(85c) The Dual Liquid-Solid Nature of Fluidized Granular Matter and Its Influence on Pattern Formation

The dual liquid-solid nature of fluidized granular
matter and its influence on pattern formation

Lilian de Martín (l.demartin@ucl.ac.uk), Kaiqiao Wu (kaiqiao.wu.13@ucl.ac.uk), and Marc-Olivier Coppens (m.coppens@ucl.ac.uk)

All from:

University College London

Department of Chemical Engineering

Torrington Place

London WC1E 7JE

United Kingdom

T + 44 20 7679 7369

F + 44 20 7383 2348

Granular beds
fluidized with an oscillating gas flow can form regular patterns under certain experimental
conditions. In a vertically quasi-2D bed, a row of bubbles with alternating
positions forms at every gas pulse, resulting in a triangular bubble
tessellation when viewed from the side of the bed. In a 3D bed, patterns
manifest themselves as stripe and square configurations on the surface of the
bed, similar to those observed in vertically vibrated granular layers and pure
liquids (Faraday waves). Patterns excel as a method to impose structure in
fluidized bed reactors, control the bubble size, and facilitate bed scale up,
but their formation mechanism is poorly understood.

Patterns in very
shallow¾few mm¾fluidized beds can appear with the entire bed operating in the
kinetic regime, i.e., with the solids packing below the critical packing limit,
whereas patterns in deeper beds typically appear with the bed operating in the
plastic regime, i.e., with the solids packing above the critical packing limit.
These two limit situations involve completely different physics and have deep
consequences for the computational modelling and the ability of different
approaches to capture this phenomenon [1]. In addition, the fact that vibrated
fluids and purely granular systems also form patterns under sinusoidal excitations
provides a unique framework to study the physics of granular matter.

In this
contribution, we discuss how pattern formation can be used to gain insight into
the liquid-solid dual nature of fluidized matter and provide some experimental
and computational examples of this duality.

[1] K. Wu, L. de
Martín, L. Mazzei, and M.-O. Coppens. Pattern formation in fluidized beds as a
tool for model validation: a two fluid model based study. Powder Technology
295, 35 (2016).