Flow-induced particle migration in microchannels for improved microfiltration processes

Abstract

Microchannels can be used to induce migration phenomena of micron sized particles in a fluid. Separation processes, like microfiltration, could benefit from particle migration phenomena. Currently, microfiltration is designed around maximum flux, resulting in accumulation of particles in and on the membrane. In this paper it is shown that starting the design at the particle level will result in a new microfiltration process. The behaviour of suspensions between 9 and 38 volume% was studied by confocal scanning laser microscopy; migration as a result of shear-induced diffusion was observed in a rectangular microchannel with nonporous walls. Particles segregated on size within the first 10 cm of the channel. To illustrate this, at 20 volume% of small (1.53 μm) and large (2.65 μm) particles each, the larger particles migrated to the middle of the channel, while the small particles had high concentrations near the walls. The small particles could then be collected from their position close to the permeable walls, e.g. membranes, where the pore size of the membrane is no longer the determining factor for separation. Guidelines for using this phenomenon in a microfiltration process were derived and the selectivity of the process was experimentally evaluated. The small droplets could be removed from the mixtures with a membrane having pores 3.7 times larger than the droplets, thereby minimizing accumulation of droplets in and on the membrane. As long as the process conditions are chosen appropriately, no droplet deposition takes place and high fluxes (1.7 × 103 L h−1 m−² bar−1) can be maintained.