Droplet coalescence at microchannel intersection chambers with different shapes.

Area of Science:

• Fluid Dynamics
• Microfluidics
• Interfacial Phenomena

Background:

• Droplet coalescence in microchannels is crucial for various applications.
• Understanding the influence of geometry on coalescence is essential for process control.

Purpose of the Study:

• To investigate how microchannel intersection chamber shape affects head-on droplet coalescence.
• To analyze the impact of chamber geometry on coalescence dynamics and critical conditions.

Main Methods:

• Utilizing high-speed camera visualization to observe droplet coalescence processes.
• Employing micro-particle image velocimetry (micro-PIV) to resolve internal flow patterns.
• Designing and testing three distinct chamber shapes: half-round, triangle, and camber.

Main Results:

• Camber junctions facilitate both direct and late coalescence, while half-round and triangle junctions exhibit only late coalescence.
• The critical capillary number (Ca*) varies with working systems and intersection shapes, being higher in camber junctions.
• Ca* decreases with increasing viscosity ratio for all tested intersection shapes.

Conclusions:

• Microchannel intersection chamber geometry is a key factor in controlling droplet coalescence modes.
• The camber shape offers greater flexibility in managing droplet interactions compared to half-round and triangle shapes.
• Flow field analysis provides insights into the mechanisms governing different coalescence behaviors.