Collision characteristics of neutral and highly charged droplets in uniform electric fields

Abstract

Droplet collision and growth are common phenomena. While charge and electric fields can promote the droplet collision process, the impact of field intensity and high charge on droplet collision characteristics, as in thunderclouds, is not well understood. This paper presents a trajectory model to study the collision characteristics of a neutral droplet and a charged droplet with varying amounts of charge under various electric field intensities. The findings reveal a transition stage in collision efficiency as the electric field E increases, related to droplet size variation. During this transition stage (about E = 7.5 × 102 V⋅m−1 to 7.5 × 104 V⋅m−1), there is a peak in the collision efficiency of highly charged and neutral droplets as the neutral droplet size increases. Conversely, at other electric fields (near 102 V⋅m−1 and between 7.5 × 104 V⋅m−1 and 107 V⋅m−1), a larger neutral droplet is advantageous for enhancing the collision efficiency, increasing the collision probability. Throughout the range from 102 V⋅m−1 to 107 V⋅m−1, a larger neutral droplet is beneficial for enhancing the collision kernel, raising the collision frequency. An increase in charge significantly enhances both collision efficiency and kernel. For a micrometer-sized charged-neutral droplet pair, collision efficiency initially decreases (disturbance effect) and then slightly rises to about 1.0 (inertial effect) with the electric field at a constant droplet size ratio. In addition, the impact of droplet size on collision characteristics was investigated, and the collision characteristics of two neutral droplets were compared. The results deepen our understanding of the internal physical processes of cloud droplet collisions under varying electric fields and charge conditions (especially high charges) and provide guidance for applications like electrostatic defogging, charged particle catalyzed rainfall, and fog collection.