Tube stirrer —» Hollow stirrers

Figure 11. Electrodes in microcalorimetric vessels. A Schematic diagram of a section through a titration-perfusion microcalorimetric vessel equipped with a polarographic oxygen electrode and a pH electrode, a, sample compartment, volume 3 ml b, hollow stirrer shaft c, steel tube d, turbine stirrer e, O-rings f, combination pH electrode protected by a steel tube g, polarographic oxygen sensor (Clark electrode). B Record from a growth experiment with T-lymphoma cells. The vessel was completely filled with medium. Once the baseline had been established, the experiment was started (as indicated by the arrow) by the injection of 100 pi concentrated cell suspension.

Fig. 6. Hollow stirrer (tube type). (Reprinted with permission from the publisher, VCH Publishers, Inc., after Zlokarnik and Judat, 1988.)...

The gas throughput characteristic of a hollow stirrer generally has the form /VA = /(Fr dy H, Ga, dr/dt, HJdf), where NA = qt/(Ndf) is the dimensionless flowrate number, Fr s Ndjg the Froude number, and Ga = dfg/v2 the Galileo number. For liquids with viscosities close to that of water and for HJd = 1, the gas throughput characteristics for the tube stirrer shown in Fig. 9 are as follows ... 

Nicholson, developed processes for the successful bulk production of nitrobenzene and aniline in batteries of closed iron reactors fitted with power-driven stirrers (Figure 6). For aniline, Nicholson adopted the B6champ reduction process and introduced steam into the reaction mixture by employing a hollow stirrer tube. The product aniline was obtained by distilling with steam after the addition of lime. Within a few years the standard reduction mixture became iron filings and hydrochloric acid. Production improvements and better quality benzene enabled aniline to be obtained in 90-95% yield. 

A gas-inducing agitator system is an alternative to a multistirrer system. It contains a hollow shaft with orifices above the liquid level and a hollow impeller. A typical hollow impeller consists of a tube that is, at the centre, connected to the hollow shaft. Both ends of the impeller are cut at 45 so that, at rotation, the open portions of the tube are at the near side of the stirrer. There are several modifications of this design. Obviously, there is a minimum impeller speed at which the onset of gas induction occurs. Loop reactors are also successfully used. 

The best material for a fusion apparatus (see Fig. 14a) in the laboratory is copper, which saves on gas because of its good conductivity and which is therefore economical in operation. (It is important that the melt does not come in contact with two diflFerent metals, because then a galvanic cell is formed which causes deleterious oxidation and reduction reactions.) The high fusion temperature makes it essential that the stirrer sweep over the whole surface of the fusion vessel (see sketch). The thermometer is inserted in a copper tube closed at the end with hard solder and filled with dry cylinder oil to such a depth that at least 10 cm. of the thermometer is immersed. It may be practical also to insert the thermometer in the hollow shaft of the stirrer (Fig. 14b). 

Due to the liquid circulation caused by the stirrer in the tank, helical coils should only be used with axially operating stirrers (propeller and pitched-blade stirrers), which are, on the other hand, not suitable for gas dispersion. Thus in bioreactors vertical heat exchange tube bundles are preferably used as baffles (see Fig. 1.3c). Occasionally, baffles are executed as hollow bodies, so that they can serve as heat exchangers. 

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