The influence of Marangoni convection on fluid dynamics of oscillating single rising droplets

• 3D simulations illuminating the impact of solutal Marangoni effects on oscillating droplets.
• Validation of numerical results with experiments in the toluene/acetone/water system.
• The initial droplet shape influences the rise behaviour of oscillating droplets.
• Irregular flow patterns induced by Maragoni convection trigger rise path oscillations.
• Excellent prediction of characteristic velocity for different soluteconcentrations.

The impact of solutal Marangoni convection on fluid dynamics and mass transfer cannot be described by means of analytical methods, due to their inherently three-dimensional, highly unsteady and non-linear nature. Hence, experimental and – to an increasing degree – numerical efforts are needed to reveal the underlying phenomena. This paper presents three-dimensional numerical simulations of an oscillating single droplet rising in a quiescent ambient liquid, with and without the Marangoni effect induced by the interfacial mass transfer of a solute. For the simulations, a CFD code based on the level set method was implemented in the open-source software OpenFOAM®OpenFOAM®. Experiments in the oscillating droplet regime have been carried out with the toluene/acetone/water system for different initial solute concentrations (reflecting different strengths of Marangoni convection) to obtain data for the validation of the numerical results. Comparisons between experimental and simulation results regarding the velocity, shape and trajectories of a rising droplet show a good qualitative and quantitative agreement. This will provide a basis for comprehensive mass transfer studies at deformable and oscillating droplets with simultaneous interfacial phenomena, such as Marangoni convection and surfactant adsorption, in the future.

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