| Summary: | The dynamics of voidage signals in bubbling fluidised beds are investigated both
experimentally and numerically. Experimental voidage signals were obtained by using an
optical fibre probe at different positions in a freely bubbling fluidised bed of diameter of
150 mm. Numerical simulated voidage signals were also predicted using the Cliff and
Grace bubble coalescence model.
Analysis of the experimental signals demonstrates that deterministic chaos can
arise in bubbling fluidised beds. Voidage signals collected at different geometrical
positions indicate that bubble size and frequency influence the chaotic characteristics of
the voidage signals. In the bottom, the voidage signals were generally more chaotic than
in the top section, while near the bed surface, with voidage signals becoming less chaotic
because of the bubble coalescence which has already occurred.
The numerical study used the three-dimensional version of the bubble coalescence
model to simulate optical probe signals in a gas-solid fluidised bed. These predictions
demonstrate that deterministic chaos can arise from non-linear bubble interactions in
bubbling fluidised beds. It is found that both bubble frequency and initial bubble size
influence the chaotic characteristics of the simulated voidage fraction signal, with bubble
frequency having a stronger effect than the initial bubble size.
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