The Dynamic Contact Angle of Water Droplets Subjected to AC Electric Fields

The acoustic impact of corona discharge from high voltage (HV) conductors is a cause of increasing environmental concern. Excessive corona discharge is initiated under wet weather when a large amount of droplet protrusions is formed on the surface of an HV conductor. The surface condition of the conductor therefore significantly affects the inception, development and intensification of corona discharges through electrohydrodynamic processes. Existing studies on the dynamic characteristics of rain droplets assumes a constant contact angle, which does not conform with the actual profile observed in experiments. This article investigates the dynamic contact angles of charged droplets through a simplified sphere-plane HV experiment. Pendent droplets with a range of sizes have been studied when subjected to AC electric fields. It is found that the variation of dynamic contact angle is closely related to the volume of the water droplet. Clear sinusoidal variation of contact angle with time is seen throughout the whole power cycle for larger droplets $(\ge 6 \mu \text{L})$, while variation is smaller and more difficult to categorize on the smaller droplets $(\lt 6 \mu \text{L})$. The characteristics of dynamic contact angle obtained here can be used for further analysis within the finite element method to investigate its electrohydrodynamic properties.