Length-based hydrodynamic fractionation of highly networked fibers in a mini-channel

Abstract Fractionation of cellulose fibers is performed within a circular mini-channel (diameter 7 mm) to realize a novel fractionation principle. We show that fractionation within a single-floc regime relies on the formation of a rigid network in cases where the crowding number is chosen to be greater than 60. Fractionation is performed for channel Reynolds numbersRe\mathrm{>}10,000, and unlike the situation in larger channels, fractionation is found to be relatively independent ofRe. Experiments show a high dependency of the radial aperture velocity and aperture width on fractionation performance associated with fibers that are longer than 200 µm. By contrast, fibers shorter than 200 µm are only influenced by the volumetric flow rate through the aperture. Our results suggest that fibers smaller than 200 µm are mobile in the near wall region. Fibers longer than 200 µm are, dependent on their length, drawn out of the network by hydrodynamic forces acting on them as a result of the radial fluid velocity caused by the accept flow through the aperture. Our results support a novel fractionation hypothesis that is in contrast to previous findings, which were based on dilute flows and were demonstrated in channels having a larger size.