Impeller high efficiency

Figure 7-15 shows plots of Pumping number Nq and Power number Np as functions of Reynolds number Np for a pitched-blade turbine and high-efficiency impeller. Hicks et al. [8] further introduced the scale of agitation, S, as a measure for determining agitation intensity in pitched-blade impellers. The scale of agitation is based on a characteristic velocity, v, defined by... 

Figure 7-15. Power number and Pumping number as functions of Reynolds number for a pitched-blade turbine and high-efficiency impeller. (Source Bakker, A., and Gates L. , Properly Choose Mechanical Agitators for Viscous Liquids," Chem. Eng. Prog., pp. 25-34, 1995.)...

Axial flow devices such as high-efficiency (HE) impellers and pitched blade turbines give better performance than conventional pitched blade turbines. They are best suited to provide the essential flow patterns in a tank that keep the solids suspended. High-efficiency impellers effectively convert mechanical energy to vertical flow... 

Maxflo T Wide-blade, high-efficiency impeller Blending, np and Nq varY with tjP an9le and Transitional flow, number of blades Simultaneous gas dispersion and solid suspension (like mining),... 

Recently, Corpstein et al. [43] found that high-efficiency impellers provide the same levels of solids suspension at reduced capital and operating costs. They introduced the term just-suspended for the most commonly encountered level of liquid solid agitation. This occurs when none of the solid particles remains stationary on the bottom of the vessel for longer than 1-2 sec. They developed a correlation of the speed required to achieve just-suspended conditions as ... 

The mixing of two nonreacting species in a tank equipped with a high-efficiency impeller (Chemineer HE-3) was calculated using Fluent... 

High-efficiency impellers such as HE-3 s and 4BP impeller are sometimes mounted above a 6BD or a CD-6. For these impellers, the effect of gassing on the power requirement is given in Bakker et al. (1994). 

K.J. Myers, R.R. Corpstein, A. Bakker, and J. S. Fasano, Solids suspension agitator design with pitched blade and high efficiency impellers, AIChE Symp. Series, 90(299), 186-190, (1994). 

Typical values for the impeller clearance off the vessel bottom are 7/4 for hydrofoil impellers and 7/3 for pitched-blade turbines. Hydrofoil impellers may be a poor choice when solid suspension is accompanied by other mixing duties, such as liquid-liquid dispersion or gas dispersion. For such cases, a multiple impeller system consisting of a high-efficiency impeller in combination with a 45"" pitched-blade impeller should be evaluated. Small pitched blade impellers with a... 

When the power number of the impellers is taken into account, it becomes clear that axial-fiow impellers (e.g., Lightnin A-310, Chemineer HE-3) are able to achieve the just-suspended state at a lower power input than other impellers, such as pitched-blade or disk turbines. The resulting axial fiow developed by high-efficiency impellers is higher at the vessel base, per unit of power expended, than that for radial fiow impellers. These impellers are also more effective at higher clearances from the vessel base, i.e., larger C/T values. 

FIG. 14.5 (a) Pitch blade impeller, (b) high-efficiency impeller, (c) straight blade turbine... 

The fluidfoil impellers are often called high efficiency impellers , but that is true only in terms of flow, and makes the assumption that flow is the main measure of mixing results. Flow is one measure, and in at least half of the mixing applications is a good measure of the performance fliat could be expected in aprocess. These impellers are low in efficiency in providing shear rates—either of the macro scale or the micro scale. 

Figure 5-38 Flow pattern at the surface of a vessel equipped with a high efficiency impeller calculated using an LES turbulence model.

SOLUTION (a) For this simple dissolution a high efficiency impeller will be used (see below for the rationale). From Table 10-3 select an A-310 impeller with diameter, D, equal to the half the vessel diameter, T (i.e., D = T/2, 24 in. or 0.61 m and located at T/4 from the vessel bottom). First, calculate Njs using the Zwietering correlation. 

Haam, S. J., R. S. Brodkey, and J. B. Fasano (1993). Local heat transfer in a mixing vessel using a high-efficiency impeller, Ind. Eng. Chem. Res., 32, 575-576. 

Condition High Efficiency Impeller 45 Pitched Four-Blade ImpellCT... 

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