Bislug Flow in Circular and Square Cross-Sectional Microchannels

Liquid-liquid slug or bislug flow can occur in any cross sectional capillary tube that is wetting and has a low Bond number. When two immiscible fluids are in contact in a capillary tube forming three fluid-fluid interfaces, spontaneous flow may occur due to a pressure imbalance across the menisci. Flow traverses the tube towards the liquid with the higher surface tension. Bislug flow in both prewet and non-prewet channels has been investigated. The bislug velocity in the prewet channels is faster than those in the dry. The velocity increase can be attributed to the decrease in the energy loss associated with the moving contact line. There is a dramatic increase in flow velocity in prewet square channels where the fluid is wicked into the corners. This wicking action decreases the perimeter length of the advancing contact line thereby minimizing energy dissipation.