The effect of fluid flow on the detachment of drops in the wake of a flat plate

The pinch-off of liquid drops from the end of a flat plate has been studied. Gas flows parallel to the plate with mean velocity v, and creates a wake at the plate end. The break-up process is found to be reproducible, with the number of satellites increasing with both increasing velocity and increasing mass density. The diameter of the main drop after detachment, d, at Weber numbers exceeding 5 is found to be given byd/dv=0=1-CReplwith C = (5.6 ± 0.3) · 10−5 for ethanol and C = (2.9 ± 0.4) · 10−5 for water. The diameter in quiescent gas, dv = 0, is easily predicted, and Repl is the Reynolds number based on v and the thickness of the plate. Diameters at smaller Weber numbers are better predicted by a similar correlation in terms of the Weber number. Instantaneous acceleration and forces on a drop have been measured and analyzed. Hydrodynamic interaction between liquid and gas at high gas velocities at moments of strong interaction could be quantified with the usual expression for the drag force and a drag coefficient of about 1.3.