Development and Validation of a Computational Methodology to Model Mass Transfer in Gas-Liquid Taylor Flow in a Circular Microchannel

Chemical microprocessing devices have great potential to perform mass transfer operations due to their ability to achieve high surface area density. Therefore, there is a great drive to employ microdevices for mass transfer in gas-liquid systems. The Taylor flow regime is the preferred regime in microchannels as it offers stable, periodic flow and there is internal mixing in each liquid slug. In this work, we have developed a computational methodology to model hydrodynamics and mass transfer in gas-liquid Taylor flow in a circular microchannel. The computational fluid dynamics (CFD) simulations are performed in a unit cell with a gas bubble and a liquid slug using OpenFOAM, an open-source CFD code. The flow of two phases is modeled using the volume of fluid (VOF) method, and mass transfer at the interface is modeled using the continuous compressive species transfer (CCST) method. The validation of the mass transfer model is performed with two benchmark problems, diffusion across the interface between two stagnant fluids and gas absorption via forced convection into a falling liquid film. For the modeling of Taylor flow, first a steady, periodic hydrodynamics is achieved and validated by comparison with the literature data. Subsequently, transient mass transfer simulations are performed for different values of dimensionless Schmidt numbers (0.1 < Sc < 10) by varying the liquid diffusivity. An extensive grid independence study is performed to ensure that the concentration boundary layer near the interface is captured accurately. The overall Sherwood number is calculated and is found to increase with an increase in the Schmidt number, whereas the Sherwood number decreases with an increase in the value of Henry's constant.