Transient torque in stirred tanks

The transient dynamics of stirred tanks whose impeller speed undergoes smooth or step changes is investigated. First, a low-order model is developed, linking the impeller torque with the ‘extent’ of the solid-body rotation in the tank, derived from an angular momentum balance in a control volume aro...

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Bibliographic Details
Published in:Journal of fluid mechanics 2017-11, Vol.831, p.554-578
Main Author: Steiros, K.
Format: Article
Language:English
Subjects:
Angular momentum
Dynamics
Impellers
Mathematical models
Momentum
Ordinary differential equations
Reynolds number
Rotating bodies
Rotation
Tanks
Torque
Velocity
Vortices
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Summary:The transient dynamics of stirred tanks whose impeller speed undergoes smooth or step changes is investigated. First, a low-order model is developed, linking the impeller torque with the ‘extent’ of the solid-body rotation in the tank, derived from an angular momentum balance in a control volume around the impeller. Utilisation of this model enables the prediction of the torque ‘spike’ appearing after an impulsive change of the shaft speed, and of the torque evolution during a quasi-steady transition. For the case of a small impulsive change in the shaft speed, a characteristic spin-up time is also proposed. Torque measurements performed in an unbaffled stirred tank show considerable agreement with the theoretical predictions.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2017.652