Forces and charge analysis of a water droplet dragged by an electric field

Abstract

Droplet removal from solid surfaces is particularly important for heat and mass transfer, corrosion protection, and certain technological requirements in production. In this study, we investigate droplet removal from a solid surface using an electric field. First, a visual platform was established to capture a video of the droplet deforming and jumping motion in an electric field, and a deformed ellipse equation was applied to fit the liquid droplet profiles. Second, the electric charge distribution was obtained, and the electric forces on the droplet surface before and after jumping were calculated. The result indicates that the charge only accumulates on the upper surface of the droplet, mostly at the top point, and the maximum charge of the 7  μl droplet is about 2 × 10−4  μC in this experiment. The forces on the droplet are almost constant and maintain a constant acceleration (greater than 10 m/s2) after leaving the surface. Third, the effects of droplet volume, electric field intensity, and electrode plate distance on droplet jumping were quantitatively studied. The experiments show that the electric field intensity required for droplet jumping is independent of the droplet volume but positive with the distance between the plates, when the distance between plates increases from 10 to 18 mm, the critical jumping electric field intensity increases by 0.1 kV/mm. The droplet acceleration decreases by about 20% with the increase in volume (5–10  μl) but increases with the increase in electric field intensity. The charge increases with the increase in electric field intensity, but the charge–mass ratio decreases by about 30% with the increase in volume (5–10  μl). Finally, the results show that a small volume and plate distance are more favorable to stimulating the droplets jumping under the electric field.