Chapter 5
The Role of Solid Mechanics
in Stabilising Structured Flows
This chapter provides a detailed description of the self-organisation of bubbles into
triangular lattices in quasi-2D beds of glass beads fluidised under oscillatory flows
of varying frequency. The flow pattern is quantified experimentally by studying
the time evolution of the size, velocity and separation of bubbles. A comparative numerical study using discrete and continuum models reveals the stabilising
effect induced by interparticle friction. When the bed contracts, the bottom layer
of granules forms temporally locked regions that synchronise with the nucleation of
bubbles and stabilise flow structures. Due to the frictionless nature, classic continuum
models underpredict the energy dissipation and create a long-range, macroscopic
recirculation of particles, leading to a fundamentally different fluidisation state.
5.1 Introduction
The fundamental physics of fluidisation have attracted scientific interests for over a
century and yet, a firm grasp on the process control remains crucial for the operation, design and scale-up of gas-solid reactors. Over the last decade, it has become
clear that allowing for more degrees of freedom in a design stage gives rise to
elevated predictability. For instance, fluidisation can be enhanced by manipulating
the spatial distribution of particle-particle and particle-fluid interaction forces and/or
introducing time-dependent perturbations [10]. The latter provides a simpler, more
elegant, non-intrusive approach but it complicates greatly the dynamic by introducing the temporal dimension. Moreover, controlling bubble nucleation rates and
rearrangement is possible by manipulation of a pulsating gas flow. Previous works
[9, 22] and experiments shown in Chaps. 2 and 3 demonstrate that one can continuously modify bubble properties and structure bed hydrodynamics periodically via
adapting pulse frequency and amplitude. A set of controlled transport properties
can tackle many current industrial challenges e.g. addressing changes in feedstock,
process variables or yield, design and retrofit. More generally, the ability to gain
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. Wu, Dynamically Structured Flow in Pulsed Fluidised Beds, Springer Theses,
https://doi.org/10.1007/978-3-030-68752-6_5
115
The Role of Solid Mechanics
in Stabilising Structured Flows
This chapter provides a detailed description of the self-organisation of bubbles into
triangular lattices in quasi-2D beds of glass beads fluidised under oscillatory flows
of varying frequency. The flow pattern is quantified experimentally by studying
the time evolution of the size, velocity and separation of bubbles. A comparative numerical study using discrete and continuum models reveals the stabilising
effect induced by interparticle friction. When the bed contracts, the bottom layer
of granules forms temporally locked regions that synchronise with the nucleation of
bubbles and stabilise flow structures. Due to the frictionless nature, classic continuum
models underpredict the energy dissipation and create a long-range, macroscopic
recirculation of particles, leading to a fundamentally different fluidisation state.
5.1 Introduction
The fundamental physics of fluidisation have attracted scientific interests for over a
century and yet, a firm grasp on the process control remains crucial for the operation, design and scale-up of gas-solid reactors. Over the last decade, it has become
clear that allowing for more degrees of freedom in a design stage gives rise to
elevated predictability. For instance, fluidisation can be enhanced by manipulating
the spatial distribution of particle-particle and particle-fluid interaction forces and/or
introducing time-dependent perturbations [10]. The latter provides a simpler, more
elegant, non-intrusive approach but it complicates greatly the dynamic by introducing the temporal dimension. Moreover, controlling bubble nucleation rates and
rearrangement is possible by manipulation of a pulsating gas flow. Previous works
[9, 22] and experiments shown in Chaps. 2 and 3 demonstrate that one can continuously modify bubble properties and structure bed hydrodynamics periodically via
adapting pulse frequency and amplitude. A set of controlled transport properties
can tackle many current industrial challenges e.g. addressing changes in feedstock,
process variables or yield, design and retrofit. More generally, the ability to gain
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. Wu, Dynamically Structured Flow in Pulsed Fluidised Beds, Springer Theses,
https://doi.org/10.1007/978-3-030-68752-6_5
115