Flow regime identification in a three-phase bubble column based on statistical, Hurst, Hilbert-Huang transform and Shannon entropy analysis

Flow regime transitions in a gas-liquid-solid three-phase bubble column were investigated based on pressure time series. The statistical, Hurst, Hilbert-Huang transform and Shannon entropy analysis methods were applied to differential pressure fluctuation data measured in a two-dimensional (2-D) bubble column measuring 0.1 m in length and 0.01 m in width equipped with a sintered plate distributor (average diameter of holes was 50 μm). Air was used as the gas phase and tap water as the liquid phase. Glass beads measuring 150 μm in size with a particle density of 2500 kg/m3 constituted the solid phase. Based on sudden changes in both the EMD energy entropy from Hilbert-Huang transform and the Shannon entropy values, two flow regime transition gas velocities were successfully identified: the homogeneous regime shifted to the transition regime at a superficial gas velocity of 0.069 m/s; and the transition regime shifted to the heterogeneous regime at a superficial gas velocity of 0.156-0.178 m/s. The transition gas velocities showed good agreement with the experimental results. The EMD energy entropy and Shannon entropy analysis methods can reveal the complex hydrodynamics underlying gas-liquid-solid flow and are confirmed to be reliable and efficient as non-invasive methods for detecting flow regime transitions in three-phase bubble column systems.