• Nuclear Engineering and Technology
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• v.46 no.3
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• pp.395-406
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• 2014

This study provides a fundamental understanding of a cold finger melt crystallization technique by exploring the heat and mass transfer processes of cold finger separation. A series of experiments were performed using a simplified LiCl-CsCl system by varying initial CsCl concentrations (1, 3, 5, and 7.5 wt%), cold finger cooling rates (7.4, 9.8, 12.3, and 14.9 L/min), and separation times (5, 10, 15, and 30 min). Results showed a potential recycling rate of 0.36 g/min with a purity of 0.33 wt% CsCl in LiCl. A CsCl concentrated drip formation was found to decrease crystal purity especially for smaller crystal formations. Dimensionless heat and mass transfer correlations showed that separation production is primarily influenced by convective transfer controlled by cooling gas flow rate, where correlations are more accurate for slower cooling gas flow rates.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.289-297
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• 2009

We numerically analyzed flow characteristics of the polymer melt in the screw equipment using a proper modeling and investigated design parameters which have influence on the mixing performance as the capability of the screw equipment. We considered the non-Newtonian and non-isothermal flow in a single rotor equipment to investigate the mixing performance with respect to screw dimensions as shape parameter of the single rotor equipment and screw speed as process parameter. We used Bird-Carreau-Yasuda model as a viscous model of the polymer melt and the particle tracking method to investigate the mixing performance in the screw equipment and considered four mixing performance indexes: residence time distribution, deformation rate, total strain and particle standard deviation as a new mixing performance index. We compared these indexes to determine design parameters and object function. On basis of the analysis results, we carried out the optimal design by using the response surface method and design of experiments. In conclusion, the differences of results between the optimal value and numerical analysis are about 5.0%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1308-1318
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• 1995

The influence of varying rotation speed of both crystal and crucible was numerically investigated for the Czochralski silicon-crystal growth. Based on a simplified model assuming flatness of free surfrae, the Navier-Stokes Boussinesq equations were employed to identify the flow pattern, temperature distribution as well as the shape of the melt/crystal interface. The present results showed that the interface shape was relatively convex with respect to the melt at lower pulling rate and tended to be concave as the pulling rate increased. In particular, the experimentally observed gull-winged shape of the interface was qualitatively in agreement with the predicted shape. The rotation of crystal alone little affected the growth system. When the rotation speed of the crucible was increased, there occurred inversion of the interface shape from convex to concave pattern. At rapid rotation of the crucible, an interesting channel formation was predictied primarily due to the assumption of laminar flow.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.73-81
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• 1997

This study was to find the best adhesive condition comparing mechanical property in case of hot-melt adhesion using glue-gun, ultrasonic welding with adhesion and only ultrasonic welding in order to adhere thermoplastic resin of polyethylene (PE) in which reliable adhesion was resulted in case of ultrasonic welding with same materials of PE. The best welding condition were acquired at welding time 1 second, welding pressure 250kPa for PE-PE where welding time and welding pressure were increased in accordance with the increase of material strength. At the best ultrasonic welding conditions, bonding strength of PE-PE welding was about 21MPa of which material have tensile strength of 24MPa. Through the analysis of microscophic test for ultrasonic welding structure, it was distinguished between well welded structure with higher intermolecule flow and bad welded structure with lower flow, of which result is mostly correspond with the result of tensile strength test.

• Journal of Korea Foundry Society
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• v.13 no.5
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• pp.424-431
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• 1993

A Numerical technique has been developed for the coupled heat transfer and fluid flow calculation during the casting process. In this method the SMAC technique was coupled with the concept of Volume of Fluid(VOF) to calculate melt free surface and velocity profiles within the melt, and the Energy Marker method coupled with the finite difference method was proposed for the convective and conductive heat transfer analysis in the casting. When comparing numerical calculations with experimental observations, a close correlation was evident. It has been shown that this technique is useful for proper gating and casting design, especially for thin-walled castings.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.267-273
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• 2011

Erosion and thermal shock resistance of several refractory materials have been investigated, which are expected to be used as nozzles in a planar flow casting equipment for amorphous alloys. The test was conducted on five materials; graphite, boron nitride, fused silica, alumina and zirconia. Test specimens were preheated and dipped into the melt of carbon steel and amorphous alloys. Some test specimens were rotated to develop high erosion and to shorten the test periods. Fused silica and boron nitride specimens showed the excellent erosion and thermal shock resistance irrespective of the kind of melt and melting atmosphere.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.5
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• pp.945-952
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• 2023

In this study, the sand casting process was applied to design the gating system and perform casting simulation in order to domestically produce the submarine mast cover. Based on simulation results, casting experiments were conducted to produce a soundness prototype. The design concept of the mast cover's gating system was based on the design of bell casting. By arranging eight tower-type gates in a circle at 45° intervals, the flow of melt flowing into each gate was uniform and did not mix with each other, and the velocity of melt was also uniform. The mast cover made of Ni-Al-Bronze alloy has no unfilled parts. However, small porosities and flow marks occurred on the surface in several places. Yield strength and ultimate tensile strength are 279.3 MPa and 675.7 MPa, respectively, and elongation is 21.2%.

• Design & Manufacturing
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• v.17 no.4
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• pp.57-62
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• 2023

As a representative method for mass production, a multi-cavity type mold capable of simultaneously molding products of the same shape can be applied. It has the advantage of improving the productivity from several times to several tens of times, but it may cause disadvantages which is the quality deviation with each cavity. This study, therefore, has tried to increase the cavity filling balance by using a melt flipper and a flow distance control part in the runner part of the mold. Along with this, the design and manufacturing of air vents during injection molding have been verified through experimental methods to achieve a higher level of multi-cavity filling balance and dimensional accuracy.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.27-40
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• 1997

The heat in Czochralski method is transfered by all transport mechanisms such as convection, conduction and radiation and convection is caused by the temperature difference in the molden pool, the rotations of crystal or crucible and the difference of surface tension. This study delvelops the simulation model of Czochralski growth by using the finite difference method with fixed grids combined with new latent heat treatment model. The radiative heat transfer occured in the surfce of the system is treated by calculating the view factors among surface elements. The model shows that the flow is turbulent, therefore, turbulent modeling must be used to simulate the transport phenomena in the real system applied to 8" Si single crystal growth process. The effects of a cusp magnetic field imposed on the Czochralski silicon melt are studied by numerical analysis. The cusp magnetic field reduces the natural and forced convection due to the rotation of crystal and crucible very effectively. It is shown that the oxygen concentration distribution on the melt/crystal interface is sensitively controlled by the change of the magnetic field intensity. This provides an interesting way to tune the desired O concentration in the crystal during the crystal growing.

• Carbon letters
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• v.2 no.3_4
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• pp.170-175
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• 2001

A petroleum-based isotropic pitch fiber spun by melt-blown method was oxidized in air flow at various conditions. The oxidized pitch fiber obtained was tested for its infusibility and its elemental composition during the process of stabilization. The structural changes were traced by using solvent solubility, FT-IR spectroscopy, and elemental analysis. The samples showed a gradual increase in weight with increasing the oxidization temperature. The weight gain of sample oxidized at $320^{\circ}C$ for 10 min was about 4.5%. The concentration of the pyridine and toluene soluble fraction decreased with an increase in stabilization temperatures. The oxygen uptaken in the stabilization process converted aliphatic side chains into the carbonyl groups. As stabilization proceeded, the more ether and carboxylic acid groups were formed through the oxidations of aldehyde and primary alcohol, and then the carboxylic acid was dehydrated to be aromatic anhydride.