Lagrangian Modeling of Dropwise Evaporation in a Shear Driven Flow Over Super Hydrophilic and Super Hydrophobic Surfaces

The impinging droplets and runback water evaporation process triggered by anti-icing devices for in-flight icing protection are considered: a stream of supercooled small droplets impinges on a surface heated from below, to prevent ice accretion. The industry standard, for the simulation of in-flight icing, assumes continuous water film and neglects the effects of wettability properties of the surface. Here, to assess the anti-icing performance enhancement offered by modern super hydro-phobic or low-ice adhesion coatings, an alternative approach is described. The evolution of each single droplet impinging on the surface is traced following a Lagrangian approach. A set of phenomenological rules and models defines the coalescence process, the threshold radii for the transition from static to moving droplets and from moving droplets to rivulets, as well as the heat transfer within the single droplet. Heat and mass transfer balances control the phase change. The model is validated against literature experimental data, showing its ability to capture the qualitatively different ice topology accreted on surfaces of different wettability performances. Results confirm that super-hydrophobicity does not provide full passive icing protection.