Oscillatory flow of droplets in capillary tubes. Part 1. Straight tubes

The motion of fluid droplets in capillary tubes subject to the action of a mean pressure gradient and an oscillatory body force is studied via numerical computations. The effects of the oscillatory forcing on the bulk flow rate and on the droplet velocity are evaluated, and results are presented for a range of forcing conditions, fluid properties and drop sizes. For large droplets (whose undeformed diameter exceeds that of the capillary tube), significant enhancement in the bulk flow rate is observed when the drop capillary number is small and the oscillatory forcing is strong. The enhancement is associated with increased droplet deformation in the presence of oscillatory forcing. The dependence of the flow enhancement on the amplitude, frequency and waveform of the oscillatory body force is evaluated for a range of fluid properties.