The effect of flow regime on surface oscillations during electromagnetic levitation experiments

Abstract

During containerless processing, the oscillating drop method can be used to measure the surface tension and viscosity of a levitated melt. Through containerless processing, reactive melts that cannot be measured through conventional methods can be accurately measured; however, the accuracy of this method is dependent on the internal flow within the drop. While laminar flow does not redistribute the momentum of the oscillations, turbulent flow does redistribute the momentum of the flow and, as a result, dominates the damping. As a result, it is important to understand the internal flow behavior and the factors that affect the flow during these experiments. Models are used for the indirect quantification and characterization of the internal flow using the experimental parameters and material properties. In some cases, such as Cu50Zr50, the flow is laminar over the full range of the experiment. In other cases, including Al75Ni25, the sample is dominated by turbulent flow at high temperatures and applied electromagnetic fields, but upon cooling, transitions to laminar flow. Additionally, cases exist in which the flow is fully turbulent over the range of interest and valid measurements using the oscillating drop method are not possible. During the design phase of the experiment, the experimental parameters should be modeled to characterize the flow behavior and ensure a clean experiment.

Demonstration of the effect of stirring on nucleation from experiments on the International Space Station using the ISS-EML facility

“…The fluid flow velocities and shear rates corresponding to each positioner and heater voltage settings were simulated following procedures described in refs. [37,38] and in the supplemental section. The fluid flow velocities and shear rates usually show a distribution, which evolves with decreasing temperatures, being largest near the poles and smallest near the equator of the sample due to the distribution of the rf-field along the sample geometry.…”

“…The voltages and currents applied to the positioner and heater coils, their frequencies, the position and diameter of the sample with respect to the coils, sample electrical resistivity and coupling coefficient to the rf fields, the liquid viscosity and density as a function of temperature are the input parameters in this model. 37,38 The particular details of the coil geometry and the rf fields can be found elesewhere. 39 The temperature dependent viscosities of the liquids were measured by a ground-based electrostatic levitation facility 40,41 at Washington University in St. Louis and were reported earlier.…”

Examining the influence of turbulence on viscosity measurements of molten germanium under reduced gravity

“…During turbulent flow, the momentum of the surface oscillations is redistributed by the turbulent eddies and damping is dominated by the turbulent dissipation rather than by the inherent viscosity of the liquid. As a result, it is important to calculate the Reynolds number describing the flow within the drop 14 , 15 .…”

Thermodynamic assessment of evaporation during molten steel testing onboard the International Space Station

“…This powerful containerless technique simultaneously allows researchers to levitate and thermally condition molten metal droplets providing the advantage of processing samples without adverse impacts related to sedimentation, chemical reactions, or heterogeneous nucleation on crucible walls. The extended period of microgravity environment also enables the opportunity to conduct long duration experiments in the undercooled regime under a wide range of controlled flow conditions 17,18,19 . Fig.…”