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

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Principal Investigators
Hakan Basagaoglu
Hong Dixon
Shawn R. Allwein
Joe A. McDonough

Inclusive Dates:  07/01/07 – 12/31/09

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 particle transport analyses supporting safety and performance assessments of potential geological repositories where colloid-facilitated transport of radionuclides may be important. Such capabilities also are useful for optimizing targeted deliveries of engineered nano- or micro particles carrying reactive agents in biomedical and subsurface bioremediation applications.

Approach - This project focuses on developing two- and three-dimensional simulation capabilities to quantify the effects of physical, chemical, and hydrodynamic processes governing nano- or micro-scale particle migration in geometrically complex flow domains. The simulation capability is based on the lattice-Boltzmann (LB) method, which was chosen because of its computational efficiency and ease of handling complex flow domain geometries. The simulation capability was developed to analyze the effects of particle sizes and shapes, flow regimes, particle-wall interaction potentials, and particle and wall surface heterogeneities on particle trajectories in complex physical, chemical, and hydrodynamic flow systems. Because the proposed simulation capability involves developing and testing new modeling features such as channel wall-particle interaction potentials and the Brownian effect (stochastic or thermal fluctuations) for nano-sized particles, microscale laboratory experiments under different flow regimes need to be conducted for model validation and improvement.

Accomplishments - Computationally efficient two- and three-dimensional particle transport models based on the LB method have been developed to simulate trajectories of multiple inert or reactive particles and their immobilization on channel walls and obstacles. The models have been enhanced to include new simulation features involving (i) interparticle and particle-wall interaction potentials based on two-body van der Waals and electrostatic forces, and the harmonic-spring model, and (ii) fluctuating LB formulation to account for stochastic fluctuations in velocity of nanoparticles (which are not important for micro-sized particles). The model was validated using experiments in which the model correctly predicted trajectories, velocities, and hydrodynamic drifts of microparticles in microflow channels with staggered channel obstacles. Theoretical validations of the fluctuating LB model are currently in progress with funding from a San Antonio Life Science Institute (SALSI) grant. Theoretical validations revealed that the model accurately conserves thermal energy at the nanoscale; hence, the model is suitable for nanoparticle simulations. The model will be used to simulate trajectories and distribution of engineered capsules in vasculature tumor cells in mice experiments, as part of an ongoing SALSI project.

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