Abstract
This paper presents the results of numerical simulations of the unsteady motion of a single bubble that is released or injected into water. The governing equations are solved with a finite difference method using an adaptive boundary-fitted coordinate system. Results are shown for bubbles in the size range 0.72 to 1.5 mm. The effects of surfactants on the motion and shape of the bubble are investigated. When the surfactant concentration is sufficiently small, the bubble attains a maximum velocity before slowing down to its steady-state velocity. Although the steady-state velocity is nearly independent of surfactant concentration, the maximum velocity can be comparable to steady-state velocity in pure water. This behavior is observed even when the bubble is allowed to equilibrate prior to releasing it. The formation of an immobilized surfactant cap is observed soon after the bubble is released. The effect of the injection velocity on the bubble velocity profile is investigated. The effects of the sorption rate constants and the bulk surfactant concentration on the behavior of the bubble are investigated. The feasibility of using experimental measurements and simulations of unsteady bubble velocities to estimate sorption rate constants is discussed.
Published Version
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