Article
Wettability Effects on Breakup Dynamics of Surface Nuclei in Shear Flows (en)
* Presenting author
Abstract:
While heterogeneous nucleation in the context of cavitation and boiling processes has been extensively researched, there is still limited knowledge regarding the influence of substrate wettability. Wettability affects the mobility of the three-phase contact line, thereby influencing the morphology and dynamics of the bubble in the growth and detachment phases. We investigated detachment processes of wall-attached nuclei in shear flow with varying wall shear rate on substrates with different contact angle hysteresis Δθ. The nucleation sites are cylindrical blind holes with a diameter 200 μm. The liquid is oversaturated with dissolved air, allowing wall-attached gas bubbles to grow convectively-diffusively until reaching a critical size and detaching. The kinematics of the detachment process are captured in shadowgraphy using a high-speed camera at 100,000 frames per second.The size of the detached bubbles and the underlying mechanism of disintegration depend on the particle-based Reynolds or Weber number, and Δθ. At low wall shear rates, detachment occurs through dynamic wetting processes and sliding along the substrate. As the shear rate increases, the bubble oscillates and disintegrates through a self-induced vibration, i.e., a fluid-dynamic instability. The studies emphasize the necessity of incorporating wettability into the physical modeling of bubble detachment as a detachment criterion.