Abstract

Experimental data obtained by measuring the tangential component of force affecting radial baffles in a flat-bottomed cylindrical mixing vessel stirred with pitched blade impellers is analysed. The maximum mean tangential force is detected at the vessel bottom. The mean force value increases somewhat with decreasing impeller off-bottom clearance and is noticeably affected by the number of impeller blades. Spectral analysis of the experimental data clearly demonstrated the presence of its macro-instability (MI) related low-frequency component embedded in the total force at all values of impeller Reynolds number. The dimensionless frequency of the occurrence of the MI force component is independent of stirring speed, position along the baffle, number of impeller blades and liquid viscosity. Its mean value is about 0.074. The relative magnitude (QMI) of the MI-related component of the total force is evaluated by a combination of proper orthogonal decomposition (POD) and spectral analysis. Relative magnitude QMI was analysed in dependence on the frequency of the impeller revolution, the axial position of the measuring point in the vessel, the number of impeller blades, the impeller off-bottom clearance, and liquid viscosity. Higher values of QMI are observed at higher impeller off-bottom clearance height and (generally) QMI decreases slightly with increasing impeller speed. The QMI value decreases in the direction from vessel bottom to liquid level. No evident difference was observed between 4 blade and 6 blade impellers. Liquid viscosity has only a marginal impact on the QMI value.

Highlights

  • Liquid flow in mechanically stirred vessels has been studied intensively on recent decades

  • The technique is based on a combination of spectral analysis with proper orthogonal decomposition [22,23,24,25,26], and in this paper we apply this technique to experimental data obtained by Kratěna et al [16,17,18] by measuring the tangential component of the force exerted on radial baffles by the liquid flow in a mixing vessel in order to quantify the relative magnitude of its macro-instability related component, to analyse its vertical distribution in the vessel and the effects of the frequency of the impeller revolution, the number of impeller blades and the liquid viscosity

  • The vertical distribution of the magnitude and the variability of the dimensionless tangential force affecting the baffle in the mixing vessel was analysed

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Summary

Introduction

Liquid flow in mechanically stirred vessels has been studied intensively on recent decades. The technique is based on a combination of spectral analysis with proper orthogonal decomposition [22,23,24,25,26], and in this paper we apply this technique to experimental data obtained by Kratěna et al [16,17,18] by measuring the tangential component of the force exerted on radial baffles by the liquid flow in a mixing vessel in order to quantify the relative magnitude of its macro-instability related component, to analyse its vertical distribution in the vessel and the effects of the frequency of the impeller revolution, the number of impeller blades and the liquid viscosity. The frequency of occurrence of macro-instability related force component is analysed

Experimental
Numerical analysis of experimental data
Results and Discussion
Conclusions
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