The interaction and coalescence of liquid drops in flow through a capillary tube

The interaction between two liquid drops of unequal size suspended in low-Reynolds number flow through a capillary tube is studied experimentally. The sizes of the drops are comparable to the diameter of the tube. Conditions under which the interaction leads to coalescence of the drops are identified, and a time scale for coalescence to take place is measured. Results indicate that the interaction between drops leads to coalescence over a limited range of drop sizes that is strongly affected by the values of the capillary number and the viscosity ratio.