Nucleation of water vapor on nanodimpled surfaces: Effects of curvature radius and surface wettability

Abstract

• The effects of dimple curvature radius and wettability on nucleation are studied. • Surface potential energy analysis confirms nucleation sites. • Increasing dimple curvature radius worsens nucleation. • More dimples increase vapor nucleation probability at lower surface subcooling. • The coupling effect of the surface structure affects the nucleation. The mechanisms of vapor nucleation on nanostructured surfaces, whose geometrical characteristic sizes are comparable to those of nuclei, remain unsatisfactorily explored. This study investigates the correlations among the wettability, dimple curvature radius, and nucleation characteristics of vapor molecules on nanodimpled surfaces through molecular dynamics simulations. The surface potential energy analysis demonstrates that nucleation sites are located in the interior of dimples. With an increase in surface hydrophobicity or dimple curvature radius, a higher nucleation energy barrier would render nucleation more difficult. The critical sizes of nuclei obtained from MD simulation are larger than the results estimated by the classical nucleation theory. The discrepancy is attributed to the fact that the formed nucleus in simulations deviates from the spherical cap assumption. The formation of nuclei is not observed at all dimples, indicating that the coupling effects of surface structure would affect nucleation. Additionally, the comparisons of coalescence phenomena noted for different dimple numbers reveal the benefits of increasing the dimple number, which can be attributed to the fact that more high-energy nucleation sites increase the nucleation probability of vapor molecules at reduced surface subcooling. Therefore, an enhanced condensation performance can be achieved by artificially controlling the dimple number.