Alexander C Barbati
Particle transport in viscoelastic fluids is of paramount importance in a variety of biological and industrial processes. We consider the transport of rigid particles through a microscale expansion—contraction, and demonstrate that, at sufficiently high Reynolds (Re) and Weissenberg (Wi) numbers, particle accumulation occurs within the expansion—contraction region. We characterize our microchannel flows with a combination of particle image velocimetry of embedded tracer particles, streakline imaging, and direct observation of particle accumulation within the device. These methods show a narrowing of streamlines in the expansion—contraction, along with a qualitative change of the flow; Maps of flow parameter reveal that regions of extensional and rotational fluid motion in the expansion--contraction become regions of pure shear at large Reynolds and Weissenberg numbers, where particle accumulation occurs. Streakline imaging confirms the streamline narrowing, and further shows that a complex and unsteady 3D transport effect occurs. We posit that large normal force gradients in the flow cause the capture of particles in the expansion—contraction region. These on-chip experiments are accompanied by off-chip measurements of fluid rheology.