No abstract

The production of high‐quality liquid/liquid emulsions is a key factor in many industrial processes, such as in food or pharmaceutical industries. The premix emulsification process enables the controlled adjustment of fine and narrow distributed droplet sizes. Furthermore, premix emulsification in porous structures is considered a low‐shear process that enables the usage and formulation of shear sensitive media (e.g., proteins). However, the local and time‐dependent stress conditions and stress residence time at the droplet interface during droplet dispersion in micro‐porous structures are still unknown. In this paper, interfacial stress distributions during droplet dispersion in premix membrane emulsification are numerically (computational fluid dynamics, CFD) investigated. Time‐dependent stress conditions and stress residence times at the interface are calculated. The stress conditions are related to the droplet deformation process to identify the main mechanisms for droplet breakup. The results are compared to experimental analysis of the resulting droplet size distribution during emulsion formulation. It has been found that higher shear stresses occur at the pore wall, but lower shear stresses at the liquid/liquid (disperse/continuous) interface are responsible for the droplet dispersion process. The stress residence time shows that lower stresses are present over a longer time compared to higher stresses. This is relevant for the understanding of the dispersion process, but also for the use of shear sensitive media (e.g., proteins as emulsifier).

The objective of this research paper is to relate the influence of dynamic wetting in a liquid/liquid/solid system to the breakup of emulsion droplets in capillaries. Therefore, modeling and simulation of liquid/liquid flow through a capillary constriction have been performed with varying dynamic contact angles from highly hydrophilic to highly hydrophobic. Advanced advection schemes with geometric interface reconstruction (isoAdvector) are incorporated for high interface advection accuracy. A sharp surface tension force model is used to reduce spurious currents originating from the numerical treatment and geometric reconstruction of the surface curvature at the interface. Stress singularities from the boundary condition at the three-phase contact line are removed by applying a Navier-slip boundary condition. The simulation results illustrate the strong dependency of the wettability and the contact line and interface deformation.

The membrane emulsification process obtains the advantage to formulate liquid/liquid systems in a low shear stress process. Whereas the emulsification process and the influence of the membrane structure and geometry on the final product are well investigated, the liquid deformation and liquid dispersion process inside the membrane structure are quite unknown. In the present study, the droplet breakup mechanism in the vicinity of a solid wall is numerically investigated with OpenFoam using the Volume of Fluid Method. Different wetting conditions on the membrane wall have been implemented. The results show a relation between wetting properties and fluid dynamic disturbances' resp. instabilities that may grow to larger instabilities, resulting in droplet breakup inside the membrane. These results can be used to find the sweet spot of capillary driven droplet breakup with minimum shear force to handle shear sensitive media while keeping a defined mono disperse emulsion.