Direct numerical simulation of mass transfer from Taylor bubble flow through a circular capillary

In this work mass transfer during a Taylor bubble flow regime has been investigated by a volume of fluid (VOF) based numerical method. The hydrodynamics of Taylor bubble flow through a circular capillary has been simulated in a single unit cell by a moving reference frame. The validity of Taylor bubble hydrodynamics simulation has been checked by comparing the liquid film thickness and the relative bubble velocity obtained from computational fluid dynamics (CFD) simulations with reported empirical correlations and experimental results. The conservation equation of tracer has been solved in whole of flow domain for simulating mass transfer from Taylor bubble to surrounding liquid. The tracer concentrations in the cells that are either completely or partially filled with the gas phase are assigned the equilibrium concentration by employing the concept of internal boundary condition. By this concept an artificial diffusion of tracer has been appeared in the simulations. In order to eliminate this artificial diffusion, the advection scheme in the tracer conservation equation has been modified by using the two film mass transfer model. The simulation of mass transfer from a single bubble has been validated by comparing the CFD results with reported experimental data. Afterwards, the effects of capillary number, unit cell length and capillary diameter variation on mass transfer from Taylor bubble has been investigated.