Influence of probe scale and analysis method on measured hydrodynamic properties of gas-fluidized beds

The multi-scale properties of gas-fluidized bed hydrodynamics are examined using three different sized optical probes in a two-dimensional fluidized bed of fluid cracking catalyst particles. It is shown that the probe scale determines the scale of structures reflected in the signals analyzed using Fourier and wavelet transformation methods. The conventional fast Fourier transform method failed to remove the noise inevitably present in experimental measurements, while a soft thresholding wavelet transform method was successful in minimizing the noise. The level of noise at superficial gas velocities between 2.5 and 6.2 cm/s is shown to be comparable, and formed a basis for setting the threshold values used in the soft threshold de-noising method. The probe scale, as well as the analysis method, influences the results, and thus the interpretation of experimental hydrodynamic data.