Dynamic behavior of the flow field of a bubble column at low to moderate gas fractions

Citation
Rf. Mudde et Hea. Van Den Akker, Dynamic behavior of the flow field of a bubble column at low to moderate gas fractions, CHEM ENG SC, 54(21), 1999, pp. 4921-4927
Citations number
19
Categorie Soggetti
Chemical Engineering
Journal title
CHEMICAL ENGINEERING SCIENCE
ISSN journal
00092509 → ACNP
Volume
54
Issue
21
Year of publication
1999
Pages
4921 - 4927
Database
ISI
SICI code
0009-2509(199911)54:21<4921:DBOTFF>2.0.ZU;2-C
Abstract
Time series of the vertical component of the liquid velocity in a bubble co lumn of 15 cm diameter have been obtained using LDA. The sets were measured close to the wall at h/D = 3.3. The ungassed height was H-0/D = 8; the gas fraction ranged from 0.4 to 18%. Each time series had a length of 900 s an d a number of data points between 220 and 300 k. The series were analyzed u sing a multiresolution analysis based on the Haar-wavelet. The standard dev iation of the low-frequency parts of the multiresolution decomposition was found to tend towards a non-zero value that is independent of the gas fract ion if the decomposition level increases. This suggests that the low-freque ncy oscillations are universal. They are probably caused by the meandering of the bubble clusters and the motion of vortical structures. The analysis shows that the changes in the liquid flow field are rather smooth when incr easing the gas fraction. If a transition from one regime to another is to b e identified, it is located around gas fractions as low as 1%. This conclus ion is supported by analysis of the same signals based on auto-regressive m odeling. (C) 1999 Elsevier Science Ltd. All rights reserved.