(550j) Measurement of Droplet Coalescence in a Mixing Tank.

It is in urgent requirement to directly measure the droplet coalescence frequency for the application of the population balance model in accurately predicting the droplet size distribution. In this study, the coalescence events of droplet swarm in a mixing tank were directly recorded using a high-speed camera. Different types of coalescence including binary coalescence, ternary coalescence, quaternary coalescence and quintuple coalescence were discovered. The multiple coalescence was treated as a series of binary coalescences. The coalescence frequency was manually counted with the captured video. The effects of the rotating speed and holdup fraction on the droplet coalescence frequency was then quantitatively investigated. In order to further study the mechanism of coalescence, the droplet collision frequency was also counted and the coalescence efficiency was calculated. The models in literature were tested with our experimental data were found failing to predict the coalescence frequency, collision frequency, and coalescence efficiency in the stirred tank. Empirical correlations were finally proposed and good agreement was found between the prediction results and the experimental data.