A numerical parameter study on the impact of Marangoni convection on the mass transfer at buoyancy-driven single droplets

Based on earlier successful validations of 3D simulations with experiments in a Marangoni dominated liquid/liquid system, this paper presents a numerical parameter study which investigates the effect of droplet diameter, kinematic viscosity ratio, interfacial tension gradient, and partition coefficient on the mass transfer of a solute via the Marangoni induced flow patterns. Simulation results exhibit a strong influence of droplet size on the mass transfer performance and reasonable agreement with experiments in the spherical droplet shape regime. In contrast to predictions based on the linear stability theory, the Marangoni convection was found to be unimpressed by a change in the kinematic viscosity ratio. For all kinematic viscosity ratios studied here, the mass transfer was significantly faster than in the system with constant interfacial tension (i.e. no Marangoni convection). The same is true for the interfacial tension gradient, which is the main driving force for Marangoni flow. Even if the gradient is decreased by a factor of 100, mass transfer enhancement factors >2 were found. Only an increase in the partition coefficient to a value of 10, and therewith a respective decrease in the concentration gradient at the interface, ended the dominion of the Marangoni effect on the mass transfer rate. (C) 2013 Elsevier Ltd. All rights reserved.