Experimental analysis of the unit cell approach for two-phase flow dynamics in curved flow channels

Flow behavior of gas–liquid mixtures in thin channels has become increasingly important as a result of miniaturization of fluid and thermal systems. The present empirical study investigates the use of the unit cell or periodic boundary approach commonly used in two-phase flows. This work examines the flow patterns formed in small tube diameter (<3 mm) and curved geometry flow systems for air–water mixtures at standard conditions. Liquid and gas superficial velocities were varied from 0.1 to 7.0 (～±0.01) m/s and 0.03 to 14 (～±0.2) m/s for air and water respectively to determine the flow pattern formed in three geometries and dispersed bubble, plug, slug and annular flow patterns are reported using high-frame rate videography. Flow patterns formed were plotted on the generalized two-phase flow pattern map to interpret the effect of channel size and curvature on the flow regime boundaries. Relative to a straight a channel, it is shown that a ‘C shaped’ channel that causes a directional change in the flow induces chaotic advection and increases phase interaction to enhance gas bubble or liquid slug break-up thus altering the boundaries between the dispersed bubble and plug/slug flow regimes as well as between the annular and plug/slug flow regimes.