Rising of asymmetric bubble through milli-tubes: Experimental, theoretical and numerical analysis

Abstract

Appearance of Taylor bubble is ubiquitous in two-phase fluid flow through millimeter-sized tubes. Precise control over bubble generation and stability in those tubes are instrumental in unit processes in fine chemical industries. In this article, we systematically study the role of wall surface wettability in the structure and dynamics of the gaseous bubble flowing through water across milli-tubes. Specifically, from imaging experiments, we find that in a non-wettable milli-tube, the bubble loses its axial symmetry to reduce contact of the liquid phase with the tube wall. Moreover, we observe that the bubble speed is significantly higher in hydrophobic-coated tubes in comparison to the tubes without coating. Computational simulation balancing the viscous, gravitational, and surface forces recovers the observed effect of surface wettability on bubble shape and velocity. Finally, we establish the observed quantitative correlation between the bubble velocity and the surface wettability using an analytical model. Altogether, integrating experiments, numerical simulation, and theoretical analysis, we demonstrated the significant influence of wall-surface wettability in the shape and velocity of the Taylor bubble through milli-tubes.