Atomization Prediction Model on Superhydrophobic Surfaces*

When a drop impinges a superheated surface intense atomization can occur. Atomization intensity varies as a function of time, Weber number, and surface temperature; it is also a strong function of surface characteristics. This study considers dynamic atomization on both hydrophobic and superhydrophobic surfaces (SH). SH surfaces are coated with a hydrophobic coating and micro-scale pillars. This work presents an analytical model, based on thermal transport and impingement flow dynamics, that predicts the amount of vaporization that occurs when a drop impacts a SH surface. The model accounts for pitch and solid fraction, surface temperature, and We number. Vapor generation is calculated from the model, and the results correlate well with experimentally measured amounts of atomization on the same surfaces. The results show a variation of vapor production with surface superheat. Vapor production increases with increasing temperature until it reaches transition boiling and then decreases until the Leidenfrost point. The results also show vapor production varies strongly with solid fraction and pitch. A maximum in atomization intensity is observed on a SH surface with 8 µm pitch and solid fraction of 10% at a surface temperature of 280.