Smith impeller

The recently developed hoUow-blade impellers (e.g., Scaba SRGT, Chemineer CD6, and the Smith impeller) provide better gas dispersion and higher gas-holding... 

The time required to pass through the high shear zone will be proportional to the volume of the vessel divided by the flow from the turbine. This will be porportional to 1/ND. With a turbine in turbulent flow, turnover is relatively rapid and all the fluid will pass through the impeller region in a relatively short period of time. The flow regime in an anchor or helically agitated vessel can be inferred from the flow studies by Smith and Peters (], 13j. These indicated... 

Jiisten [60] took the quantity P/(Vj tp) Zp P/Vj for the correlation of his results which means that in larger reactors less stress takes place at the same power input P/Vj. The assumption that the number of circulations through the impeller zone Zp is decisive for the load of organisms was put forward by Smith, Lilly, Fox [74]. This parameter cannot be important since the circulation frequency l/tp Zp is normally small in comparison to the frequency of turbulent... 

The observed values of the mass transfer coefficient- in three-phase systems between solid and liquid for the conventional impellers and a typical baffled vessel (e.g. Rushton turbine, propeller) are between the values predicted by Hiraoka (liquid-liquid dispersion, eq. (3.267)) and Levins and Glastonbuty (solid-liquid dispersion, eq. (3.118)) correlations. However, as an approximation, the Levins and Glastonbuty correlation could be used for three-phase systems (Smith, 1981). 

Flooding of Agitator Impellers Impeller flooding correlations for six-blade disk (6BD) Rusthon turbines and six-blade disk Smith turbines (Chemineer designation CD-6) are presented by Bakker, Myers, and Smith [Chem. Eng., 101, 98 (Dec. 1994)] and a review of impeller flooding. The Bakker et al. (loc. cit.) correlation is... 

A new impeller is now being used for gas-liquid contacting, call the Smith Turbine. It is a radial flow turbine with blades as shown in Fig. 25. It is rotated in the concave... 

FIGURE 4.8 Pump characteristic curves for a 375-mm impeller. (Courtesy of Smith and Loveless. With permission.)... 

Bakker, Smith, and Myers combined the results of Nienow and those of Warmoeskerken and Smith to establish an equation for the determination of the transition point at which the gas becomes completely dispersed in the liquid (in the regions both below and above the impeller). For flat-blade disk turbines, the expression that they found... 

Correlations have also been developed for Pq. Bakker, Smith, and Myers report the following equation for a single gassed impeller ... 

Smith, J.M. Gao, Z. Muller Steinhagen, H. Void fraction distributions in sparged and boiling reactors with modem impeller configurations. Chem. Eng. Process. 2001, 40, 489-497. 

Smith, J.M. Warmoeskerken, M.M.C.G. Zeef, E. Flow conditions in vessels dispersing gases in liquids with multiple impellers. In Biotechnology Processes, Ho, C.S., Oldshue, J.Y., Eds. AIChE... 

Smith et al (1968) looked at mass transfer of a batch dialyser of similar geometry to those of the stirred cells. In summary, mass transfer reduced as stirrer diameter reduced. Mass transfer is lowest at the centre of the impeller. The transition between laminar and turbulent regimes occurred between Re of 20 000 and 30 000. The closer the impeller to the surface, the higher the mass transfer. 

The flow in an anchor agitated vessel has been studied in detail by Peters and Smith . The impeller promotes fluid motion close to the vessel wall but the region near the shaft may be relatively stagnant. In addition, there is little top-to-bottom turnover. In order to promote a top-to-bottom motion a helical ribbon may be used and often a screw is added to the shaft to obtain motion in the central regions of the vessel. This combined impeller system would have a ribbon pumping upward near the wall of the vesel with the screw, twisted in the opposite sense, pumping downwards near the shaft. 

It is not yet established, however, how strongly the value of kg depends on the rheology, and on the geometrical arrangement of the system. For example, both Calderbank and Moo-Yoimg [1959] and Beckner and Smith [1966] have related ks to the impeller/vessel configuration and the power-law index, n the dependence on, n, however is quite weak. 

The flow patterns for single phase Newtonian and non-Newtonian fluids in tanks agitated by class 1 impellers have been reported in the literature by, amongst others, Metzner and Taylor [1960], Norwood and Metzner [1960], Godleski and Smith [1962] and Wichterle and Wein [1981]. The experimental methods used have included the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles and measurement of local velocities by... 

Figure 8.11 Shear rate profiles for an anchor impeller rotating in a visco-elastic liquid [Peters and Smith, 1967]...

While anchors and gate-type impellers are known to produce poor axial circulation of the liquid in a vessel, in one study [Peters and Smith, 1967] it seems that the fluid visco-elasticity promotes axial flow. For instance, axial flow is reported to be almost 15 times greater in a visco-elastic solution as compared with a Newtonian medium. The shear rate profiles reported by these authors shown in Figure 8.11 clearly indicate that the liquid in the tank is virtually unaffected by the blade passage. 

In addition to the primary flow pattern referred to above, secondary flow cells develop with increasing impeller speed and these are similar to those observed by Peters and Smith [1967] for class 11 agitators as can be seen in Figure 8.13. Carreau et al. [1976] have also recorded flow patterns for a helical ribbon impeller. sco-elasticity seems to cause a considerable reduction in the... 

The only study relating to the use of class II impellers for non-Newtonian media is that of Peters and Smith [1967] who reported a reduction in mixing and circulation times for visco-elastic polymer solutions agitated by an anchor... 

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