Static mixers can be applied to a wide range of process operations, including dosing, dispersion, laminar flow heat exchange and emulsion formation. They offer many key benefits for combining liquids, gases and powders and they are tried, tested and trusted in many different industries. Mixing action is achieved by the continuous splitting, extension and transportation of the components. Motionless mixers use a series of precisely configured mixing elements to process the components. Differences in concentration, temperature and velocity are equalized over the flow cross-section. For further information go to principles of operation. Mixers are supplied as simple plain ended pipe sections, flanged with multiple injectors and sampling points, fitted in bends, or in square or rectangular section for ducts and open channels. They are manufactured in a wide range of materials, including carbon steel, stainless steel, exotic alloys, GRP, uPVC, cPVC, PTFE, etc.
The elements are made in various designs to suit different applications, and are available fitted into a range of housings, from high pressure to open-channel, making them ideal for all kind of industrial environments. The elements are fixed or removable and the necessary number of mixing elements for a specific application depends on the required homogeneity and on the volume flow ratio of the components.
The homogeneity requirement differs according to the particular mixing task and should specified by the final user in terms of variation coefficient CoV. Usually a CoV between 0.01 and 0.05 is a reasonable target for most applications. The lower the value of CoV the better the mixture quality.
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In case of two miscible liquids in laminar flow, the main mechanism in a static mixer is flow division. The elements are helical or pseudo-helical and are arranged in a series of alternating left and right hand 180 twists. The elements split the fluids entering in two streams and than rotate them through 180 degrees. The elements are in series in the mixer. As the number of streams or layers increases, the layer thickness decreases. Typically, 12 to 24 elements are required to provide a complete mix.
In case of two miscible liquids in a turbulent flow, the main mechanism is radial mixing: fluids are constantly moved from the pipe centre to the pipe walls and the fluid change direction with each succeeding element. To achieve a fully homogeneous mix in a turbulent flow 1.5 to 4 elements are sufficient.
In case of two immiscible liquids in a turbulent flow, the radial mixing mechanism reduces radial differences in velocity and in droplet sizes. This raises the surface area of contact between phases, improving the mixing. The disperser length necessary depends on the required contact time. For mass transfer processes in which equilibrium is quickly established, a length of 5 diameters is generally sufficient.
Drawing of Statiflo pipe mixer Series 100/150
Types and Applications
Static mixers are installed in thousand of process plants worldwide, providing the highest standard of mixing efficiency, reliability and economy.
The main applications are in the following fields:
Water and wastewater treatment:
Oil, gas and petrochemical industries
Continuous process industry:
Food and pharmaceutical
Lenntech can help you to design the mixer that best suits your application. Do not hesitate to contact us for a direct technical and commercial offer.
See also our web page on venturi principle and applications.