Abstract
We present simulations of clean drops rising into a layer of dissolved surfactant. Immediately after entering the surfactant layer, the drop is seen to accelerate suddenly as surfactant adsorbs onto its surface. The drop subsequently slows down to reach a terminal velocity that is between that of a clean drop and that of a solid object. For drops of viscosity equal to that of the ambient fluid, the terminal drop velocity, transition length, and maximal speed are all quantified and plotted against the Biot number, the ratio of convective to desorption timescales, and the adsorption number, the ratio of desorption to adsorption timescales. We find that faster sorption generally results in greater acceleration on entering the surfactant layer, a faster transition to equilibrium, and a faster terminal velocity. Drops of two different Reynolds numbers are considered to investigate the influence of inertial effects.
2 More- Received 13 June 2018
DOI:https://doi.org/10.1103/PhysRevFluids.4.014302
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