Data on the rate of rise and distortion of drops in several liquid-liquid systems have been collected. These are compared with correlations developed by other investigators, and in some cases discrepancies between observed and predicted values are noted which do not seem to be related to any easily measured physical property. However evidence is given showing that they are most likely due to the presence of surface-active materials. Photographs and shadowgraphs showing the nature of the flow around and behind moving drops are also included. The point of boundary-layer separation on the drop surface as indicated by these photographs has been related to the internal drop circulation. It is the shift in this point of separation which is the primary cause for the reduction in drag of liquid drops as compared with solid spheres. A previous theory for the breakup of rain drops explains the existing data for drop breakup in liquid-liquid systems.
SUMMARY OF EXPERIMENTAL PROCEDURE
Details of the equipment used in this investigation have been presented elsewhere ( 1 ). Briefly it consisted of a vertical test chamber 6 in. sq. and 2 ft. high. The front and back sides of this test section were made of glass, permitting visual and photographic observations. The continuous phase was maintained at a constant temperature by circulating it through an external heater and moved countercurrent to the drops at a rate which was small compared with the drop velocity.