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On the application of LDA to bubbly flow in the wobbling regime (1999)

Groen, J. S. ; Mudde, R. F. ; Van Den Akker, H. E. A.

Springer

Experiments in fluids 27 (1999), S. 435-449

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ISSN: 1432-1114

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Considerations for applying LDA to bubbly flows with bubbles about 3 to 4 mm in diameter were investigated by means of detailed experiments in the model geometry of a train of bubbles. Both forward scatter and backscatter LDA were studied. The validity of phase discrimination via burst amplitude was tested and special attention was paid to the impact of bubble interface response to the laser beams. Forward and backscatter measurements can be compared well. In both configurations, predominantly the liquid phase is “seen” by LDA. A bubble itself only leads to a velocity realization in special conditions. In those cases the Doppler shift is determined by the motion of the bubble interface which consists of the motion of the center of gravity of the bubble as well as shape oscillations. In backscatter bubbles only give velocity realizations when their “cheeks” pass through the measuring volume virtually perpendicularly. It is shown that the bubble-caused velocity realization frequency is very low for bubbles of the size used. Phase discrimination on burst amplitude does not hold. In ambient cases such as bubble columns one can assume that only the liquid phase is being studied.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003480050369

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Role of coherent structures on reynolds stresses in a 2-D bubble column (1997)

Mudde, R. F. ; Lee, D. J. ; Reese, J. ; [et al.]

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 43 (1997), S. 913-926

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ISSN: 0001-1541

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology

Notes: The hydrodynamics of two-dimensional bubble columns operated in various flow regimes are studied using particle image velocimetry. Both averaged velocity profiles and Reynolds stress profiles are obtained and discussed in relation to large-scale structures present in the flow. The normal stresses, dominated by large-scale structures, are an order of magnitude higher than the shear stress. It is found that the contribution from the bubbles to the shear to the normal stresses is negligible. A time series of the flow field is studied, demonstrating that the flow could be split into a low-frequency contribution due to the vortical structures and a high-frequency fluctuating part. The latter gives rise to flat normal stress profiles, and the former is responsible for the original form of the normal stress profiles. The shear stress in the smaller columns investigated can be related to the averaged vertical velocity profile according to a Boussinesq approximation. Data on the eddy viscosity are presented.

Additional Material: 21 Ill.