Experimental study on the lateral migration of a bubble contaminated by surfactant in a linear shear flow

Abstract

Adding a small amount of surfactant to a gas–liquid two-phase flow can markedly change the dynamic behavior of its bubbles. In this study, the lateral motion of a single bubble (deq = 1.99–3.33 mm, Reb = 200–420) contaminated by surfactant and rising in a linear shear flow is experimentally studied. Sodium dodecyl sulfate (SDS) is chosen as the surfactant with concentrations ranging from 10 to 50 ppm. A curved screen is used to generate a stable linear shear flow, and particle image velocimetry is used to measure the quality of the flow field. Bubble motion parameters, including trajectory, aspect ratio, instantaneous velocity, and terminal velocity, are captured using the shadow method with charge-coupled device cameras. The lift coefficient C L is obtained by a quasi-steady-state analysis. The results show that the presence of surfactant inhibits the lateral migration of bubbles rising in a shear flow and that increasing the SDS concentration and bubble equivalent diameter strengthens this inhibition effect. That is, the C L and the net lateral migration distance decreased with SDS concentration and bubble equivalent diameter. In addition, the variation trends of the quasi-steady drag coefficient, bubble terminal velocity, and bubble oscillation frequency with bubble equivalent diameter and SDS concentration also were analyzed.