Modelling of electromagnetic levitation - Consequences on non-contact physical properties measurements

Abstract

Electromagnetic lévitation of electrically conductive droplets by alternating magnetic fields is a technique used to determine the physical properties of liquid metallic alloys such as surface tension, viscosity, heat capacity and thermal diffusivity/1/. To improve accuracy, it is mandatory to reduce electromagnetic stirring and shaping of the droplet, therefore experiments are conducted in microgravity. Properties are deduced from direct measurements of position or temperature using specific models. Our purpose is to check various assumptions on which those models are built by the use of adapted numerical codes. We first compare experimental and numerical results concerning the shape and mass centre oscillation frequencies of electromagnetically levitated Nickel droplets. Axisymmetric numerical model yields equilibrium shapes and positions of the droplets in a good agreement with experiment. Then, fluid flow effects on the measurement precision of surface tension and viscosity by comparing expected and calculated properties values are characterized. We determine critical values of initial droplet distortion or magnetic field intensity which can lead to an overestimate of the value of viscosity. We also calculate flow effects on heat capacity and thermal conductivity values.