Characterization of hydrodynamics of bubble columns by recurrence quantification analysis

Bubble column reactors are nonlinear and chaotic systems and characterizing their hydrodynamics by linear methods does not offer appropriate information. Experiments were carried out in bubble column containing non-Newtonian shear thinning fluids with different viscosities. Three hydrodynamic structures (i.e., micro-scale, meso-scale and macro-scale) in bubble columns were detected. Frequency ranges corresponding to each structure was determined to be 0-6.25 Hz for macro-scale, 6.25-50 Hz for meso-scale and 50-200Hz for micro-scale. Effect of superficial gas velocity on size of bubbles was invetigated by analysis of pressure fluctuations using Recurrence Quantification Analysis (RQA). The RQA was used to determine transition velocities in the bubble column. The transition velocity from homogeneous to heterogeneous was in the range of 0.05-0.06 m/s in the low viscous solution and transition velocity from heterogeneous to slug flow in the range of 0.02-0.03 m/s for the high viscous non-Newtonian solution. (C) 2018 Elsevier Ltd. All rights reserved.