Lattice Boltzmann study of mass transfer for two-dimensional Bretherton/Taylor bubble train flow

This work presents a procedure for the determination of the volumetric mass transfer coefficient in the context of lattice Boltzmann simulations for the Bretherton/Taylor bubble train flow for capillary numbers 0.1. . 0.7) [1]. In the latter case the bubble shape is asymmetric and cannot be approximated through flat surfaces and circular circumferences as is often done in the literature [2,3]. When the vortex is present in the slug, the scalar concentration is well mixed and it is common to use periodic boundary conditions and the inlet/outlet-averaged concentration as the characteristic concentration. The latter is not valid for flows where the tracer is not well mixed, i.e. Ca>. 0.7. We therefore examine various boundary conditions (periodic, open, open with more than 1 unit cell) and definitions of the characteristic concentration to estimate mass transfer coefficients for the range of capillary numbers 0.1.