Dynamic simulation of bimodal drop size distributions in low-coalescence batch dispersion systems

Transient drop size distributions in a batch stirred tank are a manifestation of the drop breakage and coalescence mechanisms. A recently developed experimental configuration using a laser diffraction technique suitable for on-line monitoring of drop size distributions, showed increased sensitivity in measuring the small diameter drops. For all experimental conditions tested it was observed that the batch low-coalescing dispersion system assumed characteristic bimodal distributions within very short agitation time. The laser diffraction technique revealed the fine changes of the small size peak of the distribution with sufficiently high resolution. The objective of the present study was to establish a breakage mechanism in order to predict the dynamic behaviour of the bimodal drop size distributions by using the population balance formalism. The proposed model considers breakage of the drops into one daughter and several satellite drops. The volume ratio between the generated drops as well as the number of satellite drops are considered to be proportional to the parent drop volume. The obtained agreement between the experimental and theoretical bimodal drop size distributions is quite satisfactory for a range of experimental conditions.