Helical Mixers

M 81] [P 70] A plot of the normalized intensity versus the down-channel length clearly shows that the mixing efficiencies of the devices have the following sequence barrier-embedded helical mixer > helical mixer pipe mixer (see also Figure 1.165) [3]. The relative degree of mixing performance is lower for the pipe mixer than for the other two helical mixers. This is most evident for the three plots with Re > 13.96. 

There are several types of mixers helical ribbon, ribbon bar or paddle mixers. 

The mixer helical elements were of polypropylene construction Le/D = 0.833. 

Helical Ribbon Mixers Helical ribbon mixers (Fig. 18-44), or simply helix mixers, have major advantages over the anchor mixer, because they force strong top-to-bottom motion even with viscous... 

With mechanically agitated countercurrent extractors, energy is induced by rotating internals. Agitators are usually mounted on a central column shaft at certain distances from each other (double blade mixer, disc mixer, blade mixer, turbine mixer, helical screw mixers, etc.). Installation of stators (ring discs, punched metal sheets. 

Top entering mixers are heavy duty equipment. They are usually fixed to a rigid structure or tank mounting. Either radial flow or axial flow turbines may be used. Speeds vary from 50 to 100 rpm and usually require a double set of helical gearing or a single set of worm gears to achieve these low speeds. Therefore, they are more expensive than single reduction mixers. 

The Kenics STATIC MIXER unit is a series of fixed, helical elements enclosed within a tubular housing. The fixed geometric design of the unit produces the following unique patterns of flow division and radial mixing simultaneously. 

Madison, Application of Large Vertical Helical Mixer for Mixing Composite Propellants , Paper AlChE 60th Meeting, Atlantic City, NJ... 

One of the benefits of static mixers like those mentioned above are the secondary flow patterns set up by the swirling helical flow. 

Entrop (17) reported the process characteristics of the Nauta mixer. The Nauta mixer utilizes the orbiting action of a helical screw, rotating on its own axis, to carry material upward, while revolving about the centerline of the cone-shaped housing near the wall for top-to-bottom circulation, (see the sketch in Fig. 16). Nauta mixers of different sizes are not built geometrically similar to each other, but the diameter of the helical screw and its pitch are kept equal. 

The measurements were executed under the the following conditions mixer volume F= 0.05-10 m diameter of the helical screw [Pg.39]

From the enery point of view, it is therefore advantageous to construct mixers of low heights and to provide them with helical screws of large diameters. 

The Kenics mixer, Figure 10.14(a), for example, consists of a succession of helical elements twisted alternately in opposite directions. In laminar flow for instance, the flow is split in two at each element so that after n elements the number of striations becomes 2". The effect of this geometrical progression is illustrated in Figure 10.14(b) and points out how effective the mixing becomes after only a few elements. The Reynolds number in a corresponding empty pipe is the major discriminant for the size of mixer, one manufacturer s recommendations being... 

Figure 10.14. Some kinds of in-line mixers and blenders, (a) Mixing and blending with a recirculating pump, (b) Injector mixer with a helical baffle, (c) Several perforated plates (orifices) supported on a rod. (d) Several perforated plates flanged in. (e) Hellical mixing elements with alternating directions (Kenics Corp.). (f) Showing progressive striations of the flow channels with Kenics mixing elements.

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