Entrapment and cross-flow transport of air bubbles by a hydrophobic strip in a turbulent channel flow

• Published in: Experiments in fluids Vol. 62; no. 9
• Main Authors: Kitagawa, Atsuhide, Denissenko, Petr, Murai, Yuichi
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-09-2021; Springer Nature B.V
• Subjects: Aerodynamics; Air bubbles; Bubbles; Ceilings; Channel flow; Contact angle; Cross flow; Deformation; Drag coefficients; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Entrapment; Fluid dynamics; Fluid flow; Fluid- and Aerodynamics; Formability; Heat and Mass Transfer; Hydrophilicity; Hydrophobicity; Research Article; Reynolds number; Shear flow; Strip; Turbulent flow; Weber number
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-021-03288-3

We experimentally investigate air bubbles sticking to a hydrophobic strip on a hydrophilic ceiling in a horizontal turbulent channel flow. Simultaneous measurements of wall-sticking bubbles are conducted in two perpendicular planes using two cameras to estimate their size and contact angles and hence evaluate the drag coefficient. In a range of the bubble Reynolds number, Re
b
(250 ≤ Re
b
 ≤ 1480) and a range of the Weber number, We (0.7 ≤ We ≤ 6.5), the drag coefficient for a single, deformable bubble stuck on the surface is almost independent of Re
b
and We and tends to be slightly higher than that of a non-deformable bubble fixed on a wall in linear shear flow. We also investigate the entrapment and cross-flow transport of air bubbles using an oriented hydrophobic strip on a hydrophilic surface. Bubbles creeping along the hydrophobic strip become trapped when reaching its edge where the downstream contact angle changes. When the strip edge is inclined relative to the flow, bubbles creep along the hydrophobic–hydrophilic boundary and thus move in the cross-stream direction. The cross-stream transport of the bubbles strongly depends on the channel Reynolds number and the angle between the hydrophobic strip and the stream.
Graphic abstract