Hydrofoil impeller

Hydroflusilicic acid Hydrofoil impeller Hydroformulation Hydroformylation... 

Fig. 9. Flow patterns with different impeller types, sizes, and liquid viscosity (a) FBT (b) hydrofoil (c) PBT (d) PBT, large diameter (e) PBT, high...

Fig. 12. Common impeller types (a) axial, (b) radial, (c) hydrofoil, and (d) closeclearance.

Derksen (2006a) continued along this line of approach and—by means of a clever strategy—mimicked the long-time behavior of solids suspension in an unbaffled tall stirred tank equipped with four hydrofoil impellers (Lightnin A310). The time span covered by his LES amounted to some 20,000 impeller revolutions (some 20 min). Running a LES for a Reynolds number of 1.6 x 10 over the entire time span is not an option, and for that reason a particular flow... 

Note The respective impellers used are a classical Rushton turbine (DT), a hydrofoil impeller (A315) manufactured by Lightnin, and a Pitched Blade impeller (PBT). The cases 1 through 4 all relate to a superficial gas rate of 3.6mm/s only, with impeller speeds varying between 5 and 10/s (gas flow numbers between 0.01 and 0.02) cases 2 and 3 differ in sparger size and position. 

Hydrofoil impellers, 16 673—674 Hydroformulation, 13 768 Hydroformylation, 10 598 allyl alcohol, 2 236—237 ionic liquids in, 26 882—885 maleic anhydride, 15 492 metal carbonyls in, 16 72—73 rhodium-catalyzed, 19 647 Hydroformylation reactions, 13 448 Hydrogasification, coal, 13 845 Hydrogel-based drug delivery,... 

Change impeller type with equal tip speed and adjusted torque per volume. Calculations similar to those of step 6 can be used to keep both tip speed and torque per volume constant when the impeller type is changed. Because volume does not change, that factor is removed from the calculations, but the change in impeller type means that power number must be included. In addition, a hydrofoil impeller is more efficient at creating liquid motion than a pitched-blade turbine therefore, the torque required by the hydrofoil impeller will be assumed to be half that of the pitched-blade turbine. The subscript 1 will be used for the pitched-blade turbine and the subscript 2 will be used for the hydrofoil impeller. 

Many types of multishaft mixers do not require planetary motion. Instead the mixers rely on an anchor-style impeller to move and shear material near the tank wall, while another mixer provides a different type of mixing. The second or third mixer shafts may have a pitched-blade turbine, hydrofoil impeller, high-shear blade, rotor-stator mixer, or other type of mixer. The combination of multiple impeller types adds to the flexibility of the total mixer. Many batch processes involve different types of mixing over a range of viscosities. Some mixer types provide the top-to-bottom motion that is missing from the anchor impeller alone. 

Fig. 2 Multiple impeller agitators down- and up-pumping hydrofoils above a radial dispersing impeller. (From Ref. l)...

Fig. 3 Various impellers (A) Rushton disk turbine, (B) hollow-blade turbine, (C) pitched-blade turbine, (D) narrow-blade hydrofoil (Lightnin A310), and (E) wide-blade hydrofoil (Lightnin A315). (From Ref. l)...

The value of g/u in Eq. (6) can easily fall as low as 0.4 for 6-blade flat-blade disk turbines (Fig. 6) and downflow pitched-blade turbines and hydrofoils (Table 3). However, for modern impellers with parabolic concave blades (e.g., Scaba SRGT, Chemineer BT6, Lightnin R-130), g/u typically falls to only about 0.9 (and then only at high FIq values). The ability to deliver high power makes these impellers highly suitable for gas-liquid operations. 

If higher power numbers are required, flat-blade turbines with more than six blades (preferably 12 or 16) can be used, for which Kq/o eventually drops to about 0.4, but not until much higher flow numbers than for six flat blades, g/u foi up-pumping wide-blade hydrofoils remains close to 1.0. Axial-flow impellers (e.g., Lightnin A345, Prochem Maxflo W, APV B6), if used for gas-liquid duty, should be preferentially operated in the upflow direction, when they are stable and maintain more than 70% of their ungassed power draw... 

Hari-Prajitno, H. Mishra, V.I. Takemaka, K. Bujalski, W. Nienow, A.W. McKemmie, J. Gas-liquid mixing studies with multiple up and down pumping hydrofoil impellers power characteristics and mixing times. Can. J. Chem. Eng. 1998, 76, 1056-1068. 

Recommended impeller diameter-to-tank diameter D/T) ratios, for liquid-liquid operations vary from 0.25 to 0.40 for radial disk turbines, from 0.4 to 0.6 for hydrofoils and propellers, and from 0.5 to 0.8 for retreat-curve, glassed-steel impellers. Vertical placement of the impeller depends on the vessel shape and the application. For dispersion by continuous addition of a dense phase fluid into a less dense fluid, the impeller should have a relatively small impeller clearance off the reactor bottom, C, with respect to the final height of the dispersion, H, i.e., the impeller should be placed low in the vessel (C H/A to H/S). For dispersion of light liquids, it is good practice to place a single impeller between 0.20 < C/H < 0.50. 

Multiple impellers are recommended it H/T 1.2 or if Ap > 0.15 kg/m. Assuming a less dense dispersed phase, the second or top impeller often is a hydrofoil impeller placed midway between the radial disk turbine and the surface of the liquid. This impeller produces high flow at low power, provides effective circulation, and complements the flow pattern produced... 

Use at least one axial flow hydrofoil-type impeller of high D/T (i.e., 0.4 < D/T < 0.6) in addition to the Rushton or RDT turbine for systems having large phase density differences. 

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