Comparison and a Possible Source of Disagreement between Experimental and Numerical Results in a Czochralski Model

• Published in: Fluid dynamics & materials processing Vol. 9; no. 3; pp. 209 - 234
• Main Authors: Haslavsky, V, Miroshnichenko, E, Kit, E, Gelfgat, A Yu
• Format: Journal Article
• Language: English
• Published: Duluth Tech Science Press 01.01.2013
• Subjects: Amplitudes; Computer simulation; Crystals; Czochralski process; Destabilization; Dummies; Excitation; Flow stability; Free surfaces; Instability; Mathematical models; Numerical prediction; Oscillations; Rotation; Stability; Temperature gradients
• ISSN: 1555-256X; 1555-2578
• DOI: 10.3970/fdmp.2013.009.209

Experimental and numerical observations of oscillatory instability of melt flow in a Czochralski model are compared, and a disagreement observed at small crystal dummy rotation rates is addressed. To exclude uncertainties connected with flow along the free surface, the latter is covered by a no-slip thermally insulating ring. Experiments reveal an appearance of oscillations at temperature differences smaller than the numerically predicted critical ones. At the same time, a steep increase of the oscillations amplitude is observed just beyond the computed threshold values. By increasing the dummy rotation gradually, we are able to qualitatively confirm the numerically predicted flow destabilization. A good quantitative comparison is reached only with a rather strong rotation of the crystal dummy. Focusing on the disagreement in the non-rotating case, we argue that the experimentally observed instability is triggered by an external excitation that results from low-amplitude temperature oscillations in thermostatic baths. This argument is supported by a numerical simulation of the parametrically excited model.