Bubble formation and departure from an underwater solid surface induce the surrounding liquid flow, impacting transport processes such as mass, momentum, or heat transfer in multiphase flow. The wettability of the surface is an important factor for this two-phase flow. In the present work, the two-phase flow with surfaces ranging from (super)hydrophilic to (super)hydrophobic is experimentally studied by using two-phase particle image velocimetry (PIV) to obtain the time-resolved velocity of the liquid phase and record the dynamic bubble profile simultaneously. The bubble profile is used to calculate local and transient capillary stress. A finite-difference method is applied to the high-repetition PIV data to obtain transient pressure, viscous stresses, and wall velocity gradients. Generally, increasing the surface hydrophilicity results in smaller bubbles, higher departure frequency, larger magnitudes of velocity and vorticity of the liquid phase, and stronger interaction between the liquid flow and the surface. The necking of the bubble prior to departure is found to follow the universal scaling law, for which the scaling coefficient varies with the surface wettability. As the bubble approaches pinch-off, the local capillary and liquid normal stresses at the neck become increasingly significant. The forces exerted on the bubble by the stresses show a relation to the bubble evolution prior to departure. Coalescence between predeparture and postdeparture bubbles tends to occur for hydrophilic surfaces, and the coalescence enhances the liquid flow. This study provides insights into how the surface wettability influences the coupling effect between the bubble dynamics and the surrounding liquid flow.

Close

PrevNext

View figure in article

• Bubble dynamics
• Multiphase flows