The characterization of degree of turbulence and mixing in bubble columns is very important for the improvement of their performance. The three coordinates (radial, azimuthal and axial) of radioactive tracer particle (Sc-46) were measured by means of noninvasive Computer-Automated Radioactive Particle Tracking (CARPT) technique in four different cylindrical bubble columns (0.05, 0.10, 0.16 and 0.2 m in ID). The facilities were equipped with the same perforated plate distributor (82 holes, 0.4×10-3 m in diameter). The bubble columns operated with an air-water system at ambient conditions. Superficial gas velocities covering the range 0.02-0.12 m/s were examined.
The Kolmogorov entropy (KE) algorithm (Schouten et al., 1994) was applied to each coordinate's data in order to extract the degrees of chaos and turbulence in the column. It was found that the degree of turbulence decreased (lower KE values) with the column diameter enlargement. This means that the behavior of the gas-liquid system in the smaller columns is more chaotic and it is less predictable. The same result was obtained from all three coordinates of the radioactive tracer particle moving in the bubble bed.
The main transition velocity (marking the onset of transition regime) was identified by means of the KE algorithm applied to CARPT data and the effect of column diameter on this key parameter was investigated. The results were validated by means of two different entropies (KE and maximum information entropy). Based on the information entropy theory (Nedeltchev et al., 1999, 2000, 2003) the degree of mixing in each column was estimated and a comparison with the degree of turbulence was performed.
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