On the multi-dimensional microparticle fractionation in a sharp-corner serpentine microchannel

In this thesis, the multi-dimensional fractionation of particles smaller than 10μm with respect to their size and density is investigated inside a sharp-corner serpentine microchannel by means of experimental as well as numerical methods. The motivation for research on multi-dimensional particle fractionation methods is twofold. First, particles with highly specified characteristics are the basis for various products of several different industries. Second, due to environmental or sustainability requirements, particles with defined properties are targeted to be extracted from a bulk quantity. Passive microfluidic approaches have a large potential to provide such fractionation methods, due to their simplicity and parallelizability. One of these approaches is fractionation in sharp-corner serpentine microchannels. This approach is investigated in the present thesis. Long-exposure measurements are performed to investigate the general behavior of particles of several sizes and different densities at various bulk Reynolds numbers (chapter 4). Besides the confirmation of the high potential of the used method to fractionate micron sized particles with regard to their size, the results also reveal the potential to fractionate particles solely with regard to their density. Furthermore, it is demonstrated that the used method is suitable to focus sub-micron particles on distinct trajectories. The reconstruction of three-dimensional particle distributions additionally reveals that micron particles with different sizes and densities not only move on trajectories that are spatially separated in-plane, but also out-of-plane (chapter 5). Astigmatism Particle Tracking Velocimetry measurements also enable to determine a size fractionation performance of nearly 100%. To surpass qualitative descriptions of the force contributions that are relevant for the particle motion inside a serpentine microchannel, numerical simulations are performed (chapter 6). A detailed evaluation of the simulation results reveals that the contributions of the shear-gradient force and depending on the particle size also the drag force are dominant for the motion of a particle inside a serpentine loop under the investigated conditions. Moreover, a new extension of micro Particle Image Velocimetry is presented that provides the opportunity to measure the bulk dynamics of both phases of a suspension flow simultaneously (chapter 7). For this, a labelling procedure is used to create suspension particles with a ring-shaped particle image. A comparison with Gaussian and plateau-shaped particle images showed the superior characteristics of such ring-shaped particle images with respect to measurement accuracy