Simulation of droplet size distribution of emulsions produced continuously using a vortex-based cavitation device: An ensemble approach based on CFD, PBM and ANN models

Emulsions find applications in varied industries like food and beverage, cosmetics and pharmaceuticals. Droplet size distribution (DSD) determines many critical quality attributes of an emulsion. An ability to simulate DSD is therefore pivotal to design devices for obtaining emulsions of desired DSD and properties. In this work, we present an ensemble approach for modelling the DSD of emulsions produced continuously using a vortex-based hydrodynamic cavitation (VD) device. The developed approach and computational models are evaluated by comparing the simulated results with the experimental data. Experiments on the continuous production of rapeseed oil in water emulsions (with Tween 20 as surfactant) were carried out at different operating parameters. The turbulent, three phase (gas-liquid-liquid) cavitating flow in a vortex-based cavitation device was simulated using the Eulerian approach. A population balance model with appropriate breakage kernels was developed and included with the computational fluid dynamics (CFD) model. The measured DSD was found to be bimodal, indicating two different breakage mechanisms (one based on turbulent shear and the other based on collapsing cavities). A novel methodology was developed to account for highly localised intense energy dissipation rates generated by collapsing cavities for simulating DSDs. The localised intense energy dissipation rates due to cavities were estimated using a previously developed artificial neural network (ANN). The predictions of DSD obtained with the developed methodology based on CFD, PBM and ANN showed good agreement with the experimental data. The presented approach and results will be useful for designing vortex-based cavitation devices for producing emulsions. The work will also provide a useful basis for developing multi-scale computational models for simulating the DSD of emulsions generated by hydrodynamic cavitation devices.