144
6 Conclusions
and unstructured regimes. When excited by flows of varying velocity in the structured
regime, bubbles dynamically rearrange in predictable triangular lattices at different
levels of structuring. As expected, the homogeneity induced in the population of
bubbles, such as size, velocity and wavelength, is strongly correlated with the degreeof-order for the flow patterns created. Guided by the operating diagram, one can
easily reproduce a highly structured flow of bubbles in a pulsed bed and expect
tighter control over system behaviour, in comparison to a bubbling bed operated at
a constant flow.
To investigative the onset and stabilisation of pattern formation, Chap. 4 presented
computational modelling of experimentally structured beds using both EulerianEulerian and Eulerian-Lagrangian frameworks. Remarkably, the flows created under
the Eulerian-Eulerian model are capable of capturing the basic flow properties, but
fail to reproduce any feature of structured flows when the system is operated in
the structured regime. In contrast, a Eulerian-Lagrangian model correctly captures
the appearance of structured bubbles and reveals the periodic formation of dense
regions, which impedes solids movement and synchronises with the bubble nucleation. The contrasting simulated results highlight the ability of pattern formation to
represent a benchmark for validating implementations of multiphase flow models for
computational simulations of fluidisation phenomena.
With the successful modelling, Chap. 5 showed an analysis of the evolution of
bubbles in terms of the nucleation, propagation and rupture stages, as well as the solid
circulation for both the experimental and numerical patterned flows. For a highly
structured flow, the motion, position and growth of bubbles are predictable at any
phase angle of a pulse period and highly reproducible in time. Numerical structured flows become increasingly reproducible, as inter-particle friction increases,
demonstrating the stabilising effect of solid friction on pattern formation. When
interparticle friction is sufficiently large, the particle collisions become highly dissipative and dense regions emerge which rearrange bubbles and restrict the transversal
movements of solids at the bottom. As a result, macroscopic recirculation of solids
is suppressed in structured flows, but particles travel regionally alongside bubbles.
Accordingly, the system is compartmentalised into a set of locally controlled reactors
characterised by two length scales: bubble size and pattern wavelength, which are
correlated to the oscillation applied. Overall, dynamically structured flows form a
new type of gas-solid operation with highly controlled dynamics.
6 Conclusions
and unstructured regimes. When excited by flows of varying velocity in the structured
regime, bubbles dynamically rearrange in predictable triangular lattices at different
levels of structuring. As expected, the homogeneity induced in the population of
bubbles, such as size, velocity and wavelength, is strongly correlated with the degreeof-order for the flow patterns created. Guided by the operating diagram, one can
easily reproduce a highly structured flow of bubbles in a pulsed bed and expect
tighter control over system behaviour, in comparison to a bubbling bed operated at
a constant flow.
To investigative the onset and stabilisation of pattern formation, Chap. 4 presented
computational modelling of experimentally structured beds using both EulerianEulerian and Eulerian-Lagrangian frameworks. Remarkably, the flows created under
the Eulerian-Eulerian model are capable of capturing the basic flow properties, but
fail to reproduce any feature of structured flows when the system is operated in
the structured regime. In contrast, a Eulerian-Lagrangian model correctly captures
the appearance of structured bubbles and reveals the periodic formation of dense
regions, which impedes solids movement and synchronises with the bubble nucleation. The contrasting simulated results highlight the ability of pattern formation to
represent a benchmark for validating implementations of multiphase flow models for
computational simulations of fluidisation phenomena.
With the successful modelling, Chap. 5 showed an analysis of the evolution of
bubbles in terms of the nucleation, propagation and rupture stages, as well as the solid
circulation for both the experimental and numerical patterned flows. For a highly
structured flow, the motion, position and growth of bubbles are predictable at any
phase angle of a pulse period and highly reproducible in time. Numerical structured flows become increasingly reproducible, as inter-particle friction increases,
demonstrating the stabilising effect of solid friction on pattern formation. When
interparticle friction is sufficiently large, the particle collisions become highly dissipative and dense regions emerge which rearrange bubbles and restrict the transversal
movements of solids at the bottom. As a result, macroscopic recirculation of solids
is suppressed in structured flows, but particles travel regionally alongside bubbles.
Accordingly, the system is compartmentalised into a set of locally controlled reactors
characterised by two length scales: bubble size and pattern wavelength, which are
correlated to the oscillation applied. Overall, dynamically structured flows form a
new type of gas-solid operation with highly controlled dynamics.