The deformation and breakup of liquid drops in low Reynolds number flow through a capillary

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Abstract
The deformation and breakup of a freely suspended, immiscible liquid drop are examined experimentally for low Reynolds number flow in a straight circular capillary tube. Results are reported for capillary numbers from 0.05 to greater than unity and for values of the viscosity ratio that span more than three orders of magnitude. In every case, the size of the drop is comparable to the tube diameter. The steady‐state shapes of the drops are compared with previous numerical studies of the problem. However, for a critical value of the capillary number that depends on drop size and viscosity ratio, drop breakup is observed in the experiment. When the viscosity ratio is small, i.e., the drop fluid is less viscous than the outer phase liquid, an indentation in the trailing edge of the drop grows and entrains outer phase liquid inside the boundaries of the original drop. When the viscosity ratio is O(1), the drop stretches along the axis of the tube until it breaks.