Effect of gas flow rate on bubble formation on superhydrophobic surface

We experimentally studied the effect of gas flow rate Q on the bubble formation on a superhydrophobic surface (SHS). We varied Q in the range of 0.001 < Q/Q_cr < 0.35, where Q_cr is the critical value for a transition from the quasi-static regime to the dynamic regime. The bubble geometrical parameters and forces acting on the bubble were calculated. We found that as Q increase, the bubble detached volume (V_d) increased. After proper normalization, the relationship between V_d and Q generally agreed with those observed for bubbles detaching from hydrophilic and hydrophobic surfaces. Furthermore, we found that Q had a minor impact on bubble shape and the duration of bubble necking due to the negligible momentum of injected gas compared to surface tension and hydrostatic pressure. Lastly, we explained the primary reason for the larger V_d at higher flow rates, which was increased bubble volume during the necking process. Our results enhanced the fundamental understanding of bubble formation on complex surfaces and could provide potential solutions for controlling bubble generation and extending the application of SHS for drag reduction, anti-fouling, and heat and mass transfer enhancement.