EHD enhancement of boiling heat transfer of R123 inside a vertical tube concentric with a cylindrical electrode was tested. These experiments demonstrated that the strength of applied electric field had an optimum value，under which the highest enhancements of boiling heat transfer took place at a lower heat flux and that the factors of heat transfer enhancement for a lower heat flux was larger than those for higher one. It was found that electric current increased as applied electric field strength increased and decreased as heat flux increased and that breakdown strengths of electric field fell as heat flux increased. The mechanisms of EHD enhancement of boiling heat transfer inside a vertical tube were analyzed and discussed on the view of the effect of electric field on growth rate

departure and movement behavior of bubbles.