Hydrodynamically enhanced electrochemical mass transfer on the surface of an electrically conductive droplet

A fully coupled model is proposed to investigate the influence of flow on electrochemical mass transfer at the interface between the electrolyte and an electrically conductive droplet. The electric current flows through the droplet, and consequently the droplet acts as both anode and cathode. Computations of flow, concentration of reactant, and electric current density fields were carried out. Various droplet sizes (0.5, 2, 4 mm) under different flow regimes considering Reynolds number (Re = 0.2, 2, 20, 40 and 80) were investigated. An iterative numerical method is proposed to determine the concentration of reactant and electric current density at droplet-electrolyte interface considering the reaction kinetics (Butler-Volmer) formula and the diffusion-advection of the reactant through the hydrodynamic boundary layer around the droplet. With the increase of Reynolds number, the amount of electric current density which flows through the droplet increases. It is found that the mass transfer at droplet-electrolyte interface is controlled by reaction kinetics for the small droplet (0.5 mm). However, the diffusion of the reactant governs the efficiency of mass transfer with the increase of the droplet size (2 and 4 mm). With the increase of Reynolds number, the anodic area on the surface of droplet is enlarged.