therefore, the side heater is divided into three parts and an extra heater is added at the bottom for thermal gradient. The temperature of the silicon melt can be strongly influenced and controlled by the electric power of each heater.

• Nuclear Engineering and Technology
• /
• v.38 no.1
• /
• pp.1-10
• /
• 2006

The interaction and mixing of high-temperature melt and water is the important technical issue in the safety assessment of water-cooled reactors to achieve ultimate core coolability. For specific advanced light water reactor (ALWR) designs, deliberate mixing of the core-melt and water is being considered as a mitigative measure, to assure ex-vessel core coolability. The paper provides the background of past experiments as well as key fundamentals that are needed for melt-water interfacial transport phenomena, thus enabling the development of innovative safety technologies for advanced LWRs that will assure ex-vessel core coolability.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.3
• /
• pp.177-184
• /
• 2000

The effect of the buyancy and thermocapillarity for differnent aspect ratio of flow field on melt motion and mass transfer has been numerically investigated in magnetic Czochralski crystal growth of silicon. During the process of crystal growth, the melt depth of crucible reduces so the aspect ratio of flow field also reduces. Therefore the shape of magnetic field of the flow field changes and the flow pattern also changes significantly. Together with the melt flow which forms the Marangoni convection (or thermocapillary flow) that comes from the inside the flow field, a flow circulation is observed near the corner close both to the crucible wall and the free surface. Due to this circulation, buoyancy effect has been turned out to be local rather than global. As the aspect ratio decreases, the radial component of the magnetic field prevails compared with the axial component in the flow field. Under the influence of this magnetic field, the melt flow and the temperature distribution in a meridional plane tend to depend on the radial position. As the aspect ratio decreases, the temperature gradient near the edge of the crystal decreases yielding smaller thermocapillarity, and the oxygen concentration near the crystal and the oxygen incorporation rate also decrease.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.7
• /
• pp.719-725
• /
• 2014

In the present study, a numerical analysis of an injection molding process was conducted for predicting the mold deformation considering non-Newtonian flow, heat transfer, and structural behavior. The accurate prediction of mold deformation during the filling stage is important to successfully design and manufacture a precision injection mold. While the local mold deformation can be caused by various factors, a pressure induced by the polymer melt is considered to be one of the most significant ones. In this regard, the numerical simulation considering both the melt filling and the mold deformation was carried out. A mold core for a 2D axisymmetric center-gated disk was used for the demonstration of the present study. The flow behavior inside the mold cavity and temperature distribution were analyzed along with the core displacement. Also, a Taguchi method was employed to investigate the influence of the relevant parameters including flow velocity, mold core temperature, and melt temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.2
• /
• pp.149-156
• /
• 1999

An experimental simulation on the flow in Czochralski melt using a cold model was carried out to obtain the velocities of fluid flow which affects the oxygen concentration of Czochralski crystal growing system. Low melting point Woods metal with similar Pr number to the silicon melt was adopted as a working fluid. Local flow velocities at numerous positions in the melt were simulataneously measured in three dimension using incorporated magnet probe. The measured velocity field showed a non-axisymmetric pattern dominated by natural convection. The analysis on the correlation between data set of temperatures simultaneously measured at two melt positions showed that the values of correlation coefficients were smaller than those of previous study on the small size of silicon melt and these phenomena are believed to occur because turbulent behavior becomes stronger in large size of the melt.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.86.4-86
• /
• 2001

This paper presents the results of a visualization analysis of the correlation between the fiber orientation and flow pattern in injection molding using the Gate-magnetization method developed for the precise visualization of melt flow. The results of the comparisons of the fiber orientation angles with the flow patterns by the Gate-Magnetization method for GPPS mixed with glass fibers show the strong correlation between the flow patterns and fiber orientation angles. According to forward movement of the flow, the fiber orientation patterns move toward the side walls following the flow patterns. These results elucidate that fibers are oriented in the expansion process of the melt, and ...

• Nuclear Engineering and Technology
• /
• v.54 no.1
• /
• pp.162-176
• /
• 2022

In Lead-based reactor (LBR) severe accident, the meltdown and migration inside the reactor core will lead to fuel fragment concentration, which may further cause re-criticality and even core disintegration. Accurately predicting the migration and solidification behavior of melt in LBR severe accidents is of prime importance for safety analysis of LBR. In this study, the Moving Particle Semi-implicit (MPS) method is validated and used to simulate the migration and solidification behavior. Two main surface tension models are validated and compared. Meanwhile, the MPS method is validated by the L-plate solidification test. Based on the improved MPS method, the migration and solidification behavior of melt in LBR severe accident was studied furthermore. In the Pb-Bi coolant, the melt flows upward due to density difference. The migration and solidification behavior are greatly affected by the surface tension and viscous resistance varying with enthalpy. The whole movement process can be divided into three stages depending on the change in velocity. The heat transfer of core melt is determined jointly by two heat transfer modes: flow heat transfer and solid conductivity. Generally, the research results indicate that the MPS method has unique advantage in studying the migration and solidification behavior in LBR severe accident.

• Fibers and Polymers
• /
• v.4 no.3
• /
• pp.107-113
• /
• 2003

The branched polypropylene (b-PP) was prepared by melt blending process with initiator, antioxidant, and functional monomers to improve the melt strength through the melt grafting. The melt flow index (MFI) of the b-PP was increased with increasing the initiator content. On the introduction of the alkylamine as the branching agents the MFI of the b-PP was increased, while that of the b-PP with the pentaerythritol triacrylate (PT) was decreased. It may be caused by the chain scission of the i-PP backbone due to the reduced thermal stability of the i-PP on the melt blending. The MFI of the b-PP without the antioxidant was increased due to the chain scission occurred during the melt processing, while on the introduction of the antioxidant, the MFI of the b-PP was decreased. The crystallization temperature of the b-PP was higher than that of PP, which was attributed to the branched chain structure. It was found that the PT was the most effective functional monomers for enhancing the melt properties of the b-PP.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.5 no.4
• /
• pp.306-317
• /
• 1995

Abstract Gallium arsenide crystal is usually grown from the melt by the horizontal Bridgman method. We constructed pseudo - steady - state model for crystal growth of GaAs which inclue melt, crystal and the free interface. Mathematical equations of the model were solved for flow, temperature, and concentration field in the melt and temperature field in the crystal. The location and shape of the interface were also solved simultaneously. In 2 - dimensional model, the shape of the interface is flat with adiabatic thermal boundary condition, but it becomes curved with completely conducting thermal boundary condition. In 3 - dimensional model, the interface is less curved than 2 - dimensional case and the flow intensity is similar to that of 2 - dimensional case. With the increase of flow intensity vertical segregation shows maximum value in both 2 - and 3 - D model. However, the maximum value occurs in lower flow intensity in 2 - D model because the interface is more curved for the same flow intensity.

• Korea-Australia Rheology Journal
• /
• v.20 no.2
• /
• pp.79-88
• /
• 2008

In this study, we focus on the improvement of the filling efficiency in injection molding by application of ultrasonic vibration. While studies about the filling efficiency of typical filling processes in the injection molding have been widely performed, there have been only few studies about the filling efficiency of an ultrasonic process. The effect of the ultrasonic vibration is an important process condition, which influences the flow characteristics of polymer melt. This new condition even affects well-known injection conditions such as cavity pressure, injection temperature and mold temperature. For this study, we carried out a numerical analysis by appropriate modeling and analysis of the ultrasonic process in the filling process. To verify this numerical analysis, we compared the numerical results with the experimental data. Also, we analyzed the filling process in a thin cavity using this numerical analysis. To understand the flow characteristics of polymer melt in the ultrasonic process, we substituted real and complex vibration conditions with simplified and classified conditions according to the position of vibrating cavity surfaces and the phase difference between two opposing cavity surfaces. We also introduced MFR (melt flow ratio) as a new index to estimate the filling efficiency in the ultrasonic process.