Effects of particle’s surface properties and aggregation modes on water vapor competition in heterogeneous nucleation of water vapor on the particles

Abstract

Heterogeneous nucleation of water vapor on particles to promote particulate abatement is widely used in the fields of industrial dust removal pretreatment technology. Water vapor competition is a very important phenomenon in the process of particles nucleation, but due to the limitations of experimental methods, this phenomenon is difficult to observe and rarely received attention. Therefore, in order to reveal the influence of water vapor competition on particles nucleation, a direct visualization method based on the Environmental Scanning Electron Microscope (ESEM) is proposed in this work to obtain the water vapor competition process during particles nucleation at a microscopic scale. Firstly the effect of particle’s surface structure on water vapor competition in heterogeneous nucleation of water vapor on the particles is visualized by the ESEM. The results show that the embryo appears randomly at any edge of the smooth spherical particle because water vapor competition at each point on the particle’s surface is equal. While the embryo always appears on the protuberance of the convex spherical particle since water vapor competition is strongest there. Then the influence of particle’s surface energy on water vapor competition is also visualized. Water vapor preferentially nucleates on the particle with smaller contact angle, which means the higher the surface energy, the more conducive it is for water vapor competition to form embryos. Finally, the impact of particle’s aggregation modes on water vapor competition is also visualized by the ESEM. The results show that when the vapor supersaturation is constant, water vapor only nucleates on the two-close and three-circled particles while particles nucleation on the single particle is never observed. This is due to the strong water vapor competition at the particle’s junction, where the embryos will collide and coalesce to form an embryo larger than the critical size to activate particles nucleation. The results of this study will deepen the microscopic understanding of water vapor competition in the process of particles nucleation.