Baffles curved

Froude number is of importance if vortexing occurs, as in an unbaffled vessel (curve BE), but of no importance if the vessel is fully baffled (curve CD). The detailed curves for various circumstances are given elsewhere (R6), and the influence of such variables as d/T, d/Z, number of blades on the turbines, etc., can reasonably well be estimated. 

Fig. 22. Mixing-time characteristics of the stirrer types in Fig. 21 (curve h for 21h without baffles curve hs for 21h with baffles, etc.). (Reprinted with permission from the publisher, VCH Publishers, Inc., after Zlokarnik and Judat, 1988.)...

For counterflow plates, the curves of Fig. 14-25 may be used for open areas of 20 percent or greater. Plates with 15 percent open areas have about 85 percent of the cui ve values, and open areas or less than 15 percent are not recommended. For counterflow-plate columns of the segmental-baffle type, 50 percent cut, allowable values are about 15 percent greater than tnose shown in Fig. 14-25, when vertical spacings of the baffles are equal to the trav spacings shown. 

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. 

Curves a to e are for open vessels, witb a gas-hquid surface, fitted witb four baffles, h = d,/10 to d,/12. 

Curve g is for disk flat-blade turbines operated in unbaffled vessels filled witb liquid, covered, so tbat no vortex forms. If baffles are present, tbe power characteristics at high Reynolds numbers are essentially tbe same as curve h for baffled open vessels, witb only a slight increase in power. 

The distribution of velocity components (radial, tangential and axial) under conditions of mixing with baffles in comparison with the conditions of vortex formation is presented in Figure 12. The dashed lines in Figure 12 indicate non-baffled conditions. Comparison of the non-baffled and fully baffled velocity curves (solid line) leads to the following set of conclusions on vortex suppression when dealing with perfectly miscible liquids ... 

Figure 5-5G. Curved-blade turbine, devei-oped especlaily for agitating fibrous materials such as paper stock. Also used on oil well drilling muds. This impeller gives fast, thorough turnover without need for the usual tank baffling or mid-feather construction. Courtesy of Lightnin (formerly Mixing Equipment Co.), a unit of General Signal.

Figure 10-54. Shell-side heat transfer curve for segmental baffles. (Used by permission Engineering Data Book Section II, 1959. Wolverine Tube, Inc.)...

For longer units requiring support plates for the tubes, the pressure drop will still be very small or negligible and can be estimated by Figure 10-140 using the appropriate baffle cut curve to match the tube support cut-out of about 50%. Kem recommends that the flow be considered similar to an annulus of a double pipe and treated accordingly. 

Mixing concepts, fundamentals, 297 Actual motor horsepower, 307 Axial flow, 291 Baffle diagrams, 318 Baffles, 311 Calculations, 297 Characteristic curves, 306 Draft lubes, 309, 312, 313 Entrainment, 309 Flow number, 298 Flow patterns, 309-313 Flow, 298... 

Power curves for many different impeller geometries, baffle arrangements, and so on are to be found in the literature/10111719 2I but it must always be remembered that though the power curve is applicable to any single phase Newtonian liquid, at any impeller speed, the curve will be valid for only one system geometry. 

Figure 5.9 Design of a generalized microbial cell fermentation vessel (a) and an animal cell bioreactor (b). Animal cell bioreactors display several structural differences compared with microbial fermentation vessels. Note in particular (i) the use of a marine-type impeller (some animal cell bioreactors-air lift fermenters-are devoid of impellers and use sparging of air-gas as the only means of media agitation) (ii) the absence of baffles (iii) curved internal surfaces at the bioreactor base. These modifications aim to minimize damage to the fragile animal cells during culture. Note that various additional bioreactor configurations are also commercially available. Reprinted with permission from Proteins Biochemistry and Biotechnology (2002), J. Wiley Sons...

Figure 5.8 shows the power curve for the standard tank configuration geometrically illustrated in Figure 5.5. Since this is a baffled non-vortexing system, equation 5.20 applies.

The power curve in Figure 5.8 for the baffled system is identical with the power curve in Figure 5.9 for the unbaffled system up to point C where ReM = 300. As the Reynolds number for mixing ReM increases beyond point C in the unbaffled system, vortexing increases and the power falls sharply. 

Power curve for the standard tank configuration without baffles... 

The values of VP are approximate. At low Reynolds numbers, about 300, the power number curves for baffled and unbaffled tanks are identical (McCabe et al., 1993). For higher NAV, the power number for unbaffled tanks is lower than the values for baffled tanks. 

A large number of impeller types have been studied over the years, but interest has centered on three designs marine-type propellers, flat-or curve-bladed turbines, and flat paddles, with the first two of greater interest than the third. Propellers produce axial flow of the liquids and are turned in such fashion as to direct flow against the bottom of the tank. Turbines provide radial flow, but in any case the presence of baffles strongly influences the flow pattern in the tank. The effectiveness of these in liquid extraction has not been well established, but it appears that there... 

The Reynolds number NBe accounts for viscous forces, and the Froude number NFr for the force of gravity when this is important. For a typical impeller-tank arrangement, curves of the sort shown in Fig. 1 result, based on Eq. (2). Briefly, at low values of NRe (viscous flow, A to 5 in the figure) for both baffled and unbaffled tanks, no vortex is produced and the Froude number is unimportant n = 0). In turbulent flow the... 

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