Development of Enhanced Three-Dimensional Simulation Capability for Analyzing the Migration of Colloids and Nanoparticles in Complex Flow Domains, 20-R9722Printer Friendly Version
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 due to 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 due to 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 also are useful for optimal design and delivery of reactive agents via engineered particles to targeted sites in biomedical and subsurface bioremediation applications.
Approach - The project focuses on developing a three-dimensional simulation capability to quantify the effects of physical, chemical, and hydrodynamic processes governing colloidal transport 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 will be used to quantify the effects of particle sizes and shapes, release locations and rates, 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 features such as channel wall-particle interaction potentials and the Brownian effect for small-sized particles, microscale laboratory experiments under different flow regimes will be conducted for model validation and improvement.
Accomplishments - Computationally efficient two- and three-dimensional colloid 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 model was upgraded by adding new simulation features involving (i) two-body van der Waals and electrostatic forces between particles; (ii) harmonic-spring model for particle attachments on channel walls and obstacles; (iii) immerse boundary model for simulating softer particle-wall interaction; and (iv) fluctuating LB formulation to account for stochastic behavior of particles. These modeling features are being tested. The first set of experiments was conducted using dilute and concentrated mixtures of micron-size microspheres and latex beads in fluid-filled microchannels with staggered wall obstacles under different flow rates. The experiments captured trains of particles crossing multiple streamlines in fast-flow paths and lagged particles in slow-flow paths. These observations are consistent with our numerical simulations. Numerical analyses of experimental data are in progress.