Transport of beads, bubbles and droplets in cylindrical microchannel : The role of inertia and deformations - Jean Cappello (Institut Lumière Matière, Lyon)

When transported in microchannels at intermediate Reynolds number, beads, droplets or bubbles show interesting dynamics such as lateral migration. For rigid beads this migration is solely induced by inertial forces which lead to lateral motion of the particle until it reaches an equilibrium uncentered position in the microchannel. Transport of deformable objects as droplets or bubbles is even richer as the coupling between deformation and the external flow results in another lateral migration force whose orientation depends on the viscosity ratio of the two phases. I will present a study in which we investigate, both experimentally and numerically, the velocity and lateral position of beads, droplets and bubbles transported in a cylindrical pipe. By varying the object size, the viscosity ratio, the density, the Reynolds number and the capillary number, we offer an exhaustive parametric study exploring various dynamics from the non-deformable viscous regime to the deformable inertial regime, thus enabling us to highlight the sole and combined roles of inertia and capillary effects on lateral migration. Then, focusing on the specific case of bubbles, we further identify an intriguing regime at large deformations in which bubbles travel faster than the maximum velocity of the carrier flow. We rationalize this behavior in the limit of large bubbles and show that it originates from a reduction of the hydraulic resistance of the multiphase system. Finally, we determine the key parameters governing the onset of this “superfast” regime and demonstrate that it occurs only within a limited range of capillary and Reynolds numbers.

Contact: Elise Lorenceau