Flow Behavior of Nanoparticle Agglomerates in a Fluidized Bed Simulated with Porous-Structure-Based Drag Laws

Area of Science:

• Chemical Engineering
• Fluid Mechanics
• Materials Science

Background:

• Fluidized bed reactors are effective for nanoparticle synthesis due to scalability and large gas-solid contact.
• Nanoparticles form porous agglomerates (>90% porosity) that influence fluidization dynamics.
• The impact of agglomerate porosity on fluidized bed flow behavior remains poorly understood.

Purpose of the Study:

• To develop and evaluate a drag model that accounts for the porous structure of nanoparticle agglomerates.
• To investigate the influence of porous structures on the hydrodynamics of nanoparticle agglomerates in fluidized beds.
• To assess the suitability of porous-structure-based drag laws for Eulerian-Eulerian two-fluid models.

Main Methods:

• Developed a drag model incorporating porous-structure-based drag laws into the Eulerian-Eulerian two-fluid model.
• Conducted numerical simulations across particulate and bubbling fluidization regimes.
• Validated model predictions against experimental data for key fluidization parameters.

Main Results:

• Porous-structure-based drag laws, particularly for fractal porous spheres, showed better agreement with experimental data than solid sphere models.
• Accurate prediction of minimum fluidization velocity, bubbling velocity, bed expansion ratio, and agglomerate dispersion coefficient.
• Demonstrated the significant impact of pore structure on gas-solid flow behavior.

Conclusions:

• Porous structure significantly affects the gas-solid flow behavior of nanoparticle agglomerates in fluidized beds.
• Porous-structure-based drag laws are more appropriate for modeling nanoparticle agglomerate fluidized beds.
• The developed model enhances the understanding and prediction of nanoparticle synthesis and processing in fluidized beds.