• 대한기계학회논문집B
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• 제20권7호
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• pp.2397-2408
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• 1996

A numerical study was made of the control of transient oscillatory flow modes in Czochralski convection. The reduction of temperature oscillation was achieved by changing the rotation rate of crystal rod, .OMEGA.$_{S}$=.OMEG $A_{S0}$(1+ $A_{S}$sin(2.pi. $f_{S}$/ $t_{p}$t)). The temporal behavior of oscillation flow was scrutinized over broad ranges of two parameters, i.e., the rotation amplitude( $A_{S}$.leq.0.5) and the nondimensional frequency (0.9.leq. $f_{S}$.leq.1.5). The mixed convection parameter was ranged 0.225.leq.Ra/PrR $e^{2}$.leq.0.929, which encompassed the buoyancy-and forced-dominant convection regimes. Computational results revealed that the temperature oscillations could be reduced effectively by a proper adjustment of the control parameters. The uniformity of temperature distribution near the crystal rod was examined. The control of oscillatory flow modes was also made for a realistic, low value of Pr.

• Korea-Australia Rheology Journal
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• 제13권2호
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• pp.97-106
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• 2001

Three-dimensional flow analysis was performed by using the control volume finite-element method for design of a profile extrusion die. Because polymer melt behavior is complicated and cross-sectional shape of the profile extrusion die is changing continuously, the fluid flow within the die must be analyzed three-dimensionally. A commercially available polypropylene is used for theoretical and experimental investigations. Material properties are assumed to be constant except for the viscosity. The 5-constant modified Cross model is used for the numerical analysis. A test problem is examined in order to verify the accuracy of the numerical method. Simulations are performed for conditions of three different screw speeds and three different die temperatures. Predicted pressure distribution is compared with the experimental measurements and the results of the previous two-dimensional study. The computational results obtained by using three dimensional CVFEM agree with the experimental measurements and are more accurate than those obtained by using the two-dimensional cross-sectional method. The velocity profiles and the temperature distributions within several cross-sections of the die are given as contour plots.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.612-615
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• 1996

In the continuous casting process, molten metal contacts the mold wall and the molten metal surface is subject to the mold oscillation. The mold oscillation results in the oscillation marks on the surface of solidified steel, which has undesirable effects on the quality of slabs. In order to reduce the oscillation marks by achieving soft contact of molten metal with the mold surface, alternating magnetic field is applied to the surface of molten metal. However, if the magnetic field strength becomes too strong, the melt flow induced by the magnetic field. causes the instability of the molten metal surface, which has also the bad influence on the slab quality. Therefore, it is very important to choose the optimal position of the inductor coil and the optimal level of electric power to minimize the surface defects. In the present work, as a first step toward the optimization problem of the process, numerical studies are performed to investigate the effects of coil position and the electric power level on the meniscus shape and the flow field. As numerical tools, the boundary integral equation method(BIEM) is used for the magnetic field analysis and the finite difference method (FDM) with orthogonal grid generation is used for the flow analysis.

• 대한기계학회논문집A
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• 제21권5호
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• pp.735-745
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• 1997

In this study, the compressibility of resin was considered in filling analysis to account for the possible packing type flow. A numerical simulation program employing a hybrid finite element/finite difference scheme was developed to solve Hele-Shaw flow of the compressible viscous fluid at non-isothermal conditions. To advance the melt front, a control volume approach was adopted. Thin complex 3-D shapes of cavities, runners, and sprues were discretized by employing triangular, cylindrical and/or rectangular strip elements. Mass conservation was applied to each control volume to solve for the pressure distribution. Directly applying a constant mass flow rate at the inlet removes calculation of the apparent pressure boundary conditions, resulting in better simulation condition. The Cross model was used to model viscosity and the Tait equation was employed to represent density as a function of temperature and pressure. The validity of the developed program was verified through comparisons with available data in the literature and the effect of compressibility on the pressure distribution was discussed. To reduce computation time, 1-D and 2-D elements were used instead of applying triangular elements and the numerical results were compared to each other.

• Korea-Australia Rheology Journal
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• 제18권3호
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• pp.153-160
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• 2006

We analyzed the non-Newtonian and non-isothermal flow with Carreau-Yasuda viscosity model in co-rotating and counter-rotating twin screw extruder systems. The mixing performances with respect to the screw speed, the screw pitch, and the rotating direction have been investigated. The dynamics of mixing was studied numerically by tracking the motions of particles. The extent of mixing was characterized in terms of the deformation rate, the residence time distribution, and the average strain. The results showed that the high screw speed decreases the residence time but increases the deformation rate. Small screw pitch increases the residence time. It is concluded that the high screw speed increases the dispersive mixing performance, while the small screw pitch increases the distributive mixing performance. Co-rotating screw extruder has the better conveying performance and the distributive mixing performance than counter-rotating screw extruder with the same screw speed and pitch. Co-rotating screw extruder developed faster transport velocity and it is advantageous the flow characteristics to the mixing that transfers polymer melt from one barrel to the other barrel.

• 반도체디스플레이기술학회지
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• 제12권2호
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• pp.19-25
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• 2013

Extrusion is one of the most important operations in the polymer-processing industry. Balancing the distribution of flow through a die to achieve a uniform velocity distribution is the primary objective and one of the most difficult tasks of extrusion die design. If the manifold in a coat-hanger die is not properly designed, the exit velocity distribution may be not uniform; this can affect the thickness across the width of the die. Yet, no procedure is known to optimize the coat hanger die with respect to an even velocity profile at the exit. While optimizing the exit velocity distribution, the constraint optimization used in this work with allowable pressure drop in the die; according to this constraint we can control the pressure in the die. The computational approach incorporates three-dimensional finite element simulations software STAR-CCM+. These simulations are used with numerical optimization to design polymer coat hanger dies with pressure drop, uniform velocity and temperature variation across the die exit.

• 폴리머
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• 제31권5호
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• pp.399-403
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• 2007

폴리카보네이트/폴리(부틸렌 테레프탈레이트)(PC/PBT) 블렌드에 대해 용융혼합 과정에서 에스테르 교환반응 거동을 조사하였고, PC/PBT 혼합비에 따른 유변학적 특성, 파괴거동 및 파단면 모폴로지를 조사하였다. FT-IR 및 $^1H-NMR$ 분석을 통해 용융혼합 중에 PC와 PBT간 에스테르화 반응이 일어남을 확인하였다. PC 함량이 증가할수록 용융지수(MI)는 감소하여 PC의 높은 흐름저항성을 확인하였다. 또한 PC 함량이 증가할수록 저장 및 손실 탄성률은 증가하였고, Cole-Cole 도시로부터 PC/PBT 블렌드의 경우 혼합비에 관계없이 유변학적 상용성은 나타내지 않은 것으로 나타났다. 인장강도는 PC 함량이 증가함에 따라 선형적인 증가를 나타내었다. 충격강도의 경우 PC 함량이 증가함에 따라 증가하였는데, 약 $30{\sim}40wt%$ 범위에서 가장 급격한 증가폭을 나타내었고, 50 wt% 이상의 범위에서는 거의 일정한 값을 나타내었다. 충격 파단면을 관찰한 결과 약 40 wt% 이상의 범위에서부터 충격방향으로 거친 파괴 릿지(ridge)가 형성되어서 높은 충격강도를 나타낸 것으로 판단된다.

• 대한기계학회논문집A
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• 제30권1호
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• pp.32-41
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• 2006

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder.

• 대한기계학회논문집
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• 제18권7호
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• pp.1818-1832
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• 1994

Transport process during solidification of an AI-CU alloy in a vertical annular mold of which inner wall is cooled is numerically simulated. A model which can take account of local density dependence on the solute concentration is established and incorperated in the analysis. Results show that thermally and solutally induced convections are developed in sequence, so that there is little interaction between them. Thermal convection effectively removes the initial superheat from the melt and vanishes as solidification proceeds from the cooling wall. On the other hand, solutal convection which is developed later over the meshy and the pure liquid regions leads to large-scale redistribution of the consituents. The degree of the initial superheating hardly affects overall solidification behavior except the early stage of the process, when the cooling rate is kept constant. Macrosegregation is reduced remarkably with increasing cooling rate, because not only the liquidus interface advances so quickly that time available for the solute transport is not enough, but also the interdendritic flow is strongly damped by rapid crystal growth within the mushy region.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2003년도 기술심포지움 논문집
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• pp.17-20
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• 2003

The EMC's rheological effects on molding process are evaluated in this study. When considering mold processing for IC packages, the major concerning items in current studies are incomplete fill, severe wire sweeping and paddle shifts etc. To simulate EMC's fast curing rheokinetics with 3D mold flow behavior, one should select appropriate rheometry which characterize each EMC's rheological motion and finding empirical parameters for numerical analysis current studies present the new rheometry with parallel plate rheometry for reactive rheokinetic experiments, the experiment and numerical analysis is done with the commercial higher filler loaded EMC for the case of Thin Quad Plant Packages (TQFP) with package thickness below 1.0 mm. The experimental results and simulation results based on new rheometry matches well in point of the prediction of wire sweep, filling behavior of melt front advancement and void trapping position.