Flow modelling with relevance to vertical gradient freeze crystal growth under the influence of a travelling magnetic field

Results on the experimental and numerical modelling of the melt flow typically observed in vertical gradient freeze (VGF) crystal growth with a travelling magnetic field (TMF) are presented. Particular attention is paid on the transition from a laminar to a time-dependent flow, which represents a crucial problem in VGF growth. Low-temperature model experiments at around 80 °C were performed using a GaInSn melt in a resistance furnace with concentric, separately adjustable heating zones. The TMF was created by an external coil system, and the flow velocity was measured by means of the ultrasonic Doppler velocimetry (UDV). The melt flow was simulated numerically using a finite volume code based on the open source code library OpenFOAM. As a criterion for the stability of the flow the turbulent kinetic energy was calculated under the influence of the TMF and thermal buoyancy. The results obtained are compared to isothermal TMF flow modelling at ambient temperature. The stability limit of the melt flow is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. Both experimental and numerical results show the stabilizing effect of natural, VGF-type buoyancy on the TMF-induced flow.