Mesoscale modeling of emulsification in rotor-stator devices

Precise and rational control of droplet size distribution (DSD) is important in emulsification for target-oriented product design. To develop a complete DSD model, crossing the two mesoscales of two different levels is of great significance, viz., the emulsifier adsorption at interfacial level (Mesoscale 1) and the droplet breakage and coalescence in turbulence in rotor-stator device level (Mesoscale 2). While the first mesoscale can be simulated by coarse-grained molecular dynamic (CGMD), the second has been investigated in computational fluid dynamics and population balance model (CFD-PBM) simulation through the Energy-Minimization Multi-Scale (EMMS) approach in Part I. We then developed a model framework in Part II, coupling CGMD and CFD-PBM simulation through surfactant transport equations in bulk phase and at interface, with source terms taking account of emulsifier adsorption parameters. The parameters including maximal adsorption amount, diffusion coefficient and adsorption/desorption kinetic constants are acquired from CGMD. The coalescence efficiency is then corrected by the interfacial area fraction not occupied by surfactant and fed into the coalescence kernel functions in PBM. Compared to traditional CFD-PBM simulation, the coupled model can greatly improve the simulation of DSD, Sauter mean diameter, median diameter and span for high dispersed phase amount (DPA), and correctly reflect the influence of DPA, surfactant concentration and rotational speed of rotor-stator (RS) devices. While the simulation cases validate and demonstrate the advantage of this new model framework, it is also promising to incorporate different types of surfactant in future.