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Constriction length dependent instabilities in the microfluidic entry flow of polymer solutions
Mahmud Kamal Raihan1, Sen Wu1,2, Yongxin Song2
1Department of Mechanical Engineering, Clemson University, Clemson, SC 29634-0921, USA. xcxuan@clemson.edu.
Soft Matter
|September 30, 2021
Summary
Flow instabilities in microfluidic contractions and expansions depend on fluid type and constriction length. Viscoelastic polyethylene oxide (PEO) solutions show strong length-dependent instabilities, unlike xanthan gum (XG) or water.
Area of Science:
- Fluid dynamics
- Rheology
- Microfluidics
Background:
- Transport phenomena in contraction-expansion geometries are crucial for many applications.
- Polymer solutions introduce complex flow behaviors in microfluidic systems.
- The impact of constriction length on flow instabilities in microfluidic entry flow remains poorly understood.
Purpose of the Study:
- To investigate the influence of constriction length on rheological responses and flow instabilities.
- To analyze the interplay between shear and extension dominated flow regimes in microfluidic entry flow.
- To differentiate the behavior of various polymer solutions and Newtonian fluids under varying constriction lengths.
Main Methods:
- Experimental investigation of planar contraction-expansion microchannels with varying constriction lengths.
- Utilizing three distinct polymer solutions: viscoelastic polyethylene oxide (PEO), shear-thinning xanthan gum (XG), and shear-thinning/viscoelastic polyacrylamide (PAA), alongside Newtonian water.
- Observing and analyzing rheological responses and flow instabilities.
Main Results:
- Viscoelastic polyethylene oxide (PEO) solutions exhibit significant constriction length-dependent instabilities in both contraction and expansion flows.
- Shear-thinning xanthan gum (XG) solutions and Newtonian water show no dependence on constriction length.
- Shear-thinning and viscoelastic polyacrylamide (PAA) solutions display constriction length dependence exclusively in the expansion flow.
Conclusions:
- Constriction length significantly impacts flow instabilities in viscoelastic fluids, particularly PEO solutions.
- The absence of this dependence in Newtonian fluids and XG highlights the role of viscoelasticity.
- PAA solutions demonstrate a unique behavior, with instabilities appearing only in expansion flow, suggesting complex viscoelastic and shear-thinning interactions.
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