Rising and breakup of air in viscous fluids in confined space

The dynamics of liquid-gas interface in confined geometries is fundamentally interesting and relevant for various applications, e.g., related to microfluidics. Recently, we have explored various issues on this, from which we pick up latest three. One is rising dynamics of an air bubble surrounded by viscous liquid in a doubly confined geometry [1]. The system is confined by not only front and back plates of the cell (as in a Hele-Shaw cell) but also the side plates. We establish scaling laws for the rising velocity and drag friction, and further reveal a close relation to an unresolved classic problem regarding viscous fingering. Second is breakup of air induced by a solid disk freely falling in viscous liquid in a Hele-Shaw cell [2]. We discuss a new self-similar regime for the breakup in which the section of air before breakup is not axisymmetric but an ellipse [3]. Third is an unusual case of capillary dynamics, which is not slowing down (thus, different from usual capillary imbibition) but is accelerating. We demonstrate a unified description for the two opposite dynamics [4].
[1] Mayuko Murano & KO, Phys. Rev. Research 2020.
[2] Hana Nakazato & KO, under review.
[3] Hana Nakazato, Yuki Yamagishi & KO, Phys. Rev. Fluids 2018.
[4] Julie André & KO, Langmuir 2020.