The effect of velocity on the coalescence of liquid drops impacting a liquid-liquid interface

The coalescence of tetrachloroethylene drops impacting a water-tetrachloroethylene interface at velocities up to 80 cm/sec was studied with high-speed conemaphotography in order to determine the effect of velocity on the coalescence process and to investigate the existence of rapid coalescence. A specially designed drop-forming nozzle was used to generate drops with independent variable and reproducible sizes and velocities in a highly contamination-free and vibration-free apparatus thermostated at 30.0 C. Two different modes of coalescence behavior could be distinguished by whether a drop bounced away from the interface after impact, either partially or completely losing contact, or maintained complete contact and oscillated with the interface. The existence of a critical velocity for rapid coalescence is discussed.