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 dropl et under both terrestrial and microgravity conditions. The numerical model is developed based on the boundary element solution of the electric field d istribution outside the droplet, which is then integrated with the weighted residuals method for determining the droplet shapes that are defined by th e balance of the electrostatic stresses, surface tension, and hydrostatic p ressure when gravity is present. The internal fluid Row and temperature dis tribution 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 pullin g at its two poles. Noticeable Marangoni convection results from all laser heat source arrangements studied. Among these arrangements, the ring heat s ource produces the lowest velocity level and the smallest temperature gradi ent, whereas the highest velocity and greatest temperature difference occur when heating is applied at only one of the poles. For all cases, an increa se in the droplet surface covered by the laser beam helps to reduce the tem perature difference and hence thermally induced Rows in the droplet.