2.3 Results and Discussion
53
than in unstructured flows. Nevertheless, Fig. 2.20b shows that V b in the constant
fluidisation only increases from ~19.8 to ~20.7 cm/s, showing much less acceleration
in comparison to those in pulsed beds.
2.3.3 Influence of Structuring on Flow Properties
Pulsed beds are capable of generating a variety of flow patterns associating with
different flow properties, offering extra flexibility and controllability in the systems.
From the visual inspection on the bubble flows as well as the quantitative comparison
on number, size and rising velocity of bubbles above, it has shown that the manipulation on pulsed flow properties indeed effectively imposes control over bubbles
properties and alters the characteristics of bed hydrodynamics to a certain extent.
Such manipulation is not only restricted to an individual bubble, but also the collective arrangement of bubbles. As shown in the representative snapshots, the dramatic
difference in bubble arrangements allows one to visually distinguish self-organised
bubbles from chaotic bubbles. For examples, the snapshots in Figs. 2.9, 2.13 and 2.17
clearly demonstrate that the flow patterns created with oscillatory flows of F4–F8,
A1–A2 and B5–B7 rearrange in considerably regular forms. In addition to the flexibility induced by pulsation solely, it is reasonable to hypothesise that the emergence
of dynamic regular arrangement brings in extra effects on the collective properties
of bubbles.
2.3.3.1 Influence of Pulsation on Population of Bubble Size
The section examines the influence of pulsation on the characteristics of the bubble
size population. The bubble size population measured amongst pulsed flows of
different frequencies and amplitudes, as the representative examples, are compared.
Figure 2.21a, b display that the bubble size distributions measured are unimodal
and fairly symmetrical at the pulsed flows of B = 5 cm/s and A = 0.25. Compared
to the steady flow fluidised bed, relatively narrower dispersion is observed at the
pulse flow with a range of frequencies 4–8 Hz, where structured flows emerge. In
contrast, slightly border distributions are created at f < 4 Hz and f ≥ 8 Hz, as shown
in Fig. 2.21b, as these bubbles can not organise in any particular structure. Such a
phenomenon is understandable, as coalescence and breakups of bubbles are greatly
impeded at a patterned state. Moreover, further increasing pulse frequency does not
lead to either smaller bubbles or narrower distribution.
Increasing B gradually degrades structured flows into chaotic flows. Comparison
across the distributions in Fig. 2.21a, c, d demonstrates that the size distribution
becomes increasingly broader alongside degradation of structured flows. When the
acceleration increases from B = 5 to 7 cm/s, the bubbles still retain a relatively tight
size distribution with shifted peaks, showing an increase in bubble size. Nevertheless,
when increasing further to B = 11 cm/s, the flows degrade significantly into chaotic
53
than in unstructured flows. Nevertheless, Fig. 2.20b shows that V b in the constant
fluidisation only increases from ~19.8 to ~20.7 cm/s, showing much less acceleration
in comparison to those in pulsed beds.
2.3.3 Influence of Structuring on Flow Properties
Pulsed beds are capable of generating a variety of flow patterns associating with
different flow properties, offering extra flexibility and controllability in the systems.
From the visual inspection on the bubble flows as well as the quantitative comparison
on number, size and rising velocity of bubbles above, it has shown that the manipulation on pulsed flow properties indeed effectively imposes control over bubbles
properties and alters the characteristics of bed hydrodynamics to a certain extent.
Such manipulation is not only restricted to an individual bubble, but also the collective arrangement of bubbles. As shown in the representative snapshots, the dramatic
difference in bubble arrangements allows one to visually distinguish self-organised
bubbles from chaotic bubbles. For examples, the snapshots in Figs. 2.9, 2.13 and 2.17
clearly demonstrate that the flow patterns created with oscillatory flows of F4–F8,
A1–A2 and B5–B7 rearrange in considerably regular forms. In addition to the flexibility induced by pulsation solely, it is reasonable to hypothesise that the emergence
of dynamic regular arrangement brings in extra effects on the collective properties
of bubbles.
2.3.3.1 Influence of Pulsation on Population of Bubble Size
The section examines the influence of pulsation on the characteristics of the bubble
size population. The bubble size population measured amongst pulsed flows of
different frequencies and amplitudes, as the representative examples, are compared.
Figure 2.21a, b display that the bubble size distributions measured are unimodal
and fairly symmetrical at the pulsed flows of B = 5 cm/s and A = 0.25. Compared
to the steady flow fluidised bed, relatively narrower dispersion is observed at the
pulse flow with a range of frequencies 4–8 Hz, where structured flows emerge. In
contrast, slightly border distributions are created at f < 4 Hz and f ≥ 8 Hz, as shown
in Fig. 2.21b, as these bubbles can not organise in any particular structure. Such a
phenomenon is understandable, as coalescence and breakups of bubbles are greatly
impeded at a patterned state. Moreover, further increasing pulse frequency does not
lead to either smaller bubbles or narrower distribution.
Increasing B gradually degrades structured flows into chaotic flows. Comparison
across the distributions in Fig. 2.21a, c, d demonstrates that the size distribution
becomes increasingly broader alongside degradation of structured flows. When the
acceleration increases from B = 5 to 7 cm/s, the bubbles still retain a relatively tight
size distribution with shifted peaks, showing an increase in bubble size. Nevertheless,
when increasing further to B = 11 cm/s, the flows degrade significantly into chaotic