Abstract
Here we map gas–liquid two-phase flow regimes observed in polymeric microchannels with different wetting properties. We utilized video and confocal microscopy to examine two-phase flow patterns produced by parallel injection of air and water through a Y-shaped junction into a rectangular microchannel made of poly(dimethylsiloxane) (PDMS). We observed seven flow regimes in microchannels with hydrophobic walls, whereas only two flow patterns were identified in hydrophilic microchannels. Our study demonstrates that surface wettability has a profound influence on the spatial distribution of air and water moving in microchannels.
Highlights
Two-phase flows are encountered in a wide range of applications including heat exchangers, oil/gas processing and transport, nuclear and chemical reactors, cryogenics, air pollution control, food production and rocketry
It was noted that there existed maximum flow rates of air and water beyond which the conformal seal between PDMS surfaces failed due to extremely high pressure generated by fluid pumps, and the microchannel became no longer operational
Weber number (We) show that surface hydrophobicity in rectangular elastomeric microchannels results in six types of stratification of air–water two-phase flow with various interfacial shapes, and breakup of the water stream into droplets originating from two-phase instabilities
Summary
Two-phase flows are encountered in a wide range of applications including heat exchangers, oil/gas processing and transport, nuclear and chemical reactors, cryogenics, air pollution control, food production and rocketry. Despite the increased effect of surface forces, the focus of previous studies on microscale multiphase flows was primarily on the effect of fluid properties [28], channel geometry [29,30], orientation [31,32] and size [31,33,34] on the morphology of gas–liquid two-phase flows in small capillary tubes or microchannels fabricated in glass or silicon. We varied the hydrophobicity of the PDMS microchannels using a plasma-mediated surface modification method and injected air and water in parallel without premixing to generate high-speed air– water two-phase flows in a horizontal rectangular microchannel that is 300 μm in width, 100 μm in height and 1 cm in length In this system, confinement number (Co) and Eotvos number (Eo) were estimated to be 18.2 and 13 109.3, respectively. We show a dramatic difference in two-phase flow patterns caused by channel hydrophobicity; we found seven flow regimes in hydrophobic microchannels and two in hydrophilic channels
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