Visualization of Core-Annular Microfluidic Flows
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2018
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Swarthmore College. Dept. of Engineering
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en
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Abstract
Nanotechnology, especially that involving hydraulic or fluid flows, is promising to revolutionize the field
of medicine and scientific research. Lab on a Chip devices and DNA microarrays are promising technology for in
vivo-like study and personalized medicine. However, in order to efficiently design these devices we need to
llllderstand fluid dynamics at intersections at a microscopic level. Previous studies have probed the microfluidic
characteristics of laminar flows, including the modeling of blood flow and the study of flow through converging
channels. However, not all flow is planar, and other groups have studied the dynamics of core-arumlar flow, a
particularly fascinating effect where one fluid is encapsulated within the other. We report the creation of robust
microfluidic devices for core-annular flow study, allowing dynamic imaging of flows up to Re = 400. Fwthermore,
we rigorously characterize the flow cmvature and interface profile for intersecting flows of the same viscosity over a
wide variety of flow conditions, using modules with rectangular channels of equal size, a common geometry that is
easy to fabricate using soft lithography techniques. The flow profiles were categorized into four flow regimes:
planar, curved, transitional, and annular flow, and the effect on flow cmvature of changes in Reynolds nwnber, flow
ratio (Q), channel width, and intersection angle was determined. Three modules were used: two with 90° channel
intersections, with channel sizes of 129 ).lm X 100 ).lm and 200 ).lm X 100 ).lm, and one with a 45° channel
intersection, with channels 161 ).lm wide by 100 ).lm tall. An increase in Reynolds nwnber was fOlllld to increase the
interface curvature, eventually leading to annular flow. Similarly, and increase in Q was fOlllld to slightly increase
the flow cmvature, while increasing channel width and decreasing intersection angle both drastically decreased flow
cmvature. For the more square 90° module, annular flow was obtained at Re = 158 and above, while for the
rectangular 90° module annular flow was not obtained lllltil Re = 274. Finally, for the module with a 45° intersection,
annular flow was obtained at Re = 391 and beyond. The findings presented suggest that inertia plays the leading role
in annular formation when the flows are of equal viscosity and missible, and the effect of various real-world
parameters are carefully parsed out. While viscosity and interfacial free energy effects may dominate the flow
patterns when they are present, this paper characterizes the inertial forces that may be otherwise missed or may
complicate the analysis of more complex situations.