Vapor condensation heat transfer on mixed-wettability surface with lattice Boltzmann model

Based on an improved three-dimensional phase-change lattice Boltzmann method (LBM), this study conducts three-dimensional numerical simulations for vapor condensation heat transfer on the mixed wettability surface consisting of a hydrophobic substrate decorated by the hydrophilic regions. Droplet nucleation, growth and detachment from such surface are discussed in detail, with regarding the parametric effects of the shape, size and spacing of the hydrophilic regions, as well as contact angles of both the hydrophilic and hydrophobic regions. Results show that the hydrophilic regions with identical area but different shapes lead to minor differences in heat transfer performance. However, the regions with equal perimeter but various shapes can result in significant differences. The size of the hydrophilic region is a key factor affecting droplet nucleation, and a larger hydrophilic region can increase the surface heat flux and enable earlier droplet detachment. Besides, a smaller spacing between hydrophilic regions promotes droplet formation, despite the fact that an excessively small spacing inhibits droplet detachment. The contact angles of both hydrophilic and hydrophobic regions can affect droplet formation, with the former influencing early-stage formation and the latter impacting later-stage growth. This study further improves the understanding of the mixed wettability surfaces used in the vapor condensation scenario from the numerical view.