Bifurcation analysis of liquid films over low wettability surfaces

Thin liquid layer evolution over a solid substrate and film instability phenomena are involved in a number of engineering applications: in chemical absorption through structured packing, the corrugated sheets are covered by the liquid solvent, offering an enhanced interface surface between the solvent and the gas solute; in coating process, the liquid pattern influences the resulting coating quality; in condensation over finned dehumidifier, heat transfer performances are influenced by the evolving liquid layer, which may arrange as a droplets population or an ensemble of rivulets. Here, the evolution of a liquid layer flowing down an inclined plate bounded by lateral walls, which is the simplest configuration describing hydrodynamics inside structured packing, is numerically investigated. An in-house code, previously developed and largely validated in case of film instability and rivulet buildup, is used in order to solve governing lubrication equations. The full implementation of capillary pressure allows to simulate contact angles up to 60 . Film break is observed due to instability induced by lateral walls, if the imposed liquid flow rate exceeds a critical value, leading to the formation of a rivulet pattern. Fixing the size of the investigated physical domain, the number of observed rivulets, which strongly influences the resulting wetted area, is traced as a function of the flow characteristics (identified by the Bond number), the substrate wettability and the liquid properties; the corresponding bifurcation diagram is presented.