Chaotic analysis of pressure fluctuations in a gas-solid fluidized bed

Abstract

The aim of the present work is to determine the superficial gas velocity range for which chaos occurs in a gas-solid fluidized bed for various static-bed-height to bed diameter ratios and sand/plastic-bead mixtures and to observe the change in deterministic chaos parameters. Four piezo-resistive pressure transducer along the height of fluidized bed have been used to record pressure fluctuations at 600 Hz. Amplitude Adjusted Fourier Transform (AAFT) technique has been used for generating surrogate data. Data have been analyzed for the superficial gas velocity range of 0 to 16 times the minimum fluidization velocity. For the various static bed heights and sand plastic-bead mixtures it is seen that chaos is observed in the superficial gas velocity range of 8 to 12 times the minimum fluidization velocity. The Hurst exponent rises with superficial gas velocity and then falls after a maximum. The change in the fractal dimension between surrogate and original time series also follows the same trend. The superficial velocity range for which chaos occurs is confirmed when there is change in fractal dimension between original and surrogate series greater than 0.55, Hurst exponent is above 0.5 and Lyapunov exponent is positive.