CFD simulation of the droplet size distribution of liquid‐liquid emulsions in stirred tank reactors

Abstract

Predicting the drop size distribution (DSD) is essential in particulate flows such as emulsions as it affects mass transfer and heat transfer. In the current work we developed a novel numerical method to account for droplet breakup. The droplet breakup relies on an in-house developed correlation which depends on the local shear rate and some fluid properties. Commonly, a population balance equation (PBE) is employed to describe the breakup and coalescence of the droplets; however, such an approach does commonly not distinguish between different slip velocities of the smaller and larger droplets. Therefore, we propose a hybrid modelling strategy, which combines an Eulerian-Eulerian two-fluid model (TFM) and a Lagrangian discrete particle model (DPM), which is referred to as the Hybrid TFM-DPM model. This method enables the efficient evaluation of the poly-disperse liquidliquid drag force form the local distribution of the different droplet diameters. The latter can be obtained by tracking statistically representative droplet trajectories for each droplet diameter class. Finally, we applied this novel approach to a liquid-liquid emulsion in a stirred tank presented. The results clearly show that the present method is able to predict the droplet size distribution for different rotational speeds of the stirrer