Special Mixers

Foaming with air is obtained in special mixers such as the Oakes mixer and the expansion takes place during gelation in hot air or a high-frequency oven. 

Reactions completed within the dead time of stopped-flow instruments cannot be measured dead times are on the order of milliseconds for conventional instruments but can be somewhat shorter if special mixers are used. 

In another US patent, [47], polyolefins and tires scrapes mixture is fed to the batch reactor equipped with a special mixer. A screw extruder or other device is used for feed... 

For the semi-dry process, dry starch is fluidised in a special mixer to which are added the various reagents in dilute form. Water needs to be present to carry the chemicals into the starch granule. The process is continuous with the product being dried in line, sieved and bagged. 

This raises the question of whether water could be recirculated. One makes a distinction between outer and inner water recirculation. In the former, water vapor coming out of the anode compartments (and consisting of the two components water as a reaction product and evaporated solution water) is condensed and redirected into a special mixer. In this mixer, pure methanol is admixed, as needed for maintam-ing the required solution concentration, while the reaction proceeds. The methanol concentration can be controlled with different sensors. 

Simplicity, mixing time can be controlled (with special mixers), possibility to incorporate multiple mixers... 

It is advisable to perform the sampling as a weight-dependent rather than as a time-dependent operation. In the former case the sampler is controlled direct by a belt weigher. The cumulative sample is homogenized in a special mixer after a certain quantity (tonnage) of material has been collected. With both methods suitable belt conveyors and automatic counting equipment are required. The samplers can be adjusted to take any desired quantity. 

The number of cells in a flotation circuit is determined by the degree of metalluigical control and the concern for short-circuiting. It used to be believed that the correct approach would consist of small cells and longer banks. However, with the advent of special mixers and good aeration techniques, it is now possible to use larger tanks (Figure 7-29). 

Plastication by kneading is done in variable shear roll mixers, in rotor mixers of the Banbury or Wemer-Pfleiderer type, or in twin-screw extruders or in special mixers. Plastication made in two-roll mixers is not economical and it is used mainly for batch production or to mix substances of different natures. For continuous line production, single or twin-screw extruders or a Buss KO-Kneader are used. These mixers or extruders operate in a friction mode this friction is obtained by a horizontal backward and forward motion of the screw. The screw may have threads or flights of regular width or of lai ger width and slantly cut in the rotational direction (see Fig. 14.10). Homogenization in these machines is so efficient that even fish-eyes present in PE and suspension polymerized PVC can be disaggregated [8]. 

Except for some portable mixers, high-shear mixers, and a few special mixers, most mixers operate below standard motor speeds. Typical motor speeds of 1800 or 1200 rpm (30 or 20 rps) are reduced to between 350 and 30 rpm (5.8 and 0.5 rps) for most mixer applications. Portable and side-entering mixers usually operate near the upper portion of this speed range from 420 to 170 rpm (7 to 2.8 rps). Turbine mixers operate in the middle range, from 125 to 37 rpm (2.1 to 0.6 rps), and high viscosity mixers operate from 45 to 20 rpm (0.75 to 0.33 rps) and slower. 

The novel polymer slurry drag reduction method used by Little et al. [2] has been recently researched by Mamonov et al. [25]. Mamonov et al. [25] were able to prepare poly(ethylene oxide) solutions in less than 2 seconds using a special mixer and injected into the flow in a non-fu ly dissolved state. The reported results indicate that more drag reduction occurs when quickly prepared solutions have more time to dissolve. However, no data were reported for drag reduction effects with respect to time,... 

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