Status of Viscosity Measurements by the Oscillating Drop Method in an Electromagnetic Levitation Device under Reduced Gravity Conditions

The oscillating drop method in an electromagnetic levitation device under reduced gravity conditions has found wide applications for surface tension and viscosity measurements of high temperature reactive metallic alloys. Microgravity conditions are required because under 1-g conditions the strong levitation fields cause turbulent fluid flow which impedes the evaluation of the viscosity from the measured damping time constant of the surface oscillations. Magnetohyrodynamic modelling predicted a dependence of the damping time constant on the amplitude of the surface oscillations and on the residual positioning field. For a verification of these results a series of experiments on parabolic flights and on a TEXUS sounding were performed. The results indicate an effect of the initial surface oscillation amplitude and an effect of the positioning field on the damping time constant. From these findings limiting values of control parameters for the application of the oscillating drop method in an emlevitation can be set.