Liquid Migration in Shear Thickening Suspensions Flowing through Constrictions

Area of Science:

• Rheology
• Fluid Dynamics
• Materials Science

Background:

• Dense suspensions often exhibit liquid migration (LM), becoming more dilute downstream through constrictions.
• Understanding the steady-state behavior of suspensions during extrusion is crucial for industrial processes.

Purpose of the Study:

• To investigate the steady-state concentration of shear-thickening suspensions during extrusion through a narrow die.
• To determine the relationship between output concentration, flow rate, and die geometry.
• To predict the output concentration using established rheological models.

Main Methods:

• Experimental extrusion of shear-thickening suspensions through a narrow die.
• Measurement of extrudate concentration over time and varying flow rates.
• Theoretical modeling coupling the Wyart-Cates model and the suspension balance model.

Main Results:

• The extrudate concentration (ϕ_{out}^{LM}) reached a steady state, independent of time and initial suspension concentration.
• At low flow rates, ϕ_{out}^{LM} was a universal function of the characteristic shear rate (Q/r_{d}^{3}).
• This steady-state concentration matched the critical input concentration (ϕ_{in}^{crit}) for LM onset.

Conclusions:

• Liquid migration in shear-thickening suspensions leads to a time-independent, universal output concentration.
• The observed behavior can be accurately predicted by combining models for shear thickening and solvent permeation.
• This finding provides a fundamental understanding of suspension behavior under flow confinement.