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.
Flow instabilities associated with impeller clearance changes in stirred vessels
GALLETTI, CHIARA;
2005-01-01
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
