For multiphase contactors, like bubble column reactors, it is of highest interest to predict how the gas dissolves and reacts in the liquid phase. This mass transfer process strongly depends on convection-dominated, extremely thin species boundary layers forming at the liquid-side of the bubble’s surface. Numerical simulations can play a significant role in understanding and predicting the complex interactions between flow dynamics and species transport, but the direct solution of both phenomena at the same time is currently not possible. This chapter summarizes two approximation approaches for the efficient and accurate simulation of convection-dominated concentration boundary layers. The first approach is a subgrid-scale model which allows to handle boundary layer widths that can be far smaller than the first cell layer at the interface in the computational mesh. Convective fluxes, diffusive fluxes and reaction source terms in the finite volume method are corrected based on non-linear reconstructions of the species boundary layer profiles normal to the interface. The second method is a hybrid simulation approach that solves the two-phase flow problem based on the Volume-of-Fluid method and uses a single-phase solver for species transport simulations. The concentration boundary layer is computed using a highly resolved surface-aligned single phase mesh.
