Flow patterns and dynamic mechanisms of immiscible fluids in cross junctions with different aspect ratios

Abstract

The flow patterns of immiscible liquids in microscale cross junctions are experimentally studied and the influencing factors including the capillary number (3 × 10−4–6 × 10−1), flow rate ratio (0.004–60), viscosity ratio (0.04–2.8), and channel aspect ratio (1/3–1) are systematically analyzed. Evolutions of the interfacial morphologies in different flow patterns are discussed with the aid of force analysis. In the droplet group, two different breakup modes of the liquid thread are found with the symmetric mode for squeezing and the asymmetric mode for dripping, which are divided by a critical capillary number around 0.01. Two different physical models for constructing the scaling law of the droplet length are compared over large ranges of flow parameters and the universal scaling law is valid to identify the transitional boundary between squeezing and dripping regimes. In the jet group, the jet width in different channels is compared to the theoretical prediction. A detailed comparison between the experimental results in jetting and the linear instability theory is further conducted and the reason for the polydispersity of the droplet size in widening jetting is found. Finally, the flow pattern maps are built using dimensionless parameters in both the global terms and the local terms. In contrast, the local dimensionless parameters are confirmed to show a better performance in unifying the transitional boundary between two groups of flow patterns. The obtained results should be useful for the further understanding of the dynamic mechanisms of the microscale multiphase flow.