Droplet impact on inclined substrates under a non-uniform electric field

Droplet impact on inclined substrates under electric fields is a common behavior in electrostatic demisting applications, and understanding the droplet dynamics of this process is important for improving the performance of demisters. This study investigated the droplet impact dynamics on inclined substrates within a non-uniform electric field. Using high-speed imaging, the effects of voltage (U), substrate inclination (theta), and impact velocity (v) on the droplet behaviors were analyzed. The results revealed that at higher voltages, an upward ejection or pinch-off from the liquid column occurred during the recoiling stage, while the maximum dimensionless spreading diameter D-max* increased with the voltage up to U <= 12 kV, then sharply decreased due to the droplet ejection for U > 12 kV. It was found that the electric field also intensified the droplet oscillation, with the maximum recoiling height H-max* positively correlated with U. The secondary droplet ejection volume fraction eta increased with the increase in U, decreased with the increase in both theta and D-0, and peaked at v = 0.77 m/s. Furthermore, a critical threshold for the ejection or pinch-off and a predictive model for D-max* were developed, incorporating electric Bond number (Bo(E)), Weber number (We), and theta. Based on a profound comprehension of the electrohydrodynamic mechanisms governing the droplet impact on inclined substrates, these findings provide appropriate operating conditions to avoid the droplet pinch-off and ejection, improving the efficiency of electrostatic demisters.