Wavelet Analysis of Particle Concentration Signals in an Acoustic Bubbling Fluidized Bed

The time series of fluid catalytic cracking (FCC) particle concentrations were measured by an optical fiber probe under conditions of different sound pressure levels and sound frequencies in an acoustic bubbling fluidized bed (? 140 mm × 1600 mm). The results show that the minimum fluidization velocity had a minimum value when the sound wave frequency was 150 Hz. Under the same sound frequency, the fluidization velocity decreased as the sound pressure level increased. The particle concentration signals in an acoustic fluidized bed were also analyzed by means of wavelet analysis. On the basis of discrete wavelet transform, an original signal was resolved into five detailed scale signals. By using wavelet energy analysis, it was found that the peak frequency of the scale 3 or 4 detail wavelet signals represents the bubbling frequency and the peak amplitude for the bubble size. The results indicate that the bubbling frequency and bubble size decreased with increasing sound pressure level at a given frequency. In addition they decreased with increasing sound frequency ranging from 50–150 Hz, but further increased with increasing sound frequency ranging from 150–500 Hz.