Behaviors of microdroplets impinging on supercooled superhydrophobic microgrooves

Microdroplet impact icing is a common occurrence in high altitudes or cloud environments. There is a lack of in-depth understanding regarding the icing behaviors of microdroplets interacting with anti-icing microstructures. While the impact of microstructure pitch on delaying icing is extensively studied, the microstructure height, as a similarly technology-controllable structural parameter, has received comparatively little attention in research. This study investigates the impact dynamics of microdroplets on supercooled superhydrophobic microgrooves, utilizing the coupled level-set and volume of fluid and enthalpy-porosity technologies for precise simulation. The behaviors of microdroplets impact on supercooled surface manifest distinctive characteristics compared with ambient surface, particularly evident when We < 170 (βmax (maximum spreading diameter)/βMod (predicted spreading diameter) ∼ 0.8). Unlike flat surfaces, microgrooves have been shown to reduce βmax by 52%. Additionally, an increase in H/Do (ratio of microgroove height H and droplet diameter Do) leads to a diminishing trend in βmax, showing a reduction of 13%. The outcomes of microdroplet impact progress from complete bouncing, partial bouncing, bouncing with satellite droplet breakup, to deposition, sequentially as the We and surface supercooling degree escalate. Heightening the microstructure alters the transition point between partial bouncing and bouncing with breakup, thereby expanding the range of droplet bouncing (with thresholds being doubled). This effect is attributed to satellite droplet breakup, supported by simulation results suggesting that droplet breakup reduces interface curvature, thus facilitating bouncing. Moreover, microgroove structures have the potential to decrease the dimensionless contact time of droplets by 33% when comparing H/Do = 0.4 with H/Do = 0.1.