Interfacial turbulence enhances oxygen transport into shallow liquid layers

Transport of oxygen from the gas phase into shallow layers of water and diluted sulfuric acid has been investigated. To this purpose, the temporal evolution of the oxygen concentration in the liquid layers was followed at fixed vertical positions by an oxygen-sensitive electrode. The vertical position of the electrode was varied in 0.1 mm steps. The oxygen concentration profiles were reconstructed from the measured data. As expected, the transport of oxygen into a water layer occurs by diffusion. In contrast, spontaneous interfacial turbulence was found to develop during the transport of oxygen into a shallow layer of sulfuric acid, causing a pronounced deviation from a diffusion profile in a 0.5 mm region underneath the gas/liquid interface. In this topmost layer, surface tension-driven (Marangoni) convection is the dominant transport mechanism, while the bulk liquid layer that extends from 0.5 mm below the interface to the bottom is hydrodynamically quiescent and transport by diffusion prevails.