CO₂-induced baroclinicity in an interfacially-driven flow

Interfacial gas transport defines the behavior of many physical systems. The knife-edge viscometer (KEV) is a flow device for the study of interfacial phenomena consisting of a thin circular knife edge contacting the air-liquid interface of a liquid-filled cylinder. Knife-edge rotation conveys shear and mixing to the bulk via surface shear viscosity and fluid inertia. This work examined hydrodynamic changes in a KEV caused by CO₂ gas transport from the air-liquid interface, including the impact of density changes due to dissolved CO₂. Experiments consisted of planar laser-induced fluorescence flow visualization, a constant surface shear viscosity associated with a viscous monolayer, and variable rotation rate. Numerical simulations used an axisymmetric second-order finite difference code with a Boussinesq-Scriven surface model and variable bulk density. Results showed baroclinic production of vorticity by gradients of CO₂ that generated vigorous mixing and transport events, transients that decayed slowly in time due to CO₂’s large Schmidt number in water.