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Hysteresis and packing in gas-fluidized beds
1Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547, USA.
Summary
Hysteresis in gas-fluidized beds shows trivial scaling with particle size and aspect ratio, contrary to expectations. The packing fraction stabilizes at 0.590, irrespective of particle or container dimensions when gas flow is removed.
Area of Science:
- Fluidization dynamics
- Granular media physics
- Multiphase flow
Background:
- Gas-fluidized beds of granular media exhibit hysteresis in packing fraction and pressure drop during flow rate cycling.
- This hysteresis is theoretically linked to wall stress transfer, suggesting dependence on sample aspect ratio.
Purpose of the Study:
- To systematically investigate how hysteresis in gas-fluidized beds varies with particle size and sample aspect ratio.
- To determine if wall effects significantly influence hysteresis, challenging existing theories.
Main Methods:
- Conducted systematic measurements of hysteresis in gas-fluidized beds.
- Varied particle size and sample aspect ratio during experiments.
- Monitored packing fraction and pressure drop across fluidization transitions.
Main Results:
- Hysteresis demonstrated trivial scaling with particle size and aspect ratio, indicating minimal long-range wall effects.
- Measured packing fraction was consistently 0.590 ± 0.004 when gas flow was slowly removed.
- Packing fraction was found to be independent of particle size and container shape.
Conclusions:
- The observed trivial scaling of hysteresis suggests that wall effects are not dominant in gas-fluidized beds.
- The stable packing fraction of 0.590 provides a fundamental characteristic of granular media under specific de-fluidization conditions.
