Bubble characterization in the gas-solid fluidized bed using an intrusive acoustic emission sensor array

Bubble behaviors in fluidized beds were investigated by a self-designed double-core screened waveguide. Experiments presented that, the bubble dome and vortex would generate AE signals with different shapes when passing through the waveguide, which could be further used to precisely detect the bubble sizes and velocities both in pseudo-two-dimensional and three-dimensional fluidized beds. Compared with results from pressure fluctuations, bubble sizes measured by AE methods in three-dimensional fluidized beds were more consistent with empirical formulas results and displayed similar robustness. Furthermore, the measured bubble distributions demonstrated that bubbles tended to rise along an annular zone in the cross-section of the fluidized bed, and the annular zone shrank with the increasing height due to the net inward movement of bubbles. Under high gas velocities, the annular zone would shrink until reaching the centerline, while under low gas velocities, a steady annular zone existed at a certain radial position.