[Paper Review] Experimental Investigation on Particle-Laden Flows of Viscoelastic Fluids in Micro-Channels Using Optical Coherence Tomography

Kasra Amini, Gustaf Mårtensson+2 more|arXiv (Cornell University)|Feb 25, 2023

Blood properties and coagulationMedicine3 citations

TL;DR

This study investigates particle migration in viscoelastic fluid flows within rectangular micro-channels using 2D depth-resolved Doppler Optical Coherence Tomography (D-OCT). The method enables simultaneous, high-resolution measurement of 3D velocity fields and particle tracking with sub-pixel accuracy, revealing non-uniform particle distribution due to elastic forces in polyacrylamide solutions (210–250 ppm), demonstrating OCT's capability to replace combined PIV and LPT systems for complex multiphase microflows.

ABSTRACT

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.

Motivation & Objective

• To investigate particle migration in viscoelastic fluid flows under non-uniform shear stress in micro-channels.
• To evaluate the feasibility and accuracy of using Optical Coherence Tomography (OCT) for simultaneous velocity field and particle tracking in complex multiphase flows.
• To replace conventional PIV and Lagrangian Particle Tracking (LPT) with a single, high-resolution OCT-based method for particle-laden viscoelastic flows.
• To quantify the spatial distribution of particles using Probability Distribution Functions (PDFs) to reveal underlying physics of particle migration.
• To demonstrate the capability of D-OCT to resolve velocity fields with sub-pixel accuracy and 2.58 µm depth resolution in microfluidic systems.

Proposed method

• Employed 2D Doppler Optical Coherence Tomography (D-OCT) for simultaneous, non-invasive imaging of 3D velocity fields and particle positions in micro-channels.
• Used polyacrylamide solutions (210 and 250 ppm) to induce viscoelasticity, creating non-Newtonian fluid behavior with elastic stresses.
• Achieved spatial resolution of 2.58 µm in the depth direction, enabling high-precision velocity field reconstruction.
• Applied sub-pixel image processing techniques to enhance particle position accuracy beyond pixel limits.
• Combined D-OCT velocity data with particle tracking to generate cross-sectional particle frequency maps.
• Calculated Probability Distribution Functions (PDFs) of particle positions across the channel cross-section to analyze migration patterns.

Experimental results

Research questions

• RQ1 How do viscoelastic stresses in polyacrylamide solutions (210–250 ppm) influence particle distribution in micro-channels?
• RQ2 To what extent does the non-uniform shear field in viscoelastic flows induce particle migration away from the centerline?
• RQ3 Can D-OCT accurately replace the combined use of PIV and LPT for measuring velocity fields and tracking particles in microfluidic systems?
• RQ4 What is the spatial distribution of particles across the channel cross-section, and how does it deviate from uniformity due to elastic forces?
• RQ5 How does sub-pixel image processing improve particle localization accuracy in OCT-based measurements?

Key findings

• D-OCT successfully captured 3D velocity fields with 2.58 µm depth resolution and sub-pixel particle positioning accuracy.
• Particle distributions in viscoelastic flows showed significant non-uniformity, indicating migration due to elastic normal stresses.
• The Probability Distribution Function (PDF) of particle positions revealed accumulation near channel walls, indicating lateral migration driven by viscoelastic forces.
• The method demonstrated equivalent or superior performance to combined PIV and LPT systems, eliminating the need for multiple measurement techniques.
• The use of polyacrylamide at 210–250 ppm induced measurable viscoelastic effects that altered particle dynamics in the micro-channel.
• The experimental setup enabled real-time, simultaneous acquisition of velocity and particle position data, enhancing data consistency and resolution.