Time-dependent mass-transfer behaviour under laminar and turbulent flow conditions in rotating electrodes: A CFD study with analytical and experimental validation

Abstract

Results of numerical calculations and their comparison with analytical expressions or experimental data under laminar and turbulent flow conditions are reported. It is predicted the transient and steady-state behaviour of mass-transfer coefficients and shear stresses in electrochemical reactors composed of rotating electrodes. Computational fluid dynamics (CFD) simulations were performed for both the rotating disc electrode (RDE) and the rotating cylinder electrode (RCE) considering the laminar or Reynolds-Averaged Navier-Stokes (RANS) equations. In this last case, it was assumed the Shear Stress Transport (SST) k-ω turbulence model sensitised by a correction term that accounts for streamline curvature and rotation. The hydrodynamics, coupled to the averaged diffusion-convection equation under transient conditions, was solved using the open source software OpenFOAM. A good agreement was attained between simulations and experimental or analytical results. In both rotating systems, a steady-state can be reached with an oscillatory behaviour that can be periodic in the case of laminar flow; depending on the Schmidt number, the interelectrode gap and the hydrodynamics. Also, the uniformity of the mass-transfer coefficient is lost under some circumstances. Finally, the full numerical code and a tutorial on how to use it, in order to perform simulations for the RDE or RCE, are supplied.