Structuring bubbles and foams in gelatine solutions within a circular microchannel device

Area of Science:

• Fluid dynamics
• Materials science
• Chemical engineering

Background:

• Microfluidic devices are crucial for precise control over fluid interfaces.
• Understanding bubble and foam formation is essential in various industrial applications.
• Gelatine solutions offer tunable properties for studying multiphase flows.

Purpose of the Study:

• To develop and characterize a circular flow-focusing device for generating monodispersed air bubbles and foams.
• To investigate different flow regimes (dripping, bi-disperse bubbly, bubbly, foam) by varying gas pressure.
• To analyze bubble formation mechanisms, volume dependence, and flow characteristics within the device.

Main Methods:

• Utilized a flow-focusing device with a circular cross-section.
• Varied gas pressure to study four distinct flow regimes.
• Analyzed bubble formation at the device exit and compared it to rectangular microchannels.
• Measured bubble volume, formation frequency, gas flow, and viscous resistance.

Main Results:

• Bubble volume was dependent on gelatine solution viscosity but not surface tension.
• Bubble formation frequency in bubbly flow was comparable to rectangular microchannels.
• Foam flow frequency was independent of gas pressure.
• Gas flow in bubbly and foam regimes followed a power law with applied pressure.
• Pressure drop laws were determined for each flow regime.

Conclusions:

• The circular flow-focusing device effectively produces monodispersed bubbles and foams.
• Viscosity is a key parameter controlling bubble size in this system.
• The device exhibits predictable flow behavior across different regimes, with power-law relationships observed for gas flow and pressure.
• This research provides valuable insights into microfluidic multiphase flow control for gelatine-based systems.