Effects of surface wettability on pool boiling nucleation from artificial cavities

Boiling heat transfer is an effective cooling strategy for high-heat-flux devices, and its performance is significantly influenced by the dynamics of bubble nucleation, growth, and departure. This study experimentally investigates controlled bubble behaviour on artificial cavities using deionised water and three boiling surfaces with different wettabilities: hydrophilic silicon oxide (SiO₂), hydrophobic perfluorodecyltrichlorosilane (FDTS), and superhydrophobic Glaco. Distinct bubble interaction regimes were observed across these surfaces and fluids. Results are compared with FC-72 having contrasting thermophysical properties. On the hydrophilic SiO₂ surface, bubbles in deionised water exhibited growth behaviour similar to that previously reported for FC-72, characterised by elliptical bubble shapes and minimal contact areas anchoring the bubbles to the surface. On the hydrophobic FDTS surface, the water vapour bubble contact area increased during early growth but decreased rapidly before departure, leaving a residual vapour layer that facilitated continuous bubble generation from cavity-assisted nucleation sites. In contrast, the superhydrophobic Glaco surface formed a vapour layer extending beyond the actual bubble departure diameter that suppressed cavity-controlled nucleation and promoted the direct formation of larger bubbles, with a nearly constant bubble-surface contact area throughout growth. Under comparable heating conditions, bubble diameters on the FDTS and Glaco surfaces demonstrated similar linear growth trends in deionised water. However, bubble departure diameters increased with surface wettability due to enhanced surface tension forces at the solid-liquid interface. These results illustrate that surface wettability and fluid properties jointly dictate bubble dynamics, providing insights for the rational design of boiling surfaces to optimize heat transfer performance.