Capillary flow in microfluidic Hele-Shaw cells

Capillary flow in microchannels has received substantial attention of investigation recently due to its potential applications in microfluidics. This paper will report the new findings of capillary flow behavior in microfluidic Hele-Shaw flow cells. Flow cells with a rectangular cross section of 50×50, 50×500, 20×200, and 50×1000μm were used. It was observed that the shape of the meniscus varied with cell size and aspect ratio. The shape was also strongly affected by the contact lines on both sidewalls and the gas phase flow in front of the meniscus. For cells with same height, the meniscus was stretched more in the flow direction for wider cells. The measured averaged speed of the interface was 5.7, 8.3, 8.3 and ∼8 mm/s for the flow cells with a cross section of 50×50, 50×500 and 50×1000μm, respectively. The speed of interface movement was not affected significantly by the aspect ratio for the values used in the current study. The average speed for the flow cells agree reasonably well with the value from the theoretical analysis.