  Considering the nonlinear response of non-Newtonian fluids to the local shear
exerted on the bulks of fluid, the initially quasi-uniform distribution of the
particles might be subject to alteration as well, due to the unbalanced force
distribution on the particles. The current research investigates such particle
migrations for flows of Viscoelastic Fluids (VEFs) in a straight micro-channel
with a 1 by 3.25 mm rectangular cross-section. Polyacrylamide polymer in
concentrations of 210 and 250 ppm have been used, where the heavy, linear,
long-chain structure of the polymer introduces elasticity to the fluid. The
flow measurements are performed using the state-of-the-art Optical Coherence
Tomography (OCT) in 2D acquisition and doppler modes (D-OCT) to simultaneously
resolve tomographic velocity field, and the transition of particles through the
monitored cross-sections. Through the implementation of the experimental method
in the current manuscript, the capability and convenience of using OCT for the
problem at hand are demonstrated, as the abovementioned obtained data were to
be equivalently captured by simultaneous use of Particle Image Velocimetry
(PIV), for the ambient medium velocity field, and Lagrangian Particle Tracking
(LPT) schemes, for identification and tracking the position of the particles.
The velocity field is obtained with the spatial resolution of 2.58um in the
depth direction, and through sub-pixel image processing, highly accurate
positioning of the particles is realized. The experimental results are then
used for statistical calculations, such as the Probability Distribution
Function (PDF) of the cross-sectional map of the space frequented by the
particles to explain the underlying physics.
