Effects of Heat Source Arrangements on Marangoni Convection in Electrostatically Levitated Droplets

A numerical study is presented of surface deformation, Marangoni convection, and temperature distribution in an electrostatically levitated melt droplet under both terrestrial and microgravity conditions. The numerical model is developed based on the boundary element solution of the electric field distribution outside the droplet, which is then integrated with the weighted residuals method for determining the droplet shapes that are defined by the balance of the electrostatic stresses, surface tension, and hydrostatic pressure when gravity is present. The internal fluid flow and temperature distribution in the electrostatically deformed droplet are computed using the finite element method. Computed results show that the electrostatic normal stresses induced by the applied electric field deform the droplet by pulling at its two poles. Noticeable Marangoni convection results from all laser heat source arrangements studied. Among these arrangements, the ring heat source produces the lowest velocity level and the smallest temperature gradient, whereas the highest velocity and greatest temperature difference occur when heating is applied at only one of the poles