Visualization and numerical investigations on heterogeneous nucleation of water vapor on the surface of SiO2, Fe2O3 and CaSO4 particles

Abstract

Particles composition has an important influence on heterogeneous nucleation of water vapor on the particles surface and subsequent particles abatement by heterogeneous condensation. In this work, three kinds of single-component particles of typical chemical composition of coal-fired fine particles are selected. First, Environmental Scanning Electron Microscopy (ESEM) system is adopted to directly visualize the heterogeneous condensation process of water vapor on the particles surface. It can be found that when water vapor condenses on the particles, spherical cap-shaped embryo droplets occur, which is significantly consistent with the embryo model theory proposed by Fletcher (1958). Then, according to Fletcher’s nucleation theory, a numerical experimental platform is established by MATLAB programming to predict nucleation parameters. The theoretical critical supersaturation and the experimental results are compared at the same time. It is noted that the classical theory of heterogeneous nucleation underestimates particles nucleation ability and predicts a higher critical supersaturation than that experimentally measured. Finally, the growth rate of droplets on three kinds of particles is obtained experimentally. The results show that with the same initial particle size, the final growth size of CaSO4 is larger than that of SiO2 and Fe2O3 particle, and the growth rate of droplets on CaSO4 is also the largest, showing the best growth performance.Copyright © 2022 American Association for Aerosol Research