It is in urgent requirement to directly measure the droplet coalescence
frequency for the application of the population balance model. In this
study, a method was firstly developed to directly measure the droplet
coalescence frequency in turbulent flow field by using a specially
designed mixing tank and a high-speed camera. The effects of the
rotating speed and holdup fraction on the droplet coalescence frequency
was quantitatively investigated. The increasing of rotation speed
promotes first and then inhibits the coalescence, while the holdup
fraction has little influence on the coalescence frequency function. The
droplet collision frequency was also counted and the coalescence
efficiency was calculated. The models in literature were tested with our
experimental data and were found failing to predict the coalescence
frequency in the stirring tank. Empirical correlations were finally
proposed and good agreement was found between the prediction results and
the experimental data.