Combined effect of charges and external electric field on collision-coalescence of microns and nanoscale droplets: A numerical simulation perspective

Abstract Corona discharge is gradually attracting attention in catalyzed artificial rainfall due to its high efficiency and simplicity. Considerable researches focus on the macro phenomena, such as the increase of rainfall probability in statistics, and the observation of large particle size generation. However, due to the complexity of solving space charges, electric field and phenomena induced by corona discharge, relevant research on the micro mechanism is deficient, especially for the collision-coalescence of droplets with a diameter from nano-sized to micron-sized under the effect of charges and electric field. In this paper, systematic numerical simulations are conducted to study the coalescence between micron-sized droplets by phase field method, and coalescence time is introduced to characterize the speed of coalescence. In addition, “charged particle tracking” module is used to study the collision and coalescence between micron-sized droplet and nano-sized droplet, and collision efficiency is used as the evaluation index. The evolution of charged droplets under different conditions are discussed in detail in this paper, and results demonstrate the significant combined effect on the collision-coalescence process of charges and external electric field. The research results are conducive to reveal the micro-mechanism of the coagulation of macro droplets induced by corona discharge to some extent, and also provide a guidance for optimizing the water-collecting device by improving the speed and efficiency of droplet coalescence.