Purely elastic flow instabilities in microscale cross-slot devices

Area of Science:

• Fluid dynamics
• Rheology
• Microfluidics

Background:

• Investigating viscoelastic fluid behavior in microfluidic devices is crucial for understanding complex flow phenomena.
• Low Reynolds number flows in microgeometries are sensitive to fluid viscoelasticity and confinement effects.

Purpose of the Study:

• To experimentally study viscoelastic fluid flow in a cross-slot microgeometry.
• To determine the influence of polymer concentration and microchannel bounding walls on flow patterns and elastic instabilities.

Main Methods:

• Utilized several viscoelastic fluids in a cross-slot microfluidic device.
• Conducted experiments under low Reynolds number flow conditions.
• Varied polymer solution concentration and channel aspect ratio (depth to width).

Main Results:

• Concentrated polymer solutions showed flow bifurcation at a critical Weissenberg number (Wi), leading to steady asymmetric flow.
• Elastic instability onset and type depended on channel aspect ratio and polymer concentration.
• Higher aspect ratios (reduced wall effects) promoted two instabilities: steady asymmetric flow followed by time-dependent flow.
• Decreasing aspect ratio stabilized the flow, delaying transitions to asymmetric and unsteady states.
• Less concentrated solutions lacked the steady asymmetric instability, only exhibiting time-dependent flow instability.

Conclusions:

• Microchannel bounding walls exert a significant stabilizing effect on viscoelastic flow instabilities.
• Flow behavior transitions from steady asymmetric to time-dependent instabilities are tunable via channel geometry and fluid concentration.
• The Weissenberg number serves as a critical parameter for predicting elastic instabilities in confined viscoelastic flows.