Experimental study of bubble flow dynamics in an asymmetric hierarchical porous structure

Porous media have been widely used for liquid–gas separation, benefiting from the strong capillary force generated by micro/nanoscale pores. Understanding the flow characteristics at the pore scale is important for the design of porous structures. In this study, the flow mechanisms of an isolated bubble in an asymmetric hierarchical pore were investigated by high-speed flow visualization and microscopic particle image velocimetry (Micro-PIV). The influence of the hierarchical pore on the flow field in the liquid and the dynamics of bubble penetration was investigated using isopropyl alcohol as the test liquid and polydimethylsiloxane micromodels. The critical pressure for the bubble to break through the pore was determined. The results show that the presence of secondary microstructure can increase the critical bubble point pressure by 79.7%. Meanwhile, the attack angle of the microstructure affects the critical pressure differently by changing the pinning effect, the curvature of the bubble as well as the flow field. The results of this work could provide guidance for optimizing the design of porous media for efficient gas–liquid separation.