Condensation dynamics on inclined heterogeneous substrates

This study presents numerical simulations of dropwise condensation on inclined chemically heterogeneous substrates in pure vapor atmosphere. To capture the dynamics of this process, a one-sided condensation model with a disjoining pressure is employed that incorporates the effects of gravity and chemical heterogeneities. We consider surfaces decorated with an array of square patches which are more hydrophilic compared to the rest of the surface, which act as nucleation, inception regions over which droplets form and grow and ultimately depin once their size becomes sufficiently large. The impact of the size and of the inception regions and the angle of inclination on the dynamics is considered, revealing significant qualitative and quantitative differences between the cases. For cases with purely structured substrates, it is observed that, as the number of inception regions increases, the condensation process transitions from steady to unsteady, with the critical number of inception regions increasing with the inclination angle increases. Further insight is provided by analyzing the snapshots of the liquid phase on the substrate, revealing the formation of liquid streaks or films, which influence both the dynamics of the flow and the total liquid volume on the substrate. The inclusion of random impurities on the structured substrate dramatically impacts the condensation dynamics, which is found to hinder the formation of liquid film, leading to a decrease in the total liquid volume generated on the substrate.