Dual-plane flow mapping in a liquid-metal model experiment with a square melt in a traveling magnetic field

Directional solidification is an important process for fabricating large multicrystalline silicon ingots. The complex 3D melt flows during solidification can be influenced by magnetic fields and are usually investigated in model experiments using 1D ultrasound Doppler measurements and extensive sensor traversing. We present a dual-plane, two-component ultrasound array Doppler velocimeter that utilizes four ultrasound line arrays for flow measurements in liquid metals at room temperature that achieves high temporal and spatial resolution at the same time. It was successfully applied to isothermal model experiments in square-shaped containers under the influence of a vertically traveling magnetic field. Depending on the aspect ratio of the melt different 3D flows were observed: With lower melt heights, a central horizontal vortex appears, while higher melt heights lead to a toroidal flow structure, which is similar to the structure in cylindrical container geometries. Corresponding numerical simulations showed a good qualitative agreement with the measurement data.