Adjustable behaviors and dynamic mechanisms of droplets in the cross junction

Dynamic behaviors of droplets transporting through the cross junction are experimentally and theoretically studied. The influences of initial droplet length, total flux, and flow rate combination of different inlets are systematically analyzed. Under the influence of the opposite flow, more types of flow patterns and different thresholds of two behaviors (breakup and obstruction) are obtained after a comparison with other references. Deformation characteristics in different patterns and stages are discussed in detail regarding the time-dependent lengths and their evolution rates. An empirical relation is proposed to estimate the time difference representing the unsynchronized necking, and the estimations agree well with the experimental results in all cases. Theoretical analysis of the rapid pinch-off during the breakup process proves the important role of the curvature component in the top view, which leads to the delayed onset of the pinch-off in the cross junction. Furthermore, the influence of the opposite flow is shown in flow pattern maps built in terms of the flow rate ratio and the normalized droplet length. To explain the adjustable functions of the cross junction at different flow rate ratios, two different mechanisms are proposed.