Kasra Amini presented at the Nordic Rheology Conference (NRC-2022), Reykjavik, Iceland “Experimental Investigation on Particle-Laden Flows of Viscoelastic Fluids in Micro-Channels Using Optical Coherence Tomography”


The introduction of particles to fluid flow is considered as a source of alterations in the viscosity-based behavior of the macroscopic flow field. The bilateral interactions between the solid particles and the fluid elements would both lead to changes in effective viscosity and, thereby, the velocity field. 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 1×3.25 mm² rectangular cross-section. Aqueous solutions of 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 rheological measurements are presented for the characterization of the viscoelastic behavior of the fluid samples, and the results are compared with similar flow conditions, however, in particle-laden glycerol flow as a Newtonian reference case. 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 2.58 µm 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.

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