Mass transfer from a soluble wall into gas-liquid slug flow in a capillary tube

The mechanism of wall-liquid mass transfer of a solute in micro-scale systems has a huge relevance in many practical scenarios with particular interest for medical devices. A possible enhancement on this kind of phenomenon through the application of slug flow regime was studied with CFD techniques. Different flow conditions were considered to enable the inspection on the distinct hydrodynamics that may occur on the Taylor bubble surroundings in micro-scale. The VOF methodology was used to track the gas-liquid interface and the mass and hydrodynamic fields were simultaneously solved. The effects of the bubble passage on the mass transfer from a finite soluble wall to the flowing fluid were analyzed for each flow condition, and the corresponding mass transfer coefficients were quantified. Overall, this numerical work indicates that the flow due to the presence of one Taylor bubble leads to a moderate increase of the wall-liquid mass transfer coefficients. This increase can be enhanced if, instead of one, a continuous flow of bubbles is considered. The abrupt variation on the wall shear stress induced by the bubble movement is important to promote the referred increase. (C) 2018 Elsevier Ltd. All rights reserved.