Hydrodynamic Analysis\nof Polymer–Salt Aqueous\nTwo-Phase Systems in a Millifluidic Channel

The integration of aqueous two-phase systems (ATPSs)\nwith microfluidics\ndelves into the possibility of a wide spectrum of applications. The\neffectiveness of these integrated processes depends on the hydrodynamic\nstudy of two immiscible aqueous streams. This work investigates the\nhydrodynamics of three different polymer–salt ATPSs in a millifluidic\nchannel. The flow patterns noted during the flow experiments are categorized\nas droplet, slug, jetting, irregular, and stratified flows. The interplay\nof forces between two liquids at the junction is the determining factor\nfor the type of flow pattern in the channel. Dimensional analysis\nwas carried out to propose a universal flow regime map based on unified\ndimensionless numbers (<i>We.Ca</i><sup>0.5</sup>) to satisfactorily\nsegregate the observed flow patterns of different polymer–salt\nATPSs studied. Further, the slug length (<i>L</i><sub>s</sub>) is an integral parameter that defines the effectiveness of transport\nand encapsulation processes. The predictive empirical correlations\nfor the calculation of the slug length (<i>L</i><sub>s</sub>) of the stable continuous-dispersed flow patterns based on competing\nstresses, flow rate ratio (<i>Q</i><sub>R</sub>), and viscosity\nratio (μ<sub>R</sub>) are proposed for polymer–salt ATPSs\nin general. The proposed correlations predict the slug length with\nan average standard deviation of ±5%. Further, two empirical\ncorrelations were proposed for <i>Q</i><sub>R</sub> <\n1 and <i>Q</i><sub>R</sub> ≥ 1, which predict the\nslug length with an average deviation of ±3.44 and ±3.87%,\nrespectively.