462912 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
University College London
Department of Chemical Engineering
London WC1E 7JE
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 . 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.
 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).