Mixing and emulsification processes in micromixers

Mixing and emulsification processes in micromixers developed by the Institute of Microtechnology Mainz (IMM) are investigated by means of computational fluid dynamics (CFD). For both miscible and immiscible fluids the CFD results are compared to experimental data obtained with transparent micromixer made from photosensitive glass. It is found that in the case of miscible liquids the accuracy of numerical predictions is limited by artifacts from numerical diffusion. However, streamline tracking techniques offer an alternative method for computing flow patterns in micromixers. Corresponding flow patterns comply with photographic images of the mixing zone. Subsequently, the case of immiscible liquids is investigated using volume tracking techniques. The simulations, based on a 3D model for a planar interdigital micromixer, describe the time evolution of droplet formation. Data on droplet size and the decay wavelength of the liquid lamellae are in agreement with experimental results. Both the simulations and the experiments indicate that surface tension forces play the dominant role for droplet formation. Thus, the results suggest that even in the presence of wall boundaries and shear forces the Rayleigh-Plateau instability governs the dynamics.