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Flow Instabilities Associated With Impeller Clearance Changes In Stirred Vessels |
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| Authors: | C Galletti A Paglianti K C Lee M Yianneskis |
| Affiliation: | 1. Laboratory of Process Equipment, Department of Chemical Engineering , Industrial Chemistry and Material Science, University of Pisa , Pisa, Italy;2. Department of Chemical, Mining and Environmental Engineering , University of Bologna , Bologna, Italy;3. Experimental and Computational Laboratory for the Analysis of Turbulence , Division of Engineering, King's College London , London, U.K. |
| Abstract: | Flow instabilities associated with changes in the clearance (C) of a Rushton impeller from the bottom of a stirred vessel of diameter T?=?294?mm were studied experimentally with laser Doppler anemometry. It is shown that for C/T?=?0.17–0.18 flow changes from a double- to a single-loop pattern occur randomly. The transition from one regime to the other is characterized by periodic oscillations at a frequency (f) related to the impeller speed (N) by f/N?=?0.135. The lifetimes of the stable and unstable patterns were found to be affected by fluid density and viscosity as well as clearance. The implications of the results for both mixing processes in stirred vessels and related predictions of the flows are discussed. |
| Keywords: | Stirred vessel Transition Instability Impeller clearance |