A static mixer is a precision engineered device for the continuous mixing of fluid materials, without moving components. Normally the fluids to be mixed are liquid, but static mixers can also be used to mix gas streams, disperse gas into liquid or blend immiscible liquids. The energy needed for mixing comes from a loss in pressure as fluids flow through the static mixer. One design of static mixer is the plate-type mixer and another common device type consists of mixer elements contained in a cylindrical (tube) or squared housing. Mixer size can vary from about 6 mm to 6 meters diameter. Typical construction materials for static mixer components include stainless steel,

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, PVC, CPVC and

polyacetal Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic ...

. The latest designs involve static mixing elements made of glass-lined steel.

Design

Plate type

Westfall 2800 Static Mixer with multiple injection ports

In the plate type design mixing is accomplished through intense

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

in the flow.

Housed-elements design

In the housed-elements design the static mixer elements consist of a series of baffles made of metal or a variety of

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. Similarly, the mixer housing can be made of metal or plastic. The housed-elements design incorporates a method for delivering two streams of fluids into the static mixer. As the streams move through the mixer, the non-moving elements continuously blend the materials. Complete mixing depends on many variables including the fluids' properties, tube inner diameter, number of elements and their design. The housed-elements mixer's fixed, typically

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elements can simultaneously produce patterns of flow division and radial mixing: * Flow division: In laminar flow, a processed material divides at the leading edge of each element of the mixer and follows the channels created by the element shape. At each succeeding element, the two channels are further divided, resulting in an exponential increase in stratification. The number of striations produced is 2ⁿ where 'n' is the number of elements in the mixer. * Radial mixing: In either turbulent flow or laminar flow, rotational circulation of a processed material around its own hydraulic center in each channel of the mixer causes radial mixing of the material. Processed material is intermixed to reduce or eliminate radial gradients in temperature, velocity and material composition.

Applications

A common application is mixing nozzles for two-component adhesives (e.g.,

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) and sealants (see Resin casting). Other applications include

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and chemical processing. Static mixers can be used in the refinery and oil and gas markets as well, for example in

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processing or for desalting crude oil. In polymer production, static mixers can be used to facilitate polymerization reactions or for the admixing of liquid additives.

History

The static mixer traces its origins to an invention for a mixing device filed on Nov. 29, 1965 by the Arthur D. Little Company. This device was the housed-elements type and was licensed to the Kenics Corporation and marketed as the Kenics Motionless Mixer. Today, the Kenics brand is owned by

National Oilwell Varco NOV Inc., formerly National Oilwell Varco, is an American multinational corporation based in Houston, Texas. It is a worldwide provider of equipment and components used in oil and gas drilling and production operations, oilfield services, a ...

. The plate type static mixer patent was issued on November 24, 1998, to Robert W. Glanville of Westfall Manufacturing.

References