Direct measurements of small water coalescence droplets in efficiency and frequency an electric field

Small water droplets with diameter d ≤ 8 μm are allowed to fall in a settling chamber in the presence of a quasi-uniform electric field varying from zero to 600 V/cm. The trajectories of these droplets are photographically recorded through an incident-light microscope with dark field illumination. Results from 2 000 photographs, each one containing about 25 droplet pairs, show that the coalescence efficiency is almost unity. The coalescence frequency is almost zero in the absence of an electric field and increases rapidly at fields stronger than 400 V/cm. The coalescence frequency increases about linearly with electric fields from 100 to 400 V/cm. A survey of coalescences of droplets with parallel trajectories gives some order of magnitude for the collision efficiency, which indicates that the influence of the electric field is very pronounced for small droplets.