Development of Enhanced Three-Dimensional Simulation Capability for Analyzing the Migration of Colloids and Nanoparticles in Complex Flow Domains, 20-R9722

Principal Investigators
Hakan Basagaoglu
Shawn R. Allwein
Stuart Stothoff
Hong Dixon

Inclusive Dates:  07/01/07 – Current

Background - Existing continuum-based colloidal transport models use empirical effective
parameters to simulate various aspects of colloidal transport processes at a phenomenological
level. Such models do not adequately address the hydrodynamic processes governing particle
trajectories caused by channel-wall roughness, lubrication forces, and wall and inertial effects, nor
do they incorporate chemical and physical processes such as particle attachment on fracture-wall
surfaces caused by the Brownian effect and particle migration in geometrically complex flow paths. These processes, however, may significantly affect the retardation and migration paths of colloidal particles. Enhanced simulation capabilities would provide more reliable colloidal transport analyses supporting safety and performance assessments of potential geological repositories where colloid-facilitated transport of radionuclides may be important. Such capabilities are also useful for optimal design and delivery of reactive agents via engineered particles to targeted sites in biomedical and subsurface bioremediation applications.

Approach - A combined experimental and numerical analysis has been conducted to investigate migration paths and modes and retention kinetics of multiple inert or reactive micro-sized particles in geometrically complex microflow cells. A pore-scale numerical model based on the lattice-Boltzmann (LB) method has been developed to simulate experimental data generated in this project. The LB method was chosen primarily because of its computational efficiency and ease of handling complex flow cell geometries. The Lennard-Jones and electrostatic interaction potentials have been incorporated into the model to simulate particle-particle and particle-wall interactions. Microflow experiments have been conducted with (1) horizontal flow cells including channel-wall obstacles and (2) fractured-porous medium cells to study migration paths and modes and retention rates and locations of particles as a function of particle number concentrations, particle size, particle reactivity, flow rate, and cell geometry. An image analysis tool (using Matlab®) has been developed to calculate Lagrangian velocity statistics of particles from experimental data saved as movie files, and this tool is used to bridge experimental and numerical analyses.

Accomplishments - In the experimental and numerical studies, SwRI has successfully captured some well-established fundamental and some new or controversial microscale physicochemical processes. SwRI researchers experimentally and numerically simulated particle transport processes involving particle migration mode transitions. In general, there was good qualitative agreement between the experimental and numerical results. A sound theoretical foundation was developed, and researchers numerically demonstrated repulsion-induced particle entrapment and flow-field clogging in flow channels. Retention and multiple-ring accumulations of inert particles in slow-flow zones were observed experimentally as a function of particle concentrations and flow rates, which seem to be a controversial issue in the literature. Researchers also experimentally observed that particles traveling near obstacles in a horizontal flow channel drift gradually to the centerline as they pass around obstacles, propelled by the rapid acceleration near the obstacles, which is new in the literature. Detailed quantitative comparisons of the experimental data and numerical simulations are in progress.

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