Experimental study of air-water two-phase flow pattern evolution in a mini tube: Influence of tube orientation with respect to gravity

•Visualization of several two-phase flow patterns in a capillary tube at small superficial velocities.•Analysis of the evolution of the flow patterns from inlet location (L/D=10) to far downstream location (L/D=420).•Highlight phenomena like coalescence or breakup of dispersed phase along the tube.•Investigation of the effect of gravity (tube orientation) on flow patterns and two-phase flow maps.