Flow and dispersion through a close-packed fixed bed of spheres
1Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, United Kingdom.
Summary
This study simulates fluid flow in packed beds, revealing how stagnant zones impact tracer gas dispersion at low Reynolds numbers. At higher Reynolds numbers, flow becomes turbulent, enhancing dispersion and showing good agreement with experimental data.
Area of Science:
- Fluid Dynamics
- Computational Physics
- Chemical Engineering
Background:
- Understanding fluid flow and transport in packed beds is crucial for various industrial processes.
- The role of flow regimes and stagnant zones in dispersion is not fully elucidated.
- Previous studies often simplify the complex geometry of close-packed spheres.
Purpose of the Study:
- To investigate fluid flow and tracer gas dispersion in a face-centered cubic packed bed.
- To analyze the impact of Reynolds number on flow stability and dispersion characteristics.
- To compare numerical simulations with experimental data.
Main Methods:
- Numerical simulations using a lattice-Boltzmann formulation.
- Experimental investigation of tracer gas dispersion.
- Analysis of local kinetic energy distributions and particle trajectories.
Main Results:
- At low Reynolds numbers (Re ≤ 14), steady flow exhibits a power-law distribution of kinetic energies, highlighting the significance of stagnant zones.
- Higher Reynolds numbers lead to transitions to time-oscillatory and turbulent flows with a shift to a log-normal kinetic energy distribution.
- Turbulent flows show enhanced dispersion, with particle trajectories crossing symmetry planes and Fickian dispersion in the far field.
- Model predictions for chaotic flow (Re ≈ 100) align well with experimental results.
Conclusions:
- Stagnant zones significantly influence transport in packed beds at low flow rates.
- Flow transitions to turbulence enhance dispersion, a phenomenon accurately captured by the lattice-Boltzmann model.
- The study provides a validated numerical approach for predicting dispersion in complex packed bed systems.
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