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Investigations on the stability of the flow characteristics in a bubble column

Lucas, D.; Krepper, E.; Prasser, H.-M.; Manera, A.


The role of the lift force for the stability of the homogeneous flow regime in a bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Such gradients may result from circulation cells in the bubble column as well as from local disturbances. Depending on the sign of the lift force such local disturbances in a homogeneous flow may be damped or enhanced. The corresponding feedback mechanism was analysed by means of a linear stability analyses. In the result criteria for stability were obtained for mono-dispersed flow, for a with two bubble size groups and finally with some additional approximations also for the case of N bubble size groups or a given bubble size distribution. In a next step the effects were investigated by CFD calculations. The obtained criteria for stability fit well together with the observed effects in CFD simulations. Recently two different groups confirmed the stability criteria experimentally.

Keywords: Bubble column; stabilty; lift force; CFD

  • Chemical Engineering & Technology 29(2006)9, 1066-1072