Static helical elements

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. 

The static elements were internals of a circular T-pipe. The mixer realized had Kenics cells with helical elements twisted by 180°, giving a fully 3-D structure (see Figure 1.163) [3], Two barriers were placed on the wall of the pipe. Counterclockwise-and clockwise-rotated helical elements were alternately arranged. Four barriers were introduced in the pipe wall in each Kenics cell. For comparison, pipes with only helical elements (no barriers) and empty pipes (no internals) were also fabricated. 

There are two kinds of static mixers. One type has helical elements that twist the fluid, and another set of elements that cut the fluid, divide it, and twist it again. The twisting and cutting is continued until the production and scaleup uniformity is achieved. This is useful in viscous fluids. 

Figure 10.48. Yield of the Dimethoxypropane Hydrolysis Reaction vs Static Mixer Residence Time for three Kenics Helical Element Mixer...

Fig. 5 Sequential lamination micromixer (II) (a) Static micromixer, with intersecting channel (top) and helical elements (bottom) (Reproduced from [91] by permission of The Royal Society of Chemistry), (b) Internal structure of crossing manifold micromixer (CMM) (Reproduced from [92] by permission of The Royal Society of Chemistry)...

Static mixers for viscosity ratio < 100 1 and Re > 10000, use turbulent vortex element for viscosity ratio > 100 1 and Re < 10000 use helical elements. For pipe diameter < 0.3 m, element is 1.5 X pipe diameter for pipe diameter > 0.3 m element = pipe diameter. For Re< 10 use 18 elements with the number of elements reducing to 2 as Reynolds no. increases to > 5000. 

A, Bertsch, et al. Laminar flow in static mixer with helical elements, 1998, http // www,bakker.org/cfmbook/lamstat,pdf... 

The mixing and flow patterns of gravitational dry particulate flows in continuous mixer tubes with helical, Kenics-type [1] static mixer elements have been simulated by the distinct element method (DEM) under steady state conditions. In the particular system the subsequent mixer elements were twisted in opposite direction a mixing element twisted clockwise is followed by an element twisted counter-clockwise and so on. A state diagram that gives a general relationship between the mass flow rate and the solids volume fraction in the mixer tube was determined for various construction parameters. 

The flow and mixing characteristics of dry particulate flows were studied in continuous mixer tubes with helical static mixer elements. In accordance with the visual observations and the actual experimental results, DEM simulation confirmed the presence of three different flow regimes. 

Mixing mixing of two component materials can be done using a static (sometimes called motionless ) mixer where the materials are forced through a series of right- and left-handed helical elements at 90° with no moving parts. Dynamic mixers that use... 

Two-part mixed-type acrylic adhesives are applied like two-part mixed epoxy adhesives with meter or meter-and-mix equipment. The two parts may be metered into a container for immediate mixing and application, or metered into a static mixer and inunediately dispensed to the adherends to be joined. A simple illustration of meter-and-mix equipment is the double-barrel syringe, which delivers the two parts of the adhesive to a nozzle containing static mixing elements. These elements are alternating right and left hand helices connected off center to each other. At the other end of the complexity spectrum is the equipment for automated assembly lines. 

M 72] [M 73] [P 65] The analysis of cross-sectional velocity profiles (water as fluid Re =12) shows that the intersecting structures have intricate gradient fields near the bars of the internals, while the helical device displays entrance and exit effects over more than one-quarter of the flow field (see [155] e.g. for fluid flow through macroscopic helical static elements) [2],... 

This barrier-embedded micro mixer was made with helical static elements, resembling the internals of a Kenics mixer, and barrier structures at the channel ceiling [3]. 

Some units can be adapted for solid-solid blending. The residence time in the units can be varied or adjusted, which makes them suitable for certain types of reactions. Figure 7-18 shows a cross-section of a flanged Kenics static mixer with four helical mixing elements, and Table 7-9 lists the characteristics of static mixers. 

Figure 7-18. Cross-section of flanged Kenics Static Mixer with four helical mixing elements. (Source Chemineer-Liquid-Agitation.)...

Static mixers, also called motionless mixers, consist of tubes or ducts in which stationary vanes (elements) have been installed to promote radial flow. There are many commercial types, some of which are shown in Eigure 8.5. A comprehensive review is available. See Thakur et al. (2003). They all function by inducing secondary flows perpendicular to the main, axial flow. A helically coiled tube without inserts also exhibits such flows and gives a limited improvement in performance. A series of helically coiled tubes where the axis of each successive coil is at a 90° angle to the previous coil axis can actually approach piston flow (see Nigam and Saxena, 1984). 

The latter type frequently operate in the melt phase to randomise the position of the minor component, by interrupting the laminar flow path of the polymer melt, causing repeated stream splitting and recombination of fluid elements, and generating substantially increased shear strain in the melt. Static mixers are normally introduced between the extruder and die, containing helical or other forms of element design, which divide and reunite flow streams in a controlled manner. 

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