The distribution of buoyant solids in agitated suspensions has been studied. The investigation was carried out in a baffled vessel characterised by an aspect ratio equal to four and stirred with four radial impellers. Dilute suspensions of single-sized spherical particles of expanded polystyrene (density equal to 90.7 kg/m3) in water were used. Solid concentration was measured with a non-intrusive optical technique. Measurements were performed along the axis of the reactor to obtain steady-state vertical profiles as well as at fixed elevations to determine the concentration transient after a pulse of solids injected at the bottom. Both the transient concentration curves and the steady-state profiles were interpreted by means of the axial dispersion model with sedimentation. The particle rising velocity in the agitated system was determined by data treatment; it proved to be significantly smaller than the free-rising velocity, i.e. the rising velocity in a still liquid. The ratio of these two velocities is in reasonable agreement with a correlation of the ratio of the settling velocities of heavy particles with the ratio of the Kolmogorov microscale to particle diameter established previously.

Solids distribution and rising velocity of buoyant solid particles in a tank stirred with multiple turbines: a simplified approach for the study of sparged gas-liquid reactors (Paper 7.4)

PINELLI, DAVIDE;FAJNER, DANIELE;MONTANTE, GIUSEPPINA MARIA ROSA;PAGLIANTI, ALESSANDRO;MAGELLI, FRANCO
2008

Abstract

The distribution of buoyant solids in agitated suspensions has been studied. The investigation was carried out in a baffled vessel characterised by an aspect ratio equal to four and stirred with four radial impellers. Dilute suspensions of single-sized spherical particles of expanded polystyrene (density equal to 90.7 kg/m3) in water were used. Solid concentration was measured with a non-intrusive optical technique. Measurements were performed along the axis of the reactor to obtain steady-state vertical profiles as well as at fixed elevations to determine the concentration transient after a pulse of solids injected at the bottom. Both the transient concentration curves and the steady-state profiles were interpreted by means of the axial dispersion model with sedimentation. The particle rising velocity in the agitated system was determined by data treatment; it proved to be significantly smaller than the free-rising velocity, i.e. the rising velocity in a still liquid. The ratio of these two velocities is in reasonable agreement with a correlation of the ratio of the settling velocities of heavy particles with the ratio of the Kolmogorov microscale to particle diameter established previously.
Proc. ISMIP VI
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R.S. Ghadge; D. Pinelli; D. Fajner; G. Montante; A. Paglianti; F. Magelli
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/63704
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