Air Water

Figure 26. Typical curve of K factor, power drawn with gas on versus power drawn with gas off, for various superficial gas velocities.
Standard Height For Geyser Placed
Figure 27. Schematic of geyser height.

GEYSER HEIGHT, INCHES

Figure 28. Plot illustrating measurement of geyser height.

GEYSER HEIGHT, INCHES

Figure 28. Plot illustrating measurement of geyser height.

Also, the 8-inch impeller with standard blades was more effective than the 8-inch impeller with narrow blades. These results all indicate that in this range of impeller-size-to-tank-size ratio, pumping capacity is more important than fluid shear rate for this particular criterion of physical dispersion.

Looking now at some actual published mass transfer rates, Fig. 29 shows the results of some experiments reported previously and Figs. 30 through 33 show some additional experiments reported which give further clarification to Fig. 29.

In Fig. 29, the ratio of mixer horsepower to gas expansion horsepower is shown with the optimum D/T range from a mass transfer standpoint in air-water systems. At the left of Fig. 29, it can be seen that large D/T ratios are more effective than small D/T ratios. This is in an area where the mixer power level is equal to or perhaps less than the gas expansion power level. Moving to the right, in the center range it is seen that the optimum D/T ratios are on the order of 0.1 to 0.2. This corresponds to an area where the mixer power level is two to ten times higher than the expansion power in the gas stream. Thus shear rate is more important than pumping capacity in this range, which is a very practical range for many types of gas-liquid contacting operations, including aerobic mass transfer in fermentation.

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