Resolution of structure characteristics of passive acoustic emission signals in multiphase flow system

The underlying structure characteristics of acoustic emissions (AE) measured in a gas-solid fluidized bed was investigated detailedly by resorting to wavelet transform and rescaled range analysis. A general criterion was proposed to resolve AE signals into three characteristic scales, i.e. micro-, meso- and macro-scale, and a so-called 'structure diagram' was introduced. Compared with the structure diagram of pressure signals, it was found that AE signals in micro-scale reflect mainly the particles motion while pressure signals in meso-scale reflect mainly the bubbles motion. Energy distribution analysis further revealed that the most energies in AE and pressure signals were distributed mainly by the micro-scale and meso-scale signals respectively. Moreover, the structure characteristics of AE signals collected from gas-solid fluidized bed and liquid-solid stirred tank were compared based on structure diagram and energy distribution analysis. The results indicated that although the same measurement technique was adopted, the structure characteristics of AE signals measured in gas-solid fluidized bed and liquid-solid stirred tank still exhibited larger difference. As an illustrative application of AE technique in process monitoring, a prediction model for particle size distribution was proposed and the satisfactory results were obtained both for laboratory scale and plant scale fluidized beds.