Equilibrium Taylor bubble in a narrow vertical tube with constriction

Air Taylor bubbles in a millichannel filled with water are characterized by an elongated shape, a bullet-shaped nose (head), and a comparatively flat tail. Many experimental and numerical investigations have been performed in the past. Yet, most of them consider Taylor bubbles in a straight channel with constant cross section. The effect of a local change in the channel geometry on both the bubble shape and the flow fields on each side of the gas–liquid interface is, however, difficult to predict. In this work, we present experimental data obtained in a vertical millichannel, where the flow is moderately obstructed by a constriction, whose ratio ranges from 10% to 36%. We find that the Taylor bubble takes an equilibrium position for downward liquid flow with 264.36 Re 529.67 and 264.36 Re 728.29 for 10.17% and 18.06% constriction ratios, respectively. In this area, an empirical correlation characterizing the bubble head is provided. Other flow regimes, such as bubble breakup, co- and countercurrent configurations, are identified and shown in the form of a regime map. The results, besides their relevance in process engineering, exhibit high reproducibility and will serve as a reference for future interface-resolving two-phase flow simulations.