Liquid–liquid segmented flows in polycarbonate microchannels with cross-sectional expansions

Liquid–liquid segmented flows in microchannels fabricated on polycarbonate test chips were investigated experimentally. Three different cross-sectional expansion ratios of 16, 4, and 2 from the injection to the test channels were used to observe the effect of different cross-sectional areas of the injection channel on the segmented flow regimes in the test channel. Flow regime maps and the transitions between flow regimes were determined for the different expansion ratios. The effect of the cross-sectional expansion ratio was determined by mutual comparison of these results. The measured length of the dispersed fluid segments was found to scale inversely with the carrier fluid volumetric flow ratio (βC). A simplified geometric model for the volume of the dispersed and the carrier fluid plugs provided good estimates of the carrier plug length, which scaled inversely with (1 − βC). Velocity and pressure drop measurements of the liquid–liquid segmented flows were carried out for all flow regimes, and the associated trends were correlated with changes in the flow topology. Most previous homogeneous and separated flow models based on the viscous frictional pressure drop underestimated the measured pressure drops. Including the contribution of the capillary pressure drop in addition to the frictional pressure drop improved the agreement with the measured data.