  Pair-collision between viscous drops in a confined shear is numerically
simulated to show that the confinement drastically alters the trajectories of
the drops. In contrast to free shear, drops here move towards the centerline
giving rise to a zero cross-stream separation and a net stream-wise separation.
The latter varies as inverse of capillary number and the cube of the
confinement (distance between the walls). The stream-wise separation does not
depend on the initial positions of the drops. An analytical theory for the
phenomenon is offered.
