Gas transport in an interfacially-driven biochemical reactor

Gas transfer at interfaces is a limiting factor in the performance of many chemical reactors and bioreactors. The knife-edge surface viscometer (KEV) is a flow apparatus in which a thin, rotating ring at the surface of a liquid conveys shear and mixing to the bulk fluid primarily through the surface shear viscosity and secondary inertial flow.  Here we examine the effects of interfacial shear and surface shear viscosity on gas transfer using a KEV.  Simulations using COMSOL were compared to CO₂ transport measurments with varying Reynolds (Re) and Boussinesq (Bo) numbers. Experiments used a pH sensitive fluorescent dye to visualize CO₂ transport over time in the KEV with different amounts of steric acid, an insoluble surfactant forming a monolayer. Good agreement is found between the experiments and the simulations. Results show a monotonic increase in gas transfer with increasing Re and increasing Bo.  These results are relevant to applications and future studies in chemical reactors, bioreactors, and gas transfer in microgravity studied using the ring-sheared drop (RSD), a containerless bioreactor launched to the ISS in 2019, originally designed to study amyloid fibrillization without interaction with solid walls. As a bioreactor, the RSD allows for optimal gas exchange due to increased interfacial area.