A lot of production processes involve mixing steps. The understanding of fluid flows in mixing processes of liquid components is needed in order to develop appropriate mixers for the chemical and pharmaceutical industry. Especially mixing in microfluidic systems is a challenge due to the diffusion-based processes. A multilamination micromixer with chessboard outlet geometry is used to induce the mixing process. To get comprehensive information about the mixing process, the velocity profile of the fluid flow and the species concentration distribution during the mixing process should be measured. Thus, we have combined particle image velocimetry (PIV) and Raman scattering. To enable rapid detection, the Raman imaging mode is used to visualise the concentration distribution. By this setup light sheets along and orthogonal to the outlet of the micromixer are recorded and synchronized with PIV measurement. As a model system we have used water and ethanol/methanol, enabling a selective monitoring of the substances by choosing appropriate spectral areas. The PIV is recorded based on Mie scattering and fluorescence using microsphere tracers. In this study, we present a setup for determination of the velocity profile field and the spatial concentration distribution of water and ethanol/methanol in a micromixer.

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Abstract. Two-dimensional Molecular-Tagging-Velocimetry (2D-MTV) has been used to investigate velocity fields of liquid flow in a micro mixer. Optical tagging was realized by using caged dye. For the first time patterns were generated by structured laser illumination using optical masks. This allows the generation of nearly any imaginable pattern. The flow induced deformation of the optically written pattern is tracked by imaging of laser induced fluorescence. Quantitative analysis of raw image series is carried out by novel "optical flow" based techniques. A comparison to the standard technique of µPIV has also been conducted. Additionally Planar Spontaneous Raman Scattering (PSRS) was applied in order to determine concentration fields for mixtures of ethanol and water.