General correlations for gas-liquid mass transfer in laminar slug flow

Mass transfer is an important phenomenon that can be highly leveraged through hydrodynamics. Slug flow is frequently associated with the enhancement in transport phenomena, and so, mass transfer from a single Taylor bubble to the flowing liquid is numerically studied. This CFD work validates a recently published study using pure oxygen bubbles and expands it to pure bubbles of other compounds (different Schmidt numbers) for different Reynolds numbers. The simulations were performed with VOF + PLIC to track the gas-liquid interface. Flow and mass fields were solved simultaneously based on the "species transport" model and imposing a constant concentration at the interface. The results confirmed that the solute around the bubble remains in a thin layer along the nose and film regions. At the bubble rear, it accumulates in the wake due to the closed liquid recirculation characteristic of laminar flow. Local and global mass transfer coefficients were also determined for these characteristic hydrodynamic regions. The data showed a higher impact of the nose and film on the overall mass transfer, so a general correlation between Sherwood, Reynolds and Schmidt numbers was derived for each of these regions. The developed correlations offer a good prediction of the mass transfer (deviations around 10-20%).