Suppression of temperature oscillation in Czochralski convection by superimposing rotating flows

Abstract

A numerical study was made of a control technique of transient oscillatory flows in Czochralski convection. The suppression of temperature oscillation was achieved by changing the rotation rate of crystal rod Omega = Omega(0)(1 + A(S) sin(2 pi/t(p)f(S)t)), where A(S) denotes the dimensionless rotation amplitude and f(S) the frequency. Based on the inherent oscillatory time period of the melt (t(p)), the suppression rate of temperature oscillation was characterized by the mixed convection parameter Ra/(Pr Re-2). This parameter ranged in the study 0.225 less than or equal to Ra/(Pr Re-2) less than or equal to 0.929, which encompasses the buoyancy- and forced-convection dominant regimes. Computational results revealed that the temperature oscillation can be suppressed significantly by adjusting the control parameters. The uniformity of temperature distribution in space and in time near the crystal interface was scrutinized. Copyright (C) 1996 Elsevier Science Ltd.