Stirrers cross-beam

The process characteristics of a cross-beam stirrer was established in this pi... 

Figure 9 Power characteristics for three slowly rotating stirrers (leaf, frame, cross-beam stirrers) installed in a vessel with and without baffles. Stirrer geometry and the installation conditions are given in Figure 10. (From Ref. 13.)...

In this pi-space, the process equation has been evaluated for the cross-beam stirrer, whereby the scale was altered by p = 1 2 and the process parameters were widely varied [15]. The process equation found reads... 

Cross-beam, grid and blade stirrers are slow-speed stirrers and are used at D/d = 1.5 to 2 both with and (in the case of viscous liquids) without baffles. They are particularly suitable for homogenization. 

The maximum stress on the baffles depended upon stirrer type. The following fmax/faverage values Were obtained 1.3 for cross-beam stirrer 1.6 for MIG 07 1.8 for turbine stirrer, and 2.5 for propeller stirrer. These values were independent of the tip speed of the stirrer. 

The proportionality constant fe depends upon the stirrer type. For propeller stirrers fe = 10 ]68], for turbine stirrers fe = 11.5 and pitched-blade stirrers fe = 13 [104]. For blade stirrers k = 2.5, for cross-beam stirrer fe = 4.1 and for helical ribbon stirrer fe = 6.0 [411]. Calderbank [66] found that when turbine stirrers were used with Bingham and pseudoplastic fluids fe = 10 and when used with dilatant liquids fe = 12.8 (d/D) 5. Lower fe values were found as the viscoelasticity of fluids increased [104]. In the case of close-clearance anchor stirrer fe depended upon the wall clearance [24]. 

This graphical representation enables an interesting comparison to be made between the power characteristics of different stirrer types. In the first place it is evident that the Ne value for Re = 1, i.e. NeRe = const) increases with the surface area of the stirrer, it being with the anchor stirrer a factor of 10 greater and with the helical ribbon stirrer a factor of 25 greater than that of the propeller stirrer. The smaller the wall clearance of the stirrer, the longer laminar flow conditions remain. With gate and cross-beam stirrers these are maintained up to Re 10, with anchor stirrers and helical ribbon stirrers even up to Re 10. ... 

Fig. 3.5 Mixing time characteristics of the stirrer types represented in Fig. 2.1 under given installation conditions from [611]. (The nD values for the cross-beam and the gate stirrer are by the factor given in the table higher than that of the blade stirrer, b - baffled tank)...

For cross-beam stirrers, whose beam number increases proportionally with H/D H/D= 1 4 beams H/D —2-. 9 beams H/D = 3 13 beams) the following relationship was found in the range H/D = 1 to 3 [611] ... 

Fig. 3.6 Mixing time characteristics for different H/D ratios the top graph holds for the cross-beam stirrer, the bottom for the propeller stirrer, after Fig. 2.1a and h, resp. from [611]... 

Results obtained with a cross-beam stirrer (see Fig. 2.1a and insert in Fig. 3.7) in tanks with D = 300 and 600 mm in the systems water/aqueous sugar syrup, glycerine solution or cooking salt solution and in which Apip and vi/v2 are varied over a considerable range, can be well described by the following relationship (see Fig. 3.7) ... 

Fig. 3.7 Mixing time characteristics for cross-beam stirrers at H/D = 1 in material systems with density and viscosity differences from [616]. 

P. Todtenhaupt [547] investigated the homogenization characteristic of a stirred column with 5 stirrers on the same shaft and flow from bottom to the top. Turbine, cross-beam, MIG and propeller stirrers were used. The stirred column was provided with round baffles, but did not possess partition trays between the individual stirred sections. Turbine stirrers performed the best and propeller stirrers conveying downwards the worst. For these two stirrer types the following process relationships apply ... 

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