Search results for "Stirred tank"

Mixing dynamics in uncovered unbaffled stirred tanks

2014

Abstract The present work is aimed at providing experimental information on mixing rates in an unbaffled vessel under free surface vortexing conditions. The planar laser induced fluorescence (PLIF) technique was used for measuring the dispersion dynamics of a passive tracer over a vertical section of the vessel. In agreement with the quite scant literature information available for these systems, results confirm the existence of two well defined, partially segregated, zones that give rise to a double mixing dynamics behavior. A suitable mixing time definition is proposed and applied to a number of experimental runs with different stirrer geometries and agitation speeds. Results confirm that…

Suspension phenomena in solid-liquid agitated systems

2011

Turbulent Fluid Flow in Closed- and Free-Surface Unbaffled Tanks Stirred by Radial Impellers

1996

SIMULAZIONI CFD DEL CAMPO DI MOTO A BASSO NUMERO DI REYNOLDS IN BIOREATTORI AGITATI CON E SENZA SETTI FRANGIVORTICE

2016

I recipienti meccanicamente agitati sono apparecchiature frequenti dell’industria chimica di processo. Questi sono tipicamente dotati di setti frangivortice (recipienti baffled) atti a rompere il moto prettamente tangenziale tipico dei recipienti sprovvisti di setti (recipienti unbaffled) e convertirlo in moto assiale e radiale. La presenza dei setti evita inoltre nella zona centrale del sistema la formazione del vortice d’aria che può talvolta essere indesiderato o in taluni casi creare instabilità una volta arrivato alla girante. I recipienti unbaffled sono considerati quindi dei miscelatori meno efficienti rispetto a quelli provvisti di setti. Tali sistemi sono pertanto ad oggi impiegati…

On vortex shape in unbaffled stirred vessels as measured by digital image analysis

2012

In this work, digital image analysis coupled with a suitable shadowgraphy-based technique is employed to investigate the shape of the free-surface vortex that forms in uncovered unbaffled tanks stirred by either a D=T/3 Lightnin A310 or a D=T/3 Rushton turbine. The technique is based on back-lighting the vessel and suitably averaging vortex images over time. Data obtained show that the two different impellers give rise to quite different vortex shapes. A novel 2-parameter model is proposed that successfully describes vortex shapes obtained with both impellers.

Particle distribution in dilute solid liquid unbaffled tanks via a novel laser sheet and image analysis based technique

2013

The availability of experimental information on particle distribution inside stirred tanks is a topic of great importance for many industrial applications such as catalysis and polymerization. The measurement of solid particle distribution is not simple and the development of suitable measuring techniques is still an open problem in chemical engineering research. In this work, a non-intrusive optical technique for measuring particle concentration fields in solid–liquid systems is discussed. The “Laser Sheet Image Analysis” (LSIA) technique described here makes use of a laser sheet, a digital camera for image acquisition and a suitable procedure for post-processing. It is able to provide sol…

CFD MODELLING OF PARTICLE SUSPENSION IN STIRRED TANKS

2011

Mixing of solid particles into liquids in mechanically agitated vessels is a topic of primary importance for several industrial applications. A great deal of research efforts has been devoted so far to the assessment of the minimum impeller speed (Njs) able to guarantee that all particles are suspended. Conversely, only little attention has been paid to the evaluation of the amount of solid particles that are suspended at impeller speeds N lower than Njs, despite the fact that in a number of industrial applications agitation speeds smaller than Njs are actually adopted [1,2]. The present work deals with dense solid-liquid partial suspensions in baffled stirred tanks and particularly focuses…

Measurements of Njs and Power Requirements in Unbaffled Bioslurry Reactors

2012

The remediation of urban/industrial polluted lands is a topic of crucial importance nowadays. Bioremediation techniques are widely employed to remove organic pollutants from contaminated soils because of their simplicity and cheapness. The bioslurry reactors mechanically agitated by stirrers represent one of the most promising bioremediation techniques. In the present work an unbaffled stirred vessel filled with solids and water is experimentally investigated from a fluid dynamic point of view. Air presence within the tank is guaranteed by the central vortex formation (typical occurrence concerning stirred vessels unprovided with baffles) instead of an intrinsically more expensive insufflat…

Power requirements for complete suspension and aeration in an unbaffled bioslurry reactor

2016

Remediation of contaminated soils is spreading as a matter of crucial importance nowadays. Bioremediation via bioslurry reactors of sites polluted by recalcitrant pollutants has been proved to be a valuable option, although optimization is needed to reduce process costs. Free-surface unbaffled stirred tanks (with central air vortex) have been recently proposed as a promising alternative to the more common systems provided with baffles. In a bioslurry reactor solid-liquid interfacial area, oxygen supply, solid loading per reactor unit volume should be maximized, and, at the same time, operation costs have to be kept low. In this regard, the minimum impeller speeds for complete suspension Njs…

Particle Suspension in Vortexing Unbaffled Stirred Tanks

2016

Three-phase processes in which particle suspension has to be achieved in conjunction with gas dispersion are traditionally carried out in sparged, baffled stirred tanks. The operation of such tanks can suffer, however, from particles tending to block the sparger holes. A viable alternative might be provided by uncovered unbaffled stirred tanks (UUSTs), where gas self-injection can occur when the free-surface vortex reaches the impeller blades and gas bubbles begin to be ingested by the liquid. In this work, the particle suspension and liquid aeration performances in three-phase UUSTs were experimentally investigated and compared with relevant literature correlations concerning baffled syste…