Variable depth mixers

In variable depth mixers, the channel depth of the mixer is varied to obtain improved mixing. An example of a variable depth mixer is the double wave screw shown in Fig. 8.81 and the energy transfer screw see Fig. 12.23. Another example is the Pulsar mixing section shown in Fig. 8.103. 

In the Pulsar mixer a helical groove is machined into the root of the screw the helix angle of the groove is greater than the helix angle of the flight. As a result, some 

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The channel depth varies periodically in each channel in such a way that when one channel decreases in depth, the other increases and vice versa. In this mixer there is no strong mechanism for flow splitting and reorientation. Thus, the mixing capability of this mixer is moderate. Other variable depth mixers are the Pulsar and Strata-blend mixing sections (see Fig. 57). These do not achieve efficient flow splitting and reorientation. 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

Splitting and reorientation is critical to achieving efficient distributive mixing, because mixing can improve exponentially by splitting and reorientation. Distributive mixers can be divided into some main groups cavity mixers, pin mixers, slotted flight mixers, variable channel depth mixers, and variable channel width mixers. 

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