Snap-off of gas bubbles in smoothly constricted noncircular capillaries

Abstract A corner flow hydrodynamic theory is outlined for the time to snap‐off of a gas bubble moving through a smoothly constricted noncircular capillary as a function of the pore geometry and the capillary number, Ca . Above a transition capillary number the time to snap‐off is independent of Ca , while below it the time to snap‐off is inversely proportional to the capillary number. Thin films of liquid deposited along the capillary walls are shown to play a minor role; they are accordingly neglected in the analysis. The proposed theory is compared to new experimental results for snap‐off in two constricted square capillaries (dimensionless constriction radii of 0.3 and 0.5) over a range of capillary numbers (10 −5 to 10 −3 ), wetting‐liquid viscosities (1.0 to 8.5 mPa · s), and surfactant types. Good agreement is found between theory and experiment.