Agitators impellers

Flooding of Agitator Impellers A review of impeller flooding has been done by Sensei et al. [AlChE Symp. Series No. 283, 89 (1993)] and they have offered the following flooding correlation for a six-bladed disk-type turbine. 

FIG. 15-23 Power for agitation impellers immersed in single-phase liquids, baffled vessels with a gas-liquid surface [except curves (c) and (g)]. Curves correspond to (a) marine impellers, (h) flat-blade turbines, w = dj/5, (c) disk flat-blade turbines witb and without a gas-liquid surface, (d) curved-blade turbines, (e) pitcbed-blade turbines, (g) flat-blade turbines, no baffles, no gas-liquid interface, no vortex. 

Sg = specific gravity of fluid N = agitator impeller speed, rpm... 

For turbine agitators, impeller to tank diameter ratios of up to about 0.6 are used, with the depth of liquid equal to the tank diameter. Baffles are normally used, to improve the mixing and reduce problems from vortex formation. Anchor agitators are used with close clearance between the blades and vessel wall, anchor to tank diameter ratios of... 

The high shear stress around an agitation impeller is not acceptable for cell cultures or other sensitive materials in stirred (bio) reactors (Kato et. al., 2003 Michell et al., 1999). In these cases in which the solid phase is sensitive to high shear stress, shaking vessels can be used. The main types are the reciprocally and rotational shaking vessels. For these cases, see Kato et al. (2003). 

Figure 10.11. Power consumption, (a) Ratio of power consumptions of aerated and unaerated liquids. Q is the volumetric rate of the gas (O) glycol ( X ) ethanol ( ) water. [After Calderbank, Trans. Inst. Chem. Eng. 36, 443 (1958)]. (b) Ratio of power consumptions of aerated and unaerated liquids at low values otQ/Nd3. Six-bladed disk turbine ( ) water ( ) methanol (10%) (A) ethylene glycol (8%) (A) glycerol (40%) Pg = gassed power input P = ungassed power input Q = gas flow rate IV = agitator speed d = agitator-impeller diameter. [Luong and Volesky, AIChE J. 25, 893 (1979)].

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 conversion factor (see below) is used when working with English engineering units no factor is necessary for SI metric units. For a given impeller geometry, the power number is a constant for conditions of turbulent agitation. Values of turbulent power numbers for some agitator impellers are shown in Fig. 12.1. 

Determine impeller size for required power input. The impeller required for the process must draw 7.91 hp per 1000 gal or 79.1 hp for the 10,000-gal batch. This power level must be achieved at the gas flow rate required by the process, which is, Qa = 1507 ft3/min. The power required to operate an agitator impeller for gas dispersion can be much less than the power required for a liquid without gas. The ratio of power with gas to power without P/Po is shown in Fig. 12.7 and is a function of the dimensionless aeration number NAe =Qa/ND3. 

Agitation impellers act as caseless pumps. Measured pumping capacities for various impellers have been used to develop correlations of the flow number (Nq = Q/ND ), as a function of Nrj and system geometry. Figure 10.8 presents such a correlation for a 4BP and Figure 10.9 presents a pumping correlation for the HE-3. 

The choice of the optimum style of in-line mixer is not nearly as certain as is the choice of the optimum style of agitator impeller. However, a firm recommendation can be made based on the experimental record and on judgment. There are several considerations that lead to the recommendation of the Kenics helical element mixer (HEM) as the most suitable mixer for handling fast consecutive reactions ... 

The shaft work isolates that portion of the work which is deliberately done by a machine (e.g., pump impeller, fan blade, piston, agitation impeller, etc.) protruding through the control surface into the control volume. 

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