Addressing Gas Layer Absence in Eulerian Two-Fluid Bed Simulations

 Several factors can influence the presence or absence of a gas layer at the bottom of buried tubes in a Eulerian two-fluid fluidized bed simulation:

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* Minimum Fluidization Velocity: Ensure your gas inlet velocity exceeds the minimum fluidization velocity (Umf) for the specific particle size and shape used in your simulation. Below Umf, the gas won't have enough force to overcome interparticle forces, resulting in a dense packing of particles around the tubes.

 * Packing Arrangement: The initial packing of particles within the bed can affect gas distribution. Experiment with different packing techniques (e.g., random packing, close packing) to see if it influences gas holdup near the tubes.

 * Drag Models: The selection of drag models in your Eulerian two-fluid model can impact how the gas and solid phases interact. Try using different drag models (e.g., Schiller-Naumann, Syamlal-Obasi) to see if it affects the gas layer formation.

 * Boundary Conditions: Double-check the boundary conditions at the bottom of the bed. Ensure they allow for gas flow and aren't restricting gas from entering the region around the tubes.

 * Mesh Resolution: A finer mesh resolution near the tubes might better capture the gas-solid interaction and potentially resolve the formation of a gas layer.

If you've addressed these points and still encounter the discrepancy, consider consulting the specific literature you're referencing. Look for details on the simulation setup, drag models, and boundary conditions used by the authors. This might reveal additional insights into their model and potentially help you achieve similar results.

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More information on Eulerian two-fluid fluidized beds with buried tubes. Here are some additional aspects to consider:

 * Geldart Classification: The Geldart classification categorizes powders based on their fluidization behavior. Understanding your particle's Geldart regime (e.g., Geldart D for coarse particles) can provide clues on expected gas distribution patterns.

 * Computational Fluid Dynamics (CFD) Code: Different CFD codes might have slight variations in their Eulerian two-fluid model implementation. If possible, consult the software manual or user forums for specific recommendations regarding the code you're using.