Transverse migration of single bubbles in simple shear flows

Abstract

Trajectories of single air bubbles in simple shear flows of glycerol–water solution were measured to evaluate transverse lift force acting on single bubbles. Experiments were conducted under the conditions of −5.5⩽ log 10 M⩽−2.8 , 1.39⩽ Eo⩽5.74 and 0⩽| dV L/ dy|⩽8.3 s −1 , where M is the Morton number, Eo the Eötvös number and d V L /d y the velocity gradient of the shear flow. A net transverse lift coefficient C T was evaluated by making use of all the measured trajectories and an equation of bubble motion. It was confirmed that C T for small bubbles is a function of the bubble Reynolds number Re, whereas C T for larger bubbles is well correlated with a modified Eötvös number Eo d which employs the maximum horizontal dimension of a deformed bubble as a characteristic length. An empirical correlation of C T was therefore summarized as a function of Re and Eo d . The critical bubble diameter causing the radial void profile transition from wall peaking to core peaking in an air–water bubbly flow evaluated by the proposed C T correlation coincided with available experimental data.