Evaporation Characteristics and Heat Transfer Enhancement of Sessile Droplets under Non-uniform Electric Field

Abstract Electrohydrodynamic (EHD) enhancement of water droplet evaporation by non-uniform electric field and the subsequent dynamic characteristics were experimentally investigated in this paper. A pin-to-plate electric field was produced by a needle connected to a high-voltage power supply and the grounded heated surface coated by thin Teflon film with a contact angle of about 100°. The droplet was generated onto the hot surface by a micro-syringe with a constant initial volume of 4 μl, and a high-speed camera was used to capture the droplet morphology. Effects of electric field and surface temperature on the contact angle, droplet height, evaporation stage, volume variation, and evaporation rate were studied. The results showed that both the increase in external electric field strength and surface temperature enhance droplet evaporation with a maximum enhancement ratio of 6.8 times in the present work. In addition, a special extra constant contact angle (CCA) stage was found in droplet evaporation under electric field, while only constant contact radium (CCR) and Mixed stages existed in neutral (no voltage) evaporation. In particular, the evaporation enhancing mechanism of no-uniform electric field considering corona wind blowing, surface tension weakening and molecular orientational alignment was also presented.