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Dynamics and dissolution of bubbles in microchannels : role of transverse migration forces and Marangoni stresses
This work focuses on the dynamics of a train of unconfined bubbles flowing in microchannels. We investigate the transverse position of a train of bubbles, its velocity and the associated pressure drop when flowing in a microchannel depending on the internal forces due to viscosity, inertia and capillarity. Despite the small scales of the system, the inertial migration force plays a crucial role in determining the transverse equilibrium position of the bubbles. Beside inertia and viscosity, other effects may also affect the transverse migration of bubbles such as the Marangoni surface stresses in presence of soluble surfactants, as well as the surface deformability for sufficiently large capillary number. The resulting migration force may balance external body forces if present such as buoyancy, centrifugal or magnetic ones. This balance not only determines the transverse position of the bubbles but, consequently, the surrounding flow structure, which can be determinant for any mass transfer process involved, as it will be demonstrated for bubble dissolution. Extension to droplet dynamics will finally be discussed, together with the presentation of a new micro-droplet generator.