Localized fluidization in granular materials: Theoretical and numerical study

Area of Science:

• Fluid dynamics
• Granular physics
• Multiphase flow

Background:

• Localized fluidization is a key phenomenon in granular materials.
• Understanding fluidization regimes is crucial for industrial applications.
• Previous studies identified homogeneous expansion, cavity, and chimney regimes.

Purpose of the Study:

• To investigate localized fluidization in granular layers with local fluid injection.
• To analyze the influence of injection rate and aperture size on fluidization regimes.
• To establish a link between fluidization regimes and inlet pressure dynamics.

Main Methods:

• Analytical approach at the continuum scale using Darcy's law and Therzaghi's effective stress principle.
• Numerical approach at the particle scale using coupled discrete element method (DEM) and pore-scale finite volume method (FVM).
• Comparison of analytical and numerical results with existing literature data.

Main Results:

• Three distinct fluidization regimes (homogeneous, cavity, chimney) were recovered as injection rate increased.
• Analytical methods accurately describe homogeneous porosity cases; numerical methods handle heterogeneous situations.
• Narrow apertures clearly distinguished the three regimes, while larger apertures led to homogeneous fluidization.
• Transitions between cavity and chimney regimes correlated with inlet pressure peaks for narrow apertures.

Conclusions:

• The occurrence of fluidization regimes is directly linked to normalized flux and aperture size.
• Numerical simulations provide more quantitative agreement with experimental data.
• A comprehensive understanding of localized fluidization regimes is achieved through combined analytical and numerical modeling.