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Time series analysis of voidage signals in a bubbling fluidised bed

University of British Columbia

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.

Thesis/Dissertation

application/pdf

2009-06-16

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http://hdl.handle.net/2429/9354

Chemical and Biological Engineering

University of British Columbia

UBCV

DSpace