Experimental validation of plugging during drop formation in a T-junction.

Area of Science:

• Fluid Dynamics
• Microfluidics
• Interfacial Science

Background:

• Drop formation in T-junctions at low capillary numbers is primarily governed by interfacial effects.
• The
• squeezing
• mechanism, where continuous fluid pressure pinches off dispersed fluid, is theoretically understood but experimentally unverified regarding pressure dynamics.

Purpose of the Study:

• To experimentally investigate and validate the pressure dynamics during T-junction drop formation.
• To identify the precise pressure changes responsible for drop pinch-off.
• To explore the influence of capillary number on pressure oscillations and the underlying formation mechanism.

Main Methods:

• Development and utilization of novel Laplace sensors for high-speed, localized pressure measurements within a T-junction.
• Empirical study of pressure variations in both continuous and dispersed fluid phases during the drop formation process.
• Analysis of pressure data across a range of capillary numbers to determine the dominant formation mechanisms.

Main Results:

• Experimental confirmation of the pressure rise predicted by the
• squeezing
• mechanism.
• Discovery of anti-phase pressure oscillations between the continuous and dispersed fluid phases.
• Observation that pressure oscillations persist even at high capillary numbers, indicating a combined formation mechanism.

Conclusions:

• The study validates the
• squeezing
• mechanism and provides the first experimental evidence of the associated pressure dynamics.
• Drop formation in confined geometries involves a combination of squeezing and shearing forces, not solely shear-driven, even under conditions favoring monodisperse drop production.
• The findings offer crucial insights into microfluidic drop generation and control.