Application of Chaos Analysis for the Investigation of Turbulence in Heterogeneous Bubble Columns

Abstract

The Kolmogorov entropy (KE) algorithm was applied to local gas holdup fluctuations for estimating the degree of turbulence (chaos) in a large-scale bubble column (0.289 m ID and clear liquid height: 1.31 m). The latter was operated with nitrogen and polyalphaolefin liquid (PSS8) in the churn-turbulent regime (0.117 ≤ U g ≤ 0.257 m/s) at both high temperature (T = 441-468 K) and pressure (P = 1.8-2.5 MPa). Measurements in four different zones (z = 0.35, 0.67, 1.1 and 1.52 m) were performed. When the bubble coalescence is weak (local gas holdups < transitional gas holdup), the KE exhibits an initial peak (enhanced turbulence) in the first zone, then a sudden drop in the second zone and finally it increases smoothly in the upper zones. In the case of strong bubble coalescence, the KE exhibits alternating maxima and minima, i.e., instable flow patterns. It was found that at z = 1.52 m, the KE values increase with P. At higher values of T, the KE values are lower in all zones.

Applications of tomography in bubble column and trickle bed reactors

“…CT techniques have been used to characterize changes in the flow structure from different sparger designs (Ong et al, 2009;Varma & Al-dahhan, 2007), internals (Chen, Kemoun, et al, 1999;Chen, Li, et al, 1999) and composition (Hubers et al, 2005;Patel & Thorat, 2008) and have also been explored as a means to characterize the flow regime using ideas from chaos analysis (Nedeltchev, 2009;Nedeltchev et al, 2006Nedeltchev et al, , 2007. However, these studies have been limited to time-averaged measurements owing to the long time taken to acquire conventional CT measurements.…”

New Evidence for the Mixing Length Concept in a Narrow Bubble Column Operated in the Transition Regime

“…The turbulence intensity is also of essential importance since it has a pronounced influence on the local transfer rate. In the bottom region (close to the gas distributor) the turbulence intensity is higher than in the rest of the column (Nedeltchev, 2009). At high superficial gas velocities U G the liquid phase is highly turbulent throughout the bubble bed.…”