Title: Numerical study of three-dimensional mixed convection due to buoyancy and centrifugal force in an oxide melt for Czochralski growth
Authors: Enger, Sven
Basu, Biswajit
Breuer, Michael  
Durst, Franz
Language: eng
Issue Date: 2000
Publisher: Elsevier
Document Type: Article
Source: In: Journal of crystal growth. - Amsterdam [u.a.] : Elsevier, ISSN 0022-0248, ZDB-ID 3043-0 - Bd. 219.2000, 1, S. 144-164, insges. 21 S.
Journal / Series / Working Paper (HSU): Journal of Crystal Growth
Volume: 219
Issue: 1
Page Start: 144
Page End: 164
Publisher Place: Amsterdam
Mixed convection due to buoyant and centrifugal forces in the crucible of a Czochralski apparatus has a significant effect on the quality and stability of growing oxide single crystals. Thus, the present investigation is concerned with the time-dependent and three-dimensional simulation of the flow and heat transfer in an oxide melt with a rotating crystal for a fundamental understanding of mixed convection and its effect on the surface waves. Based on an efficient block-structured finite-volume Navier-Stokes solver, quasi-direct numerical simulations (quasi-DNS) were carried out. A cylindrical crucible filled with a high Prandtl number (Pr = 10.45) model fluid was considered for different combinations of Rayleigh numbers (Ra = 4.0×108 and 7.6×10s) and Reynolds numbers (Re = 235-461). It was found that the surface wave pattern is strongly dependent on the structure of the three-dimensional and time-dependent fluid flow in the crucible. For all cases predicted, the waves exhibit regularity and the flow structure is fully symmetric in the vertical midplane as long as the centrifugal force has a significant effect on the flow below the disc. Furthermore, a downward buoyant jet was found to form at the disc center in all cases when the upper flow column due to the centrifugal force becomes restricted to the top. The transient flow development can be characterized by Gr/Re2. For Gr/Re2 = 235 the flow field is always periodic whereas it attains a non-periodic state through a number of quasi-periodic modes for Gr/Re2 larger than 334. Increasing values of Gr/Re2 lead to an earlier onset of the non-periodicity. Except during the initial period, the hot fluid is pushed below the disc primarily by the radial buoyant convection. This hot fluid interacts with the cold column of the downward buoyant flow controlling the temperature at the crystal/melt interface. The shape, the rotation rate of the waves, and the transient nature of the flow field were found to be in agreement with experimental observations. © 2000 Elsevier Science B.V. All rights reserved.
Organization Units (connected with the publication): Universität Erlangen-Nürnberg
ISSN: 00220248
Publisher DOI: 10.1016/S0022-0248(00)00592-3
Appears in Collections:Publications of the HSU Researchers (before HSU)

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