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Static Mixers - What Process Engineers Need To Know




For the past week or so I had been doing my study on Static Mixers and that also made me think that I should be sharing what I have read and understood. The initial part which is a word description has been provided in the following text. However, the rough application guide for various commercial static mixer models and the pressure drop for the more popular static mixer models from manufacturers of repute such as Chemineer and Sulzer Chemtech could not be provided in the text. The excel workbook provided as an attachment repeats the text description provided below in addition to providing the rough application guide as a table and the pressure drop ratios for the popular commercial static mixer models. The excel workbook also lists out the leading manufacturers of static mixers and provides direct hyperlinks to their catalogs.

Static or motionless mixers use stationary shaped elements inside pipes or conduits to divide, divert,twist, and recombine flowing material. The dividing, stretching, and recombining processes lead to thinner and thinner striations in viscous materials to achieve uniformity. Molten polymers usually are in laminar flow and have no radial exchange when flowing. Thus temperature gradients can form and be propagated. Heating and cooling of these materials through the wall is very difficult because of the residence time distribution associated with the laminar velocity profile. Material at the center moves much faster than the material at the wall, and in addition, has less contact time because of the poor conductive heat transfer at the center. These devices would reduce radial thermal gradients that occur in polymer processing.

One of the first commercial units was the Kenics device. In the Kenics mixer, a set of twisted elements with left- and right-hand twists caused the material to move from the wall to the center and from the center to the wall. After traveling through a number of these elements, the fluid is homogenized with respect to age, composition, and temperature. These devices were called motionless mixers or static mixers because the mixer did not move, although the liquid did. The term static mixer was originally copyrighted by Kenics Corporation, but the term is now commonly used for all such in-line motionless mixers.

Over the years a large number of companies have produced static mixers all based on the principle of moving the streams radially by a series of metal baffles. These baffles may consist of twists of metal, corrugated sheets, parallel bars, small-diameter passages, or tabs sticking out from the wall. They are essentially plug flow devices with some small degree of backmixing, depending on the exact design.

Today static mixers are established in many different market segments and are used for a wide range of different applications. A common application for static mixers includes mixing two component adhesives (e.g. epoxy) and sealants. Other applications include wastewater treatment and chemical processing. Static mixers can as well be used in the refinery and oil & gas market for example for the desalting of crude oil. In the polymer production static mixers can be used for homogenization of polymer melts or for the uniform mixing of liquid additives to the molten polymer.

I would appreciate comments from the knowledgeable forum members for any further insight on static mixers, their applications and any other information which could prove useful to the chemical engineering community.

The spreadsheet can be downloaded here:

http://www.cheresour...s-need-to-know/


Regards,
Ankur.




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singaram mohan
Jun 01 2011 07:12 PM
Ankur

can you advice on selection of polymer coolers ,impact of temperature drop vs delta P on polymer properties ( for Pet)

thanks

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