The acoustic emission (AE) signal characteristics were measured under different inlet gas velocity of gas solid fluidized bed. The hydrodynamics of the bed and the transition velocity from bubbling to turbulent fluidization were investigated by acoustic energy and recurrence quantification analysis (RQA). Because the acoustic energy analysis could not distinguish the regime transition velocity at different bed height

RQA was further applied to analysis the acoustic signals due to its ability to predict periodicity of a system. The results of RQA indicated that the motion of solids was more periodic when the bed was at the bubble regime compared to the turbulent regime. And the transition velocity of the solids at the lower bed height calculated by RQA was higher than that at the higher bed height. Therefore

the acoustic emission technique based on RQA should be an effective way to monitor the transition of flow regimes in the gas-solid fluidized bed and indicate the process of regime transition at different bed heights.