Single fiber transport in a confined channel: Microfluidic experiments and numerical study

We present an experimental and numerical study on the transport of a single fiber confined in a microfluidic Hele-Shaw geometry. The fiber has a square cross-section and a typical aspect ratio of ten. We address the question of the fiber velocity as it is freely transported by the flow, and study in particular its dependence on the fiber orientation and confinement in the channel, defined as the ratio of the fiber height with the channel height. Both experiments and simulations are set so that the fiber suspended in the middle of the channel height does not interact with the lateral flow boundaries. At low confinements, the fiber velocity is independent of the fiber orientation with the flow direction and tends to the maximal velocity of the fluid when the confinement tends to zero. The fiber slows down as the confinement increases. We find that as the confinement reaches approximately 0.5, the orientation affects the fiber velocity: a fiber perpendicular to the flow direction moves faster than a parallel one. Consequently, a confined fiber transported in a microchannel at an angle different from 0 degrees or 90 degrees with the flow direction will drift towards a lateral wall, in the opposite direction found in sedimenting fibers. We also characterize the perturbation caused by the presence of the fiber on the flow field, and find that it drops very quickly as the fiber confinement decreases. (C) 2013 AIP Publishing LLC.