Developing Acoustic Emission Techniques to Characterize Particle-Gas Flows

The characterization of particles in solid-gas flows is of great importance in many industrial sectors such as nuclear energy and pharmaceuticals industries. Acoustic techniques can provide non-intrusively, multi-point measurements in non-transparent systems and can complement other techniques e.g., optical sensors, x-ray. In this work, acoustic emission (AE) techniques are applied to the study of gas-solid fluidized beds. The experimental setups, measurement method and signal processing methodology of the acoustic emission signal for obtaining particle size distribution, particle velocity in solid-gas fluidized bed are discussed. The experiments were conducted in a vertical tube with a 14 cm inner diameter, made of borosilicate glass, that contains 2 kg glass particles with density of 2500 kg/m³. The AE signals were measured experimentally for different particle sizes ranging from 100 μm to 1 mm. The measurement technique is based on the measurement of signal frequency, energy and root mean square (RMS) of the generated acoustic emission signal, to obtain particle velocity and particle size in the solid-gas flows. The results indicated that the acoustic emission features, root mean square RMS and energy of the AE are related to the change in gas superficial velocity and particle size, while the frequency of the generated AE signal is related to the particle size. A theoretical model is proposed for the generation of acoustic emission from the collision of particles with reactor wall. This study indicated that the AE features have great potential in the application of gas-solid flows.