Gas–liquid dispersion with dual Rushton impellers

Abstract

Aerated and unaerated power consumption and flow patterns in a 0.56 m diameter agitated vessel containing water with dual Rushton turbines have been studied. Under unaerated conditions with a liquid height-to-diameter ratio of 2, an impeller spacing of 2 to 3 times the impeller is required for each to draw an amount of power equal to a single impeller. For aerated conditions, if a similar spacing is used, equations for the flooding-loading transition and for power consumption for a single Rushton impeller can be extended relatively easily to dual systems. All results for this spacing are explained by reference to bulk flow patterns and gassed-filled cavity structures and the proportion of sparged gas flowing through the upper impeller is also estimated. Such a spacing is generally recommended since it maximizes the power draw and hence the potential for oxygen mass transfer. Data are presented for other spacings but the results do not fit in easily with single agitator studies because strong impeller-impeller flow pattern interactions occur.

Flow Induced by Dual-Turbine of Different Diameters in a Gas-Liquid Agitation System: the Agitation and Turbulence Indices

“…The two characteristic ring vortices of this kind of systems are observed here. However, the results obtained differ from that reported in Kuboi & Nienow (1982) and Hudcova et al (1989), where the impeller streams follow an almost straight-line orientation toward one another until they merge at an elevation approximately midway between the impellers. In this agitation system the stream from the lower impeller is not observed and the upper ring vortices of both impellers seem to be fused, forming one vortex with the centre in the midway between the impellers.…”

“…The gas -liquid dispersion process in stirred tanks with standard geometry, equipped with a ring sparger and dual-turbine agitation system, where the liquid height is larger than the tank diameter (H > T) has been widely reported (Abrardi, et al, 1988;Hudcova, et al, 1989;Roman & Gavrilescu, 1994;Vasconcelos et al, 1998). However, in the literature is scare the experimental data concerning aeration-agitation system with all the following characteristics: a) H = T (Kuboi & Nienow, 1982), b) baffles fixed away from the wall and the bottom, c) tanks with curved bottom (Bouaifi & Roustan, 1998), and d) dual-turbine impellers.…”

Laser Doppler Measurements of Turbulent Parameters in Different Multiple-Propeller Systems

“…If the Taylor hypothesis is fulfilled, the dissipation rate of kinetic energy e, the Taylor length microscale l s , and the Kolmogorov microscale h can be calculated from the frequency spectrum [20] with relations (3), (4), and (5).…”

“…In this case, the lower impeller produce only one circulation loop. Changes in flow pattern are linked to variations of power consumption [4,5] and mixing time [6]. The association of two pitched blades turbines has been recently studied by Mishra et al [7].…”

Effect of Dual Impeller‐Sparger Geometry on the Hydrodynamics and Mass Transfer in Stirred Vessels

“…The influence of clearance between the impellers on the hydrodynamics in different aerated-agitated standard systems has been studied by several authors [6,12]. Surprisingly, agitation systems with dual turbine impellers of different diameters have rarely been considered for gas dispersion.…”