Static mixer

A static mixer is a device for mixing two fluid materials. Most commonly, the fluids are liquid; however, static mixers are used to mix gas streams, disperse gas into liquid or disperse immiscible liquids. The device consists of mixer elements contained in a cylindrical (tube) or squared housing. These can vary from about 6 mm to 6 meters diameter. Static mixer elements consist of a series of baffles that are made from metal or a variety of plastics. Similarly, the mixer housing can be made from metal or plastic. Typical materials of construction for the static mixer components included stainless steel, polypropylene, Teflon, PVDF and polyacetal.

The overall system design incorporates a method for delivering two streams of liquids into the static mixer. As the streams move through the mixer, the non-moving elements continuously blend the materials. Complete mixing is dependent on many variables including the fluid properties, tube inner diameter, the number of elements, and their design.

Design

A static mixer's fixed, typically helical, 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 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

Today static mixers are established in many different market segments and are used for a wide range of different applications ^[1] A common application for static mixers includes mixing two component adhesives (e.g. epoxy) and sealants (see Resin casting). Other applications include wastewater treatment and chemical processing.^[2] Static mixers can as well be used in the refinery and oil and gas market, for example for the desalting of crude oil. In the polymer production static mixers can be used for polymerization reactions or for the admixing of liquid additives.^[3]

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.^[4] This device was licensed to the Kenics Corporation and marketed as the Kenics Motionless Mixer.^[5] Today, the Kenics brand is owned by Robbins & Myers, Inc.; however, there are also other suppliers of static mixers, including Sulzer Chemtech Ltd, Koflo Corporation, Statiflo and KOMAX Systems Inc.

References