Droplet breakage in stirred dispersions. Breakage functions from experimental drop-size distributions

Abstract

Transient breakage drop-size distributions have been experimentally measured using an image analysis technique. The transient distributions show self-similar behavior. The breakage rate and daughter-drop distribution functions have been determined using an inverse-problem approach which takes advantage of this self-similarity. The inverse-problem results show that the breakage rate is not a power law function of the drop size. The breakage rate is found to increase sharply with the drop size and the stirrer speed while decreasing sharply with increase in the interfacial tension. It is also found to decrease with increase in the dispersed phase viscosity, though the dependence on the viscosity is weaker than on the other variables. The daughter drop distribution was found to be relatively insensitive to the stirrer speed and interfacial tension, but was found to depend on the dispersed phase viscosity. As the drop viscosity increases, the breakage becomes more erosive in nature, leading to a broader size distribution of daughter drops. Generalized correlations for the breakage rate and daughter-drop distribution which account for the effect of physical properties and experimental conditions are presented. These relations will be very useful in predicting the drop-size distributions in stirred dispersions. Models for the breakage functions are compared with those determined in this study and the model predictions of the transient-size distributions are compared with the experimental data.