Hydrodynamics and mass transfer of Taylor bubbles flowing in non-Newtonian fluids in a microchannel

The paper presents a study on the mass transfer of Taylor bubbles flowing in non-Newtonian fluids (slug flow) using an oxygen-sensitive colorimetric method, for the bubble formation and flow stages. The effects of fluid rheology on the operation range, bubble length and bubble shape are first presented, showing that they can be well described by the effective viscosity. The concentration distribution and k L a are also altered by the fluid rheology. Such effect highly depends on the flow rates, leading to distinct phenomena under small and high flow rates. Nevertheless, for all the fluid systems the mass transfer can be described by three parts, the transfer through the caps, through the lateral film and the film-slug exchange. A mass transfer model is proposed accordingly, which shows a larger contribution of the film (20%-60%) in shear-thinning fluids than that in the Newtonian fluid (10%-25%).