Systematic analysis of high Schmidt number turbulent mass transfer across clean, contaminated and solid interfaces

A series of numerical simulation is carried out for high Schmidt number turbulent mass transfer across interfaces of different dynamical conditions, i.e., a clean or contaminated free surface and also a solid surface. A distinct feature of free surface turbulence close to a contaminated interface is drastic damping of the surface divergence fluctuations at low frequencies, which play a critical role in the interfacial mass transfer. Various concentration statistics reveal that the transport mechanism at a highly contaminated interface becomes dynamically equivalent to that at a solid surface. Consequently, the interfacial mass transfer rate falls down to the value on a solid surface, so that the Schmidt number dependency of the mass transfer rate switches from Sc−0.5 to Sc−0.7. Based on a one-dimensional advection–diffusion equation, it is demonstrated that the ratio between typical intensity and frequency of the fluctuating surface divergence is a critical parameter for the transition of the turbulent mass transfer mode.