Multiscale characterization of nanoparticles in a magnetically assisted fluidized bed

Abstract Pressure fluctuations of a fluidized bed of nanoparticles were measured during the fluidization of nanoparticles with and without a magnetic field at a frequency of 50 Hz. Recurrence quantification analysis (RQA) and wavelet transform were used to determine the frequency range of various flow structures in the bed at three scales. The frequency ranges of the macro-, meso-, and micro-structures were determined to be 0–49 Hz, 49–781 Hz, and 781+ Hz, respectively. Comparison of the determinisms of the sub-signals with and without the external field revealed that in the presence the field, breakage of larger agglomerates occurs faster than re-agglomeration of small agglomerates into larger ones. The power spectral density function of the pressure fluctuations indicated that with an external magnetic field, the power and the frequency range of the pressure signal of macro-structures do not change noticeably. However, the power of the meso-structure signal increases and its frequency range is widened toward higher frequencies, confirming that the number of small bubbles and agglomerates increase in the bed. In addition, the energy of signal analysis indicated that the external field significantly increases the share of meso-structures in the bed, confirming the RQA results.