Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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Identification of the Main Flow Regime Boundaries in Two Bubble Columns Based On a New Parameter Extracted from Gas Holdup FluctuationsNedeltchev, S. N.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.
The time series (60,000 points) of the cross-sectional averaged gas holdup in two bubble columns (0.15 and 0.4 m in ID) were measured by conductivity wire-mesh sensors. Both columns were equipped with perforated plate distributors (having an open area of 1 %). The sampling frequency was set at 2000 Hz. These data were used successfully for the flow regime identification. For this purpose a new parameter called maximum number of visits in a region Nvmax was introduced. Both bubble columns were operated with an air−tap water system at ambient conditions. The clear liquid height in both columns was adjusted at 2.0 meters. The wire-mesh sensors were installed at a height of 1.3 m above the sparger plates. The new dimensionless parameter Nvmax is based on a division of the signal’s range into different regions and the maximum number of signal visits in one of the regions. In both small and large bubble columns the Nvmax profiles exhibited two well-defined local minima, which identified two transition velocities Utrans. In the small column (0.15 m in ID), the two Utrans values were identified at 0.034 and 0.089 m/s, respectively. In the large column (0.4 m in ID) the first Utrans value remained the same, whereas the second Utrans value decreased slightly to 0.078 m/s. A comparison with the Kolmogorov entropy results and another dimensionless statistical parameter was also performed.
Contribution to proceedings
Second International Symposium On Multiscale Multiphase Process Engineering (MMPE-2), 24.-27.09.2014, Hamburg, Deutschland: Dechema, 42-47