Universal stability curve for pattern formation in pulsed gas-solid fluidized beds of sandlike particles
Lilian De Martín (University College London)
C.P. Ottevanger (Student TU Delft)
J.R. Ruud van Ommen (TU Delft - ChemE/Product and Process Engineering)
Marc Olivier Coppens (University College London)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
A granular layer can form regular patterns, such as squares, stripes, and hexagons, when it is fluidized with a pulsating gas flow. These structures are reminiscent of the well-known patterns found in granular layers excited through vibration, but, contrarily to them, they have been hardly explored since they were first discovered. In this work, we investigate experimentally the conditions leading to pattern formation in pulsed fluidized beds and the dimensionless numbers governing the phenomenon. We show that the onset to the instability is universal for Geldart B (sandlike) particles and governed by the hydrodynamical parameters Γ=ua/(utφ) and f/fn, where ua and f are the amplitude and frequency of the gas velocity, respectively, ut is the terminal velocity of the particles, φ is the average solids fraction, and fn is the natural frequency of the bed. These findings suggest that patterns emerge as a result of a parametric resonance between the kinematic waves originating from the oscillating gas flow and the bulk dynamics. Particle friction plays virtually no role in the onset to pattern formation, but it is fundamental for pattern selection and stabilization.