Mixing with herringbone-inspired microstructures: overcoming the diffusion limit in co-laminar microfluidic devices

Area of Science:

• Microfluidics
• Electrochemistry
• Chemical Engineering

Background:

• Efficient mixing is crucial in laminar microfluidic devices to overcome diffusion-limited transport.
• Membraneless redox flow cells face challenges in achieving convective mixing and reactant separation simultaneously.

Purpose of the Study:

• To develop and evaluate microfluidic flow promoters for enhanced mixing and separation in membraneless redox flow cells.
• To investigate the impact of flow regimes on mass transport and reactant stratification.

Main Methods:

• Design and implementation of herringbone flow promoters with integrated separation zones.
• Electrochemical experiments using a model redox couple.
• Micro laser-induced fluorescence (μLIF) for flow visualization.
• Micro particle image velocimetry (μPIV) for flow field analysis.

Main Results:

• Optimized herringbone structures promote convective mixing and thin boundary layers.
• Flow regimes transition from laminar to turbulent with increasing flow rates, altering Sherwood number scaling (Sh ~ Re^0.29 to Sh ~ Re^0.58).
• Stable co-laminar flow is maintained up to Re ~325, with μPIV confirming stratified flow and minimal reactant cross-over.

Conclusions:

• Herringbone flow promoters effectively enhance mixing and maintain reactant separation in microscale co-laminar flows.
• The study demonstrates a pathway to improved performance in membraneless microfluidic flow cells for electrochemical energy conversion.