82
3 A Structuring Regime to Control Bubbling Beds
When one focuses on structured and highly structured flows, the wavelengths appear
proportional to the size of bubbles.
Such a coupling between size and separation is expected, as the visual inspection
shows that during each period, existing gas bubbles rise slowly, maintaining their
shape, without collapsing or moving laterally. The trailing bubbles in the next row
always nucleate from sites in between bubbles of the previous array. Bubble nucleation is, therefore, considered associating with its local solid circulation. Without
accessing into solid dynamics, it is difficult to interpret the solid-gas interplays in
close proximity to bubbles. Therefore, such a coupling phenomenon will then be
investigated later with the help of computational sights into the solid phase dynamics.
In addition, it can be noticed that structured flows only emerge in the left region of
the plot. Therefore, ratios of wavelength over bubble size are plotted as a function of
pattern intensity measured in beds of different heights, as shown in Fig. 3.24. A relatively large λ/D b ratio is found as a necessary condition for sustaining a highly structured flow. The ratio is observed increasing slightly with bed height. For beds deeper
than 5 cm, highly structured flow requires λ/D b > 2.5, in order to prevent bubble
interference and maintaining the propagation. For example, to capture a patterned
flow with Λ ~ 0.6, λ/D b is detected around 0.3 for 5 cm deep beds, while around 4.5
for 10 cm deep beds. Such a ratio is supposed to increase with bed height according
to Fig. 3.24c, d. Besides, there exist additional branches of λ/D b with a higher slope
for Λ ≤ 0.2 in Fig. 3.24b, c. Their occurrences are attributed to high-frequency
pulsations, such as f > 7 Hz, which generate quickly coalesced bubbles and enlarge
the pitch, yet the majority of bubbles retains in a relatively small size. The results
further support the existence of correlations between spatial separation and size of
bubbles.
Fig. 3.23 Correlation between bubble separation distance and bubble size in beds of G2 particles
under different pulsed flows and bed heights. Gray open circles stand for Λ ≤ 0.2, black filled
circles stand for 0.2 < Λ ≤ 0.4, and red filled circles stand for Λ > 0.4
3 A Structuring Regime to Control Bubbling Beds
When one focuses on structured and highly structured flows, the wavelengths appear
proportional to the size of bubbles.
Such a coupling between size and separation is expected, as the visual inspection
shows that during each period, existing gas bubbles rise slowly, maintaining their
shape, without collapsing or moving laterally. The trailing bubbles in the next row
always nucleate from sites in between bubbles of the previous array. Bubble nucleation is, therefore, considered associating with its local solid circulation. Without
accessing into solid dynamics, it is difficult to interpret the solid-gas interplays in
close proximity to bubbles. Therefore, such a coupling phenomenon will then be
investigated later with the help of computational sights into the solid phase dynamics.
In addition, it can be noticed that structured flows only emerge in the left region of
the plot. Therefore, ratios of wavelength over bubble size are plotted as a function of
pattern intensity measured in beds of different heights, as shown in Fig. 3.24. A relatively large λ/D b ratio is found as a necessary condition for sustaining a highly structured flow. The ratio is observed increasing slightly with bed height. For beds deeper
than 5 cm, highly structured flow requires λ/D b > 2.5, in order to prevent bubble
interference and maintaining the propagation. For example, to capture a patterned
flow with Λ ~ 0.6, λ/D b is detected around 0.3 for 5 cm deep beds, while around 4.5
for 10 cm deep beds. Such a ratio is supposed to increase with bed height according
to Fig. 3.24c, d. Besides, there exist additional branches of λ/D b with a higher slope
for Λ ≤ 0.2 in Fig. 3.24b, c. Their occurrences are attributed to high-frequency
pulsations, such as f > 7 Hz, which generate quickly coalesced bubbles and enlarge
the pitch, yet the majority of bubbles retains in a relatively small size. The results
further support the existence of correlations between spatial separation and size of
bubbles.
Fig. 3.23 Correlation between bubble separation distance and bubble size in beds of G2 particles
under different pulsed flows and bed heights. Gray open circles stand for Λ ≤ 0.2, black filled
circles stand for 0.2 < Λ ≤ 0.4, and red filled circles stand for Λ > 0.4