• 대한기계학회논문집B
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• 제21권3호
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• pp.445-456
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• 1997

Continuous casting process is numerically analyzed using the continuum model in a non-orthogonal coordinate system. Flow damping in the mush is modeled by combining the viscosity dependence on liquid fraction in dilute mush and the permeability dependence on liquid fraction in concentrated mush. The effect of turbulence is indirectly considered by effective diffusivity determined elsewhere by experiment. The main objective is to investigate the effects of casting parameters such as casting speed and tundish superheat on the distribution of surface temperature, shell thickness, metallurgical length and centerline segregation. Some of the computed results are compared with available experiments, and reasonable agreements are obtained.

• 대한기계학회논문집B
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• 제21권4호
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• pp.525-540
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• 1997

The effect of mold rotation on the transport process and resultant macrosegregation pattern during solidification of an Al-Cu alloy contained in a vertical axisymmetric annular mold cooled from the inner wall is numerically investigated. The mold initially at rest starts to rotate at a prescribed angular velocity simultaneously with the beginning of cooling. Computed results for a representative case show that the mold rotation essentially suppresses the development of both thermal and solutal convections in the melt, creating distinct characteristics such as the liquidus front, flow pattern and temperature distribution from those for the stationary mold. Thermal convection which develops at the early stages of cooling is soon extinguished by the rotating flow induced during spin-up, and thus does not effectively remove the initial superheat from the melt. On the other hand, solutal convection, though it weakens considerably and is confined within the mushy zone, still predominates over the solute redistribution process. With increasing the angular velocity, the solute transport in the axial direction is enhanced, whereas that in the radial direction is reduced. The final macrosegregation formed in the mold rotating at moderate angular velocities appears to be favorable in comparison with the stationary casting, in that not only relatively homogenized composition is achieved, but also a severely positive-segregated channel is restrained.

• 대한기계학회논문집
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• 제17권1호
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• pp.162-171
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• 1993

본 연구에서는 2성분혼합물의 응고과정해석에 머시영역의 비등방성을 포함시 킬수 있는 모델을 정립하고 실제계산을 수행하여 비등방성이 천이현상 및 조대편석(m- acrosegregation)에 미치는 영향을 보이고자 한다. 이 과정에서 기본 방정식의 변형 을 통한 수치해석의 효율화에 관해서도 취급할 것이다. 해석대상은 비등방성의 효과 가 잘 나타날 수 있으면서 해석은 용이한 2차원 정사각형용기로 선택하였다. 대상혼 합물은 실용적으로 관심있는 금속 합금과 결정구조가 유사하며 물성치가 비교적 잘 확 립된 염화암모늄수용액(NH$_{4}$C1-H$_{2}$O)이다. 특히 아공정염화암모늄수용액은 부력비(buoyancy factor)가 -1.4정도로서 온도와 농도구배에 의한 부력이 크기는 비슷 하지만 작용방향이 반대이기 때문에 이중확산대류의 전형적인 형태를 고찰하기에 편리 한 물질이다.