An experimental investigation of the influence of electric field on the collision-coalescence of water drops

Abstract

Laboratory experiments were conducted on the collision-coalescence of pairs of water drops of equal size, in two oil media (kerosene and mustard), with and without external vertical electric field ( F ). The radii of the water drops used were in the range 1.6 to 1.7 mm and the external electric field varied from 0 to 375 V cm ?1 . Collision frequencies were determined for various combinations of mean lateral ( X ) and mean vertical ( Z ) separations of the drop pairs as fixed combinations of X and Z could not be reproduced in any given set of experiments due to the limitations of the mechanical set up of the apparatus. The collision frequency ( E ) for any given initial values of X and Z decreased with F up to a certain value of F and thereafter increased. The variations observed in the collision frequency under different external electric fields have been explained quantitatively based on the electrostatic theory of polarization charges. The vertical distance travelled by the pair of drops prior to a collision was less with the external electric field. For collision to occur at a fixed depth ( d ), the values of Z increased with F when X was zero. For the same initial conditions, collision took place earlier in kerosene than in mustard oil medium. The collision efficiency ( E x ), computed from the measured values of the radius of the collision-cross-sectional area, was less in the presence of external electric field. The drops did not coalesce without the external electric field. The coalescence frequency ( E c ) increased with F. The field values for 100% coalescence were lower in mustard oil as compared to those in kerosene. The path length between collision and coalescence events sharply decreased with increase of F . The collection efficiency was zero without external electric field and it increased with F . In the case where the collected drop was slightly smaller than the collector drop the collection efficiency was more compared to that when the drops were of equal size. DOI: 10.1111/j.2153-3490.1979.tb00906.x