Effect of convection on the measurement of thermophysical properties using levitated droplets

This article discusses the recirculating convection in free droplets levitated by either the electromagnetic forces or the electrostatic forces, and its effect on the measurement of thermophysical properties. In an electromagnetically levitated droplet, strong internal flow results from the vortical Lorentz forces induced by the surrounding coils. These forces are also responsible for free surface deformation. In an electrostatically levitated droplet, however, internal convection originates from the thermal gradient and the electrostatic forces are responsible for surface deformation only. Mathematical models for predicting the convection in these droplets and the surface deformations caused by either the electromagnetic or electrostatic forces are discussed. Results show that internal convection, when present, can have a significant effect on the measured data for the purpose of determining the thermophysical properties. The deformed surface assumes essentially the same oval shape in microgravity for both electromagnetically and electrostatically levitated drops. The deformation mechanism, however, is different. Future research directions in this area are also discussed.