Static mixer

Demonstration of a static mixer in Kenics design

Mixing of two adhesive components in a disposable static mixer

Section - one screw turn on the right (180 °) and one on the left (180 °); both screw turns are rotated 90 ° against each other

A static mixer or static mixer is a device for mixing of fluids , in which alone the flow movement causes mixing and that does not have moving elements. It consists of flow-influencing elements in a pipe. These alternately divide the material flow and then bring it back together again, whereby mixing is achieved. Static mixers are suitable for the combinations liquid / liquid, gaseous / gaseous and liquid / gaseous, possibly also for bulk goods. Another application is the homogenization of just one substance in terms of composition and temperature.

Structure and functionality

Mixing of the laminar flows in the Kenics mixer

Radial mixing

Static mixer for industrial applications, type Sulzer-SMX

The static mixer consists of lined up elements, which are usually screw, lamella or grid-shaped. The fluids to be mixed are pressed into the mixer together and in the desired mixing ratio. The elements divide the material flow, twist the flows and bring them together again. If the first element divides the two-layer substance mixture that is pumped in, at least four layers result after the element has been brought together. After the next there are eight layers, then 16 and so on. With each step, better mixing is achieved. Generally applies to the number of layers

{\ displaystyle N = N_ {a} k ^ {n}.}

${\ displaystyle N_ {a}}$ is the number of layers at the beginning, the number of channels, usually two, the number of mixer elements. ${\ displaystyle k}$ ${\ displaystyle n}$

In addition to this effect, which occurs solely through laminar flow, there is also a radial mixture of the individual layers with one another, especially when turbulent flows occur.

There are several dozen different mixer types, some examples are:

Kenics mixer : It consists of sheet metal twisted by 180 °. Each helix is offset by 90 ° to the previous one and has the opposite direction of rotation.
Sulzer SMV mixer : Corrugated lamellas guide the currents so that they cross each other.
Sulzer SMX mixer : This mixer has a large number of framework-like crosspieces.
Fluitec CSE-X / 6-12 mixer :: This mixer has six tapered, crosswise arranged webs and has openings in the edge zones. This leads to a high mixing performance with a significantly reduced pressure loss.
Fluitec CSE-XR mixer-heat exchanger : In addition to the mixing elements, this static mixer has an integrated tube bundle for heat exchange.
Ross ISG mixer : The mixer is divided into segments by modules. The material can only get from one segment to the other through holes in the modules. The beginning and end of the boreholes are arranged so that mixing takes place. The number of channels (holes) is four. ${\ displaystyle k}$

The mixers are made either from metal suitable for the media or from plastic, then usually as single-use products.

interpretation

The selection of the suitable mixer type and the optimal geometry is primarily determined by:

the properties of the fluids to be mixed, especially the viscosity and density
the desired mixing quality
the available installation length and the pipe diameter
the desired operating pressures
the flow rate
the residence time in the mixer for reactive mixtures.

The coefficient of variation is usually used as a measure of the mixing quality , with the mean concentration of a component and its standard deviation. An ideal mixing would therefore exist at. The coefficient of variation decreases exponentially with increasing related mixer length , the ratio between absolute mixer length and diameter of the mixer. I.e. the longer the mixer and the smaller the diameter, the better the mixing effect. If the flow velocity is so high that the Reynolds number reaches the value 100–200, which is critical for this mixer, turbulent flows occur. These further improve the mixing quality. ${\ displaystyle \ sigma / {\ bar {c}}}$ ${\ displaystyle {\ bar {c}}}$ ${\ displaystyle \ sigma}$ ${\ displaystyle \ sigma / {\ bar {c}} = 0}$ ${\ displaystyle L_ {m} / D}$ ${\ displaystyle L_ {m}}$ ${\ displaystyle D}$ ${\ displaystyle Re}$

The following measured values are available for Kenics and Sulzer SMV mixers :

	${\ displaystyle L_ {m} / D}$ for Kenics	${\ displaystyle L_ {m} / D}$ for Sulzer SMV
${\ displaystyle \ sigma / {\ bar {c}} = 10 ^ {- 1}}$ , laminar flow	17th	9
${\ displaystyle \ sigma / {\ bar {c}} = 10 ^ {- 1}}$ , turbulent flow	3.7	1.1
${\ displaystyle \ sigma / {\ bar {c}} = 10 ^ {- 2}}$ , laminar flow	29	18th
${\ displaystyle \ sigma / {\ bar {c}} = 10 ^ {- 2}}$ , turbulent flow	7.3	1.9

An improvement in the mixing quality by reducing the diameter has its limits in the resulting increase in pressure loss in the mixer. As the pressure loss increases, so do the necessary delivery and operating pressures. The following applies in the laminar area ${\ displaystyle D}$ ${\ displaystyle \ Delta p}$

{\ displaystyle \ Delta p = \ zeta Re {\ frac {\ eta v_ {m} L_ {m}} {2D ^ {2}}},}

where represents the mean flow velocity, the dynamic viscosity of the fluid and the pressure loss coefficient . Halving the diameter means quadrupling the pressure loss or even a sixteen-fold increase if the volume flow is to remain the same by increasing the flow velocity. ${\ displaystyle v_ {m}}$ ${\ displaystyle \ eta}$ ${\ displaystyle \ zeta}$

The product is constant in the laminar area and depends on the mixer type: ${\ displaystyle \ zeta Re}$

	Kenics	Sulzer SMV	Sulzer SMX	Ross ISG	empty pipe
${\ displaystyle \ zeta Re}$	450	5600	4000	12000	64

From the context it follows that one z. B. can build an X mixer and Sulzer SMV as a very compact mixer. In comparison, however, the Sulzer SMV mixer shows a high pressure loss. For highly viscous media, X and Kenics mixers with the lower pressure losses are more suitable.

Advantages and disadvantages

Compared to dynamic mixers such. B. agitators , static mixers have some advantages. They are inexpensive, do not take up much space, are maintenance-free due to their design, do not require an energy supply and can be integrated directly into conveyor lines. Above all, they make it possible to mix components continuously and with a short, little varying residence time over a wide viscosity range. When stirring in separate mixing containers, however, only batch processes are possible: the containers must first be filled, then the actual mixing process takes place and only then is the finished mixture available. Especially when processing curable substances with limited pot life such. B. Cast resin , static mixers are advantageous. The material is filled or applied directly from the mixer into the mold, so the components only come into contact with one another immediately before processing, so there is no need to add to the stock.

The disadvantage is that it is normally not possible to influence the mixing intensity, while the speed of the stirrer can be changed. When processing hardening materials, static mixers can become clogged during production interruptions. Therefore, they have to be rinsed or made as single-use products.

History of origin and applications

Disposable static mixer and cartridge for manual processing of a two-component system

As early as 1924, a helix was used in a pipe for mixing purposes. The first patent application for a static mixer based on the Kenics principle was made in 1965 by Arthur D. Little . The purpose was the mixing of synthetic resins in small amounts, e.g. B. for repair work. The Kenics Corporation then manufactured these mixers from stainless steel under license. From the 1970s, they could also be made from plastic as single-use products.

In addition to processing resins, adhesives, sealing compounds, etc., the range of applications for static mixers today includes all process engineering areas with mixing processes, e.g. B. in the chemical industry , food industry , water and wastewater treatment (e.g. enrichment of water with oxygen), oil and gas industry. In plastics technology, static mixers are used in potting systems and for mixing polymer melts .

literature

FA Streiff: Static mixing. In: Matthias Kraume (Ed.): Mixing and stirring: Fundamentals and modern processes. Wiley-VCH, Weinheim 2003, ISBN 978-3-527-30709-8 ( limited preview in Google book search)
Alain Georg and Martin B. Däscher: Chemical reactions in tubular reactors and static mixers - homogeneity, residence time behavior, heat dissipation, design, application examples . Chemie Ingenieur Technik, Volume 77, Issue 6, pages 681-693, June, 2005 edition. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2005.

Web links

Commons : Static Mixer - collection of pictures, videos and audio files

Individual evidence

↑ ^a ^b ^c ^d ^e F. A. Streiff: Static mixing. In: Matthias Kraume (Ed.): Mixing and stirring: Fundamentals and modern processes. Wiley-VCH, Weinheim 2003, ISBN 978-3-527-30709-8 ( limited preview in Google book search)
^ Hans Günther Hirschberg: Handbook of process engineering and plant construction: chemistry, technology and economic efficiency. Springer, Berlin / Heidelberg / New York / Barcelona / Hong Kong / London / Milan / Singapore / Tokyo 1999, ISBN 3-540-60623-8 , pp. 863–867 ( limited preview in Google book search)
↑ ^a ^b ^c ^d ^e Marko Zlokarnik: Mixing technology : theory and practice. Springer, Berlin / Heidelberg / New York / Barcelona / Hong Kong / London / Milan / Singapore / Tokyo 1999, ISBN 978-3-540-64639-6 , pp. 286–291 ( limited preview in Google book search)
↑ Patent application EP 2 286 904 A1: Static mixing device for flowable substances. Registered on August 12, 2009, published on February 23, 2011, applicant: Fluitec Invest AG, inventor: Alain Georg u. a. ( Online at epo.org ).
^ Matthias Kraume: Transport processes in process engineering: Fundamentals and implementations of equipment. Springer, Berlin / Heidelberg / New York, 2003, ISBN 978-3-540-40105-6 , pp. 529–533 ( limited preview in Google book search)
↑ Manfred H. Pahl, Edgar Muschelknautz: Use and design of static mixers. In: Chemical Engineer Technology. Volume 51, No. 5, May 1979, Wiley-VCH, pp. 347-364
↑ US Patent 1626487 Emulsifier , filed on January 10, 1924 by David Warren ( PDF on freepatentsonline (190 kB) )
↑ US Patent 3286992 Mixing Device , filed on November 29, 1965 by Constantine D. Armeniades, Wiliam C. Johnson and Thomas Raphael for Arthur D. Little Inc. ( PDF on freepatentsonline (265 kB) )
↑ Irving J. Arons: The Disposable "Motionless Mixer". In: ADL Chronicles - A presentation of the products and inventions that came out of the laboratories of Arthur D. Little, Inc.ADL Chronicles, July 23, 2008, accessed May 7, 2012 .
^ Friedrich Johannaber, Walter Michaeli : Injection molding manual. 2nd Edition. Hanser, Munich 2004, ISBN 3-446-22966-3 , pp. 820–822 ( limited preview in Google book search)

[streiff-1] F. A. Streiff: Static mixing. In: Matthias Kraume (Ed.): Mixing and stirring: Fundamentals and modern processes. Wiley-VCH, Weinheim 2003, ISBN 978-3-527-30709-8 ( limited preview in Google book search)

[2] Hans Günther Hirschberg: Handbook of process engineering and plant construction: chemistry, technology and economic efficiency. Springer, Berlin / Heidelberg / New York / Barcelona / Hong Kong / London / Milan / Singapore / Tokyo 1999, ISBN 3-540-60623-8 , pp. 863–867 ( limited preview in Google book search)

[ruehrtechnik-3] Marko Zlokarnik: Mixing technology : theory and practice. Springer, Berlin / Heidelberg / New York / Barcelona / Hong Kong / London / Milan / Singapore / Tokyo 1999, ISBN 978-3-540-64639-6 , pp. 286–291 ( limited preview in Google book search)

[4] Patent application EP 2 286 904 A1: Static mixing device for flowable substances. Registered on August 12, 2009, published on February 23, 2011, applicant: Fluitec Invest AG, inventor: Alain Georg u. a. ( Online at epo.org ).

[5] Matthias Kraume: Transport processes in process engineering: Fundamentals and implementations of equipment. Springer, Berlin / Heidelberg / New York, 2003, ISBN 978-3-540-40105-6 , pp. 529–533 ( limited preview in Google book search)

[6] Manfred H. Pahl, Edgar Muschelknautz: Use and design of static mixers. In: Chemical Engineer Technology. Volume 51, No. 5, May 1979, Wiley-VCH, pp. 347-364

[7] US Patent 1626487 Emulsifier , filed on January 10, 1924 by David Warren ( PDF on freepatentsonline (190 kB) )

[8] US Patent 3286992 Mixing Device , filed on November 29, 1965 by Constantine D. Armeniades, Wiliam C. Johnson and Thomas Raphael for Arthur D. Little Inc. ( PDF on freepatentsonline (265 kB) )

[9] Irving J. Arons: The Disposable "Motionless Mixer". In: ADL Chronicles - A presentation of the products and inventions that came out of the laboratories of Arthur D. Little, Inc.ADL Chronicles, July 23, 2008, accessed May 7, 2012 .

[10] Friedrich Johannaber, Walter Michaeli : Injection molding manual. 2nd Edition. Hanser, Munich 2004, ISBN 3-446-22966-3 , pp. 820–822 ( limited preview in Google book search)