AC electrified jets in a flow-focusing device: Jet length scaling

Area of Science:

• Fluid dynamics
• Microfluidics
• Electrical engineering

Background:

• Microfluidic devices with integrated electrodes control water-in-oil drop production.
• Previous work showed AC fields can form very long jets.

Purpose of the Study:

• Investigate long jet formation as a function of electrical parameters: water conductivity, signal frequency, and voltage amplitude.
• Characterize the transition from uniform jets to unstable liquid structures.

Main Methods:

• Utilized a microfluidic flow-focusing device with integrated electrodes.
• Varied electrical parameters (conductivity, frequency, voltage) to observe jet behavior.
• Employed a distributed element circuit model to analyze electrical response and jet tip potential.

Main Results:

• Identified a threshold voltage for rapid jet length increase at intermediate frequencies.
• Observed a smooth increase in jet length with voltage at high frequencies.
• Characterized the transition to unstable liquid structures with a voltage-conductivity diagram.
• Determined jet breakup occurs at a critical electric potential (~550 V).

Conclusions:

• Electrical parameters significantly control jet morphology and stability in microfluidic devices.
• Jet breakup is linked to a critical electric potential at the jet tip.
• The findings provide insights into controlling droplet generation in microfluidics.