Characterizing regime transitions in a bubble column with internals

Abstract

AbstractEffects of internals on flow regimes are systematically investigated in a lab‐scale bubble column (BC) through six approaches: total gas holdup, drift‐flux, standard deviation, fractal analysis, chaos analysis and wavelet analysis. With increasing internals‐covered cross‐sectional area (CSA), these methods give various value of the first transitional superficial gas velocity, as different scales of structures are detected to characterize regime transition. While internals are found to have marginal effect on total gas holdup, significant change in gas‐holdup structure is discovered, showing a decrease in large‐bubbles holdup and an increase in small‐bubbles holdup in transitional and churn‐turbulent regimes. We propose a novel approach based on wavelet analysis to demarcate the boundaries among micro‐, meso‐, and macro‐scales. The energy fraction of these representative scales identifies two transitional velocities, suggesting that internals advance the advent of first transition and delay the second one. The operating window of transitional regime is, therefore, remarkably extended.