Bubble Formation in Yield Stress Fluids Using Flow-Focusing and T-Junction Devices

Area of Science:

• Fluid Dynamics
• Rheology
• Microfluidics

Background:

• Yield stress fluids (YSFs) exhibit complex flow behavior distinct from Newtonian fluids.
• Controlling bubble formation in YSFs is crucial for applications in materials science and chemical engineering.
• Existing methods for bubble production often struggle with the unique rheological properties of YSFs.

Purpose of the Study:

• To investigate the mechanisms of bubble production in yield stress fluids within axisymmetric T-junction and flow-focusing geometries.
• To leverage the yield stress property of fluids to achieve robust bubble breakup.
• To identify conditions for steady-state production of bubbly YSFs at larger scales.

Main Methods:

• Experimental study of bubble formation in YSFs using T-junction and flow-focusing devices.
• Analysis of fluid dynamics and breakup mechanisms, considering yield stress versus capillary stress.
• Investigation of gas pressure-driven flow dynamics and wall deposition effects.

Main Results:

• A robust bubble breakup mechanism was observed, analogous to Newtonian fluid behavior in 2D flow-focusing devices.
• Pressure-driven gas flow leads to unsteady dynamics due to hydrodynamic feedback and fluid deposition.
• Pathways for achieving steady-state bubbly YSF production were identified.

Conclusions:

• Yield stress plays a dominant role in bubble breakup in these geometries, enabling predictable formation.
• Unsteadiness in bubble production is linked to hydrodynamic instabilities and wall effects.
• The study provides a foundation for scalable, controlled production of bubbly yield stress fluids.