Nonlinear time series analysis techniques were applied to characterise bubbling fluidization.
The experiments were carried out in a laboratory scale fluidized bed, operated under ambient conditions
and various sizes of particles, settled bed heights, measurement heights and superficial gas velocities. It
was found that a minimum in average cycle frequency, wide band energy and entropy with an increase
in the velocity corresponds to the transition between macro structures and finer structures of the
fluidization system. This minimum was mostly found in the macro structures of the bubbling
fluidization system. Hurst exponent of the pressure fluctuations showed that the fluidized bed has a
bifractal behaviour. The reciprocal of the break point in the Hurst profile is similar to the domain
frequency of the bed. The method of delays was used to reconstruct the state space attractor to carry out
analysis in the reconstructed state space. The state space reconstruction parameters, i.e., time delay and
embedding dimension, were determined and the results showed that their values are different for
various types of methods introduced in literature. Chaotic behaviour of fluidized system was
determined by introducing two nonlinear dynamic invariants, correlation dimension and entropy in
different ways. The state-space analysis reflected that a low dimension behaviour of the bubbling
fluidization system. The nonlinearity test showed that nonlinearity cannot be concluded at all gas
velocities.
Keywords: Nonlinear, pressure fluctuation, hurst exponent, chaotic attractor, entropy, correlation
dimension.
