2003 Fiscal Year Final Research Report Summary
Oscillatory Thermal Convection and its Three-Dimensional Structure in a Cylindrical Cavity Filled with Liquid Metal.
| Project/Area Number |
14550204
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thermal engineering
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| Research Institution | College of Industrial Technology |
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Principal Investigator |
WAKITANI Shunichi College of Industrial Technology, Department of Mechanical Engineering, Professor, 機械工学科, 教授 (80108125)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Natural Convection / Czochralski echnique / Low Prandtl Number / Liquid Metal / Oscillatory Flow / Numerical Simulation |
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| Research Abstract |
Thermal convection in a cylindrical cavity, as a model of a crucible in Czochralski crystal growth process, has been studied numerically and experimentally. The sidewall and bottom of the cavity are maintained at a uniform high temperature. The melt surface is in contact with a rod as a growing single crystal, and the solid/melt interface is maintained at a uniform low temperature.
Convective oscillations, which appear in low Prandtl number (Pr) fluids, cause undesirable structure of growing crystals called as 'striations.' It is the aim of this study to clarify the convective structure.
Numerical calculations are carried out for the aspect ratio of the cavity, Ar=2, the radius ratio, Rr=0.3 and 0.5, Pr=0.025, and various Grashof numbers under the conditions, a) without heat loss on the melt surface (adiabatic) and without rotation of the rod, b) without heat loss and with rotation of the rod, and c) with heat loss and with rotation of the rod. The results are as follows.
1. When the natural convection dominates in comparison with the forced convection due to rotation of the rod, the flow structure consists of a single toroidal roll with descending flow in the vicinity of the central axis and ascending flow along the cavity wall.
2. The toroidal roll is rotationally symmetric with an azimuthal wavenumber of 3 or 4.
3. As the rotation rate is increased, a rotating flow appears with phase speed of azimuthal wavenumber of 3.
The experiments conducted using Gallium for Ar=2 and Rr=0.5 shows the following results.
1. When the natural convection dominates, critical Grashof number, at which oscillation occurs, decreases with increasing rotation of the rod.
2. When the forced convection dominates, the rotation of the rod generally shows a tendency to suppress oscillations.
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