Static Mixers

Chapter 1: What is a Static Mixer?

A static mixer is a form of mixer that uses forced flow to combine miscible and immiscible substances into a homogeneous mixture. A static mixer is made up of a tube that contains mixing blades or elements that change the direction and movement of the flow such that all fluids, gasses, and liquids blend. There are various ways that the fluids to be mixed enter a static mixer with pumps and gravity being two of the most common methods.

Unlike other forms of mixing, static mixers do not have any moving parts and do not require any form of maintenance, a factor that reduces energy consumption and removes the need for electrical components. They have helical obstructions that force the flow to blend. Known as inline mixers, static mixers are used in production operations and processing lines that have a continuous flow of materials. They can mix a constant and steady stream of liquids or gasses quickly and efficiently.

Chapter 2: How Static Mixers are Made

The simple design of static mixers belays their capabilities. Although they are normally made of heavy sturdy metals, certain varieties are made of plastics that are used for less challenging and demanding applications. The main components, the tube and mixing elements, are made of an assortment of materials that include high quality plastics and stainless steel with more modern mixing elements made of glass lined steel.

Housing

The housing for a static mixer can be made of plastic or metal. The types of material used depends on the types of fluids that will be mixed. The various designs of housings enable different uses of static mixers. In some instances, a static mixer is inserted into a pipe line as a means of mixing fluids that flow through the pipeline. The elements in the housing include helical elements that are secured to the walls of the housing such that they will not move down stream.

The shape of the housing is that of a cylinder that is very similar to a pipe. Materials used to manufacture the housing include stainless steel, aluminum alloys, titanium, thermoplastics, and Teflon. The type of material adds to the versatility of static mixers and the industry for which they are used. The food and beverage industries have stainless steel as the metal for the housing due to stainless steel’s corrosion resistance and non-porous surface.

The engineering of the housing is a key feature of static mixer design and requires careful planning since static mixers provide a high level of control over the mixing process. The degree of accuracy of a static mixer is developed during the design phase with consideration of the housing being a part of the initial process.

Mixing Elements

Static mixers use several forms of mixing elements, which are made of a wide variety of materials, including several forms of plastic, different metals, and Teflon. The toxicity of the fluids being mixed determines the strength, durability, design, efficiency, and type of construction material used to manufacture the elements, which can be blades, baffles or channels.

• Blades – Blades can take several different shapes, such as helical, twisted, or spiral. The choice of the types of blades is dependent on the required mixing effect. How the blades are arranged determines the degree of mixing that will occur and are designed to achieve the highest degree of mixing.

  

  
  

• Baffles – Baffles are plates or flat sheets attached to the side of the mixing tube and extend from one side of the tube across to the other side of the tube. They are attached diagonally in a crisscross pattern and block the flow such that the liquids divide, mix, and recombine. Baffles produce radial and axial flow and are ideal for blending liquids with a similar viscosity. They are made of twisted metals, corrugated sheets, parallel bars, small diameter passages, or various forms of tabs.

  

  
  

• Channels – Channel mixing elements can be square, narrow and deep, or wide to develop various velocity profiles. They can be custom designed with any form of rectangular cross section. Open channels ensure low head loss and allow debris to pass through. They are used with several different flow rates and are commonly used for chemical dosing. Channels are small, flow directing that evenly distribute the flow. Their mixing process is chaotic, which produces flow disturbances that increase mixing.

  

  
  

• Helical – Helical static mixers use alternating elements set at 90° where the first element rotates the flow while the next element reverses the direction of the flow. The design forces the flow to be inverted, moving the stream to the center of the pipe and back to the pipe wall in continuous motion. There are no dead spots for the products to hang up or be captured. The varieties of helical elements include jacketed, heated, and removable ones with differing edge seal types.

  

  
  

• Fin – Fin type static mixers have tapered and curved fins that are welded around the interior of the tube of the static mixer and are designed to invert the flow of liquids or gasses to rapidly mix them. In most designs, there is a second set of fins downstream from the first set that creates additional vortices with some versions having three sets of fins.

  

  
  

The types of static mixing elements listed above are a small fraction of the many designs and configurations of mixing elements, which are designed and engineered for specific purposes and applications. In many instances, manufacturers develop customized elements to meet the requirements of specialty gasses and fluids.

Chapter 3: Types of Static Mixers

The feature of static mixers that normally defines them is the types of elements that mix the materials in the flow, which include baffles, channels, blades, discs, and a wide variety of configurations. How these elements are arranged, placed, and designed determines the efficiency of the mixing process. Although the tube or pipe type of static mixer is the most common, there are other forms of static mixers that have been engineered to complete the same functions as the traditional form.

Wafer Static Mixers

Wafer mixers are very compact and complete the mixing process in a limited space for pipelines that are 2 inches to 120 inches (5.08 cm to 304.8 cm) in diameter. Their slim profile allows for simple drop-in installation with minimal pressure drop. Much like the larger tube or pipe type of static mixer, wafer static mixers are motionless full pipe mixers that can mix up to six fluids.

The original purpose of wafer static mixers was to meet the needs of the desalination industry, which removed salt from water. Beyond their original purpose, they have expanded to becoming an integral part of industrial processes. Recent designs of wafer static mixers are used for turbulent flow dosing and blending applications.

Venturi with Static Mixer

The purpose of a venturi tube used with a static mixer is to dissolve ozone into water by transforming the ozone into fine bubbles. The static mixer is installed after the venturi, which increases the water pressure, from which the water enters the static mixer where the elements of the static mixer breakdown the ozone gas bubbles into smaller bubbles to increase the surface area of the bubbles. As the size of the bubbles decreases, they are dissolved in the water. The purpose of the venturi is to pressurize the water such that the static mixer can make the ozone gas more soluble.

Jet Static Mixer

Jet static mixers use helical movement for in line mixing of fluids. It is a continuous mixing process that meets process conditions and the properties of the fluids being mixed. Jet static mixers guarantee low pressure drop, highly efficient mixing, acceptable mixing time, and a high grade of mixing. In jet mixing, a fast-moving liquid is injected into a slow-moving liquid with the difference in the velocity of the liquids creating the mixing in the static mixer. Jet static mixers are used for mixing, blending, solid suspensions, and homogenization.

With jet static mixers, there is a pressure loss as a fluid moves through the mixing elements, which makes it possible for jet static mixers to be used for laminar flow and turbulent flow. With laminar flow, mixing is a combination of flow division and flow re-orientation. In turbulent flow, the elements of the jet static mixer cause turbulence in the flow. The variables that determine the number of elements in a jet static mixer are the flow rate and the viscosity of the fluid.

Kenics Static Mixer

Kenics static mixers are helical static mixers that divide, stretch, and reorient the flow to mix and blend fluids with minimal pressure drop. They produce rapid mixing by creating circular patterns that reverse the direction of the flow at the intersection of each element. The design of Kenics static mixers avoids material blockages that are found in other static mixers due to the pattern of the helical elements, which guides fluids to the pipe walls and back to the center for continuous mixing.

The efficiency of the mixing with a Kenics static mixer is due to the right and left hand elements that increase flow velocity reversal and division. The process eliminates radial gradients in temperature, velocity, and material composition. The structure of the helical elements of a Kenics static mixer twists a fluid as part of the mixing process.

Spiral Static Mixers

Spiral static mixers are disposable or single use mixers for two-part fluids using 180° helical twists that alternate at a right to left rotation. The elements in a spiral static mixer are joined such that the leading and trailing edges are perpendicular. Spiral static mixers are made of highly durable plastics with a bell-shaped inlet for pouring the two materials to be mixed into the static mixer. The housing and elements of a spiral static mixer are made of plastic but can be reinforced with a metal jacket when the pressure in the nozzle is greater than 150 psi.

Although in all cases spiral static mixer elements are made of plastic, there are versions that use spiral elements that are placed inside stainless steel housings. In this type of spiral static mixers, the elements, as with other versions, are disposable and can be removed from their housing for cleaning and maintenance.

The main attraction of spiral static mixers is their wide variety of mixing elements, tip styles, and element diameters, which makes it possible to select one that perfectly fits an application or process. They are a low cost mixing solution for small mixing projects.

Jacketed Static Mixers

Jacketed static mixers are used when the mixing process requires heating or cooling or when a set temperature has to be maintained. The application of the jacket is designed to add heat or remove it in order to achieve the parameters for the mixing process.

Teflon Lined Static Mixers

Teflon lined static mixers are used for the mixing of harsh chemicals. Their specially designed lining prevents corrosion and damage to the mixer. They are commonly used in the chemical processing industry for mixing concentrated acids and other forms of toxic or dangerous chemicals.

The Teflon coating of the interior of a static mixer extends its service life making it possible to use the mixer with high pH levels and aggressive harmful chemicals. The application of the coating includes the flanged ends of the static mixer, the injection port, the elements, and threaded ends with mixing elements coated with Teflon that is 25% glass filled.

Heat Exchanger Static Mixers

Heat exchanger static mixers are used for heat transfer in laminar flows and are used for heating and cooling of viscous materials. Static mixers exchange wall and bulk fluid material enhancing heat transfer in accordance with the type of static mixing elements being used, tube size, the viscosity of the fluid, process conditions, and certain fluid properties.

The geometric structure of the static mixing elements influences the heat transfer process with each design having positive and negative qualities. The most cost effective of the elements is the helical elements with alternating right and left bowtie type twists. They are the most cost effective and efficient. The bent tube static mixing structure of a static mixer has similarities to a heat exchanger and is used in a monotube configuration.

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Chapter 4: The Static Mixer Mixing Process

Static mixers, also referred to as motionless mixers, are one of the least expensive but highly effective types of industrial mixing tools. The first static mixers were developed in Germany by Bayer AG, a chemical and pharmaceutical company, that used the mixers in their polymer plants. The process was further developed by a chemical company in Switzerland.

The simple structure of static mixers makes them highly efficient and capable of mixing several types of fluids. They are engineered and designed to mix a wide array of materials by adjustments to their material structure, element design, and size, which can vary according to the size of a pipeline. In most cases, the simple process of a static mixer has been a cost saving for industrial mixing operations and removes the need for more complex mixing methods.

Types of Fluid Flow

When discussing the process of a static mixer, it is important to understand the different types of flow, which influences the type of static mixer and its elements. There are many characteristics to fluid flow with turbulent and laminar being the most common but not the only types. When clients are working with manufacturers in the selection and design of a static mixer, the type of fluid, such as its viscosity and velocity, are two of the initial factors. What is considered next is the type of flow, since flow movement determines the effectiveness of the mixing process of a static mixer.

• Laminar Flow – Laminar flow is a very smooth flow that has parallel layers of fluid particles where the various layers do not mix. It is a predictable flow pattern that is streamline and even with a low flow velocity, high viscosity, and unobstructed flow pattern.
• Turbulent Flow – Turbulent flow can best be described as being chaotic and irregular with eddies, vortices, and changes in velocity and pressure. Common characteristics of turbulent flow are high velocity, low viscosity, and various forms of disturbances and obstacles in the flow path.
• Transitional Flow – Transitional flow is a combination of laminar flow and turbulent flow where the flow pattern jumps between the two patterns. As with laminar and turbulent flow patterns, transitional flow is influenced by flow velocity, liquid viscosity, and the texture of the pipe through which it moves.

Static Mixer Mixing

Static mixers have no moving parts and rely on the placement of the various types of mixing elements to blend and mix liquids, fluids, and gasses that pass through the mixer. The placement of the mixing elements causes the material flow to move in certain ways to initiate the mixing process. For turbulent flow patterns, the mixing process is splitting and radial while the process for a laminar flow is splitting.

Although static mixers operate without the need of power, they do cause a pressure drop, which is compensated for by an upstream pump. In the majority of cases, static mixers provide efficient mixing with a very small pressure drop.

Laminar Mixing

The laminar mixing process involves repeated division, transposition, and recombining of the liquid flow. The identical mixing elements of the static mixer are spread into several layers. An increase in the number of mixing elements makes each layer finer creating a more homogenous mix.

Turbulent Mixing

Turbulent mixing is very common in industrial applications. Mixing is achieved by rotating and shearing the layers in the flow, which happens with the reversal of the rotation of the liquid. Small shearing is necessary when the pitch between the rotations can be adjusted. As the pitch slows the rotation, extra mixing occurs in the static mixer. The mixing elements in a static mixer generates eddy currents in the flow. Inhomogeneity is removed by cross currents created by the mixing elements.

Static mixers are designed to mix fluids or gasses since the mixing elements would block powders or solids and become clogged with material build up. The mixing process of a static mixer causes turbulence in the liquids or gasses that enter it. The materials being mixed are divided, recombined, and divided again multiple times such that the stream exiting the mixer is homogeneous in regard to its concentration, temperature, velocity, and is equalized.

The many variations in static mixer design are due to the need to meet the requirements of a manufacturer’s application. In general, helical element static mixers are used by the chemical, pharmaceutical, and food industries while Kenics, tab, and wafer static mixers are used by the water industry.

There are variations as to how liquids, fluids, and gasses enter a static mixer. In some cases, blowers or pumps are used to move materials along to the mixing elements at the necessary volumetric flow rate and pressure. The sizes of static mixers vary in accordance with the application for which they are used.

Positioning of a Static Mixer

Static mixers can be installed horizontally, vertically, on an angle, or any other type of configuration since they do not have any moving parts and do not require any form of power supply. As with other factors that govern the use of static mixers, their positioning is in regard to the type of fluids or gasses that will be mixed.

Chapter 5: Static Mixers Compared to Dynamic Mixers

Modern industrial applications require the blending and mixing of fluids and gasses to ensure the quality of products. The two most used methods of mixing are dynamic and static, which can achieve the same mixing results using different methods. Although both methods are productive and advantageous, they have their drawbacks and disadvantages.

Static Mixers

Static mixers are immobile mixers with baffles, blades, and other forms of elements that are arranged in a pipe or tube that cause turbulence in fluids or gasses for continuous mixing. They are simple inline devices that are capable of mixing and blending miscible and immiscible fluids.

Advantages of Static Mixers

• Low cost
• Do not require maintenance
• No energy consumption
• No moving parts
• Small footprint
• Easy installation
• Long service life

Dynamic Mixers

The most notable difference between static mixers and dynamic mixers is the electrical power that is used to power dynamic mixers. Electrical power is required by a dynamic mixer in order for it to be able to create the turbulence of the mixing process. They have a rotating shaft with various forms of impellers that blend and mix materials as they spin at high speed. The mixing process for dynamic mixers is very aggressive due to the fast rotation of the impellers. In addition, dynamic mixers, unlike static mixers, require more space and have a larger footprint.

Advantages of Dynamic Mixers

• Ideal for batch mixing
• Capable of mixing high viscosity materials
• Provide high shear mixing
• Impellers come in several forms, sizes, and designs

When examining static mixers and dynamic mixers, it is important to understand that static mixers rely on the design of the elements of the mixer in order to achieve optimal mixing without the use of any form of mechanical force. The lack of power and mechanical force is the aspect of static mixers that differentiates them from dynamic mixers, which rely on mechanical force and motion to complete the mixing process.

In addition, static mixers cost less, have a smaller footprint, have a simple design, and require very little maintenance. Dynamic mixers are large complex devices that are subject to mechanical failure. They have motors that rotate a shaft that is attached to impellers and are capable of completing demanding mixing applications. Unlike static mixers, dynamic mixers are capable of mixing powders, dry materials, and solids that would clog or block a static mixer.

Chapter 6: Uses for Static Mixers

The many advantages of static mixers make them an ideal tool for several industries. Their simple design, ease of installation, and reliability enables users to apply them to various forms of fluids, liquids, and gases. The fact that all forms of static mixers can be adapted to a variety of conditions has enhanced their use and made them an attractive, money saving investment.

Static mixers are used in the chemical, wastewater treatment, food and beverage, and pharmaceutical industries due to their ability to blend and mix miscible and immiscible fluids with varying viscosities. The flexibility and adaptability of static mixers are characteristics that make them ideal for modern manufacturing.

Chemical Industry

It can be easily assumed that static mixers would be a perfect fit for the chemical industry, which has to blend and mix chemicals, additives, and dyes as part of chemical production. Static mixers ensure consistent mixing during polymerization, emulsification, and reaction kinetics. The precision of static mixers improves product quality, decreases reaction times, and improves overall efficiency.

Water and Wastewater Treatment

One of the primary uses of static mixers is in the wastewater treatment industry and was one of the initial uses of wafer static mixers. In the water and wastewater industry, static mixers are used for chemical dosing, pH adjustments, coagulation, and flocculation. They ensure proper blending and effective treatment processing as well as the removal of contaminants.

Pharmaceutical Industry

As with the chemical industry, the pharmaceutical industry involves a great deal of mixing and blending of chemicals, which necessitates precision and accurate processing. Pharmaceutical products require homogeneous mixing of ingredients (APIs), excipients, and other substances. Errors in the mixing process can lead to catastrophic results and danger to the general population. Consistent blending results in the proper texture, taste, quality, and appearance of a final product.

For the pharmaceutical industry, static mixers are made of stainless steel due to government regulations regarding hygiene and uncontaminated conditions. Since static mixers are sealed in a pipeline, they do not require the type of cleaning that is related to dynamic mixers due to being isolated from the environment.

Food and Beverage Industry

The types of mixing that is related to the pharmaceutical industry also applies to the food and beverage industry as well as the regulations relating to hygiene and sterility. Since products produced by the food and beverage industry are used by the public, the quality and appearance of the products has to meet the highest standards. This factor has led to the wide use of static mixers that are capable of blending and mixing any form of fluid or liquid to create a flavorful and homogeneous product.

Petrochemical Industry

Static mixers are ideal for the petrochemical industry that deals with volatile and combustible chemicals. Since static mixers are contained in a pipeline away from equipment and workers, the blending and mixing process is isolated, safe, and contained. Fuels, additives, and lubricants are mixed safely, completely, and efficiently to ensure conformity with product parameters. The use of static mixers ensures the proper performance, stability, and quality of fluids and components.

The Reasons Industries Depend on Static Mixers

Manufacturers are motivated to produce quality products at a reasonable price. In order to achieve these goals, it is necessary for producers to evaluate their processes to ensure they are producing their products with the utmost efficiency and quality. Static mixers have found a place in a wide range of industries for three reasons.

1. Simple Operation – Static mixers are immobile devices that operate independently without the need for power or moving parts. Through the use of different types of elements, they manipulate the flow stream to achieve a homogeneous mix, simply and reliably.
2. Maintenance – Since static mixers do not have any motors or moving parts, they do not require regular maintenance. They operate continuously without failing, which can stop a process and create downtime.
3. Uniform Mixing – The miracle of static mixers is how they are able to uniformly mix fluids or gasses to achieve the highest level of blending. Using their elements, static mixers split, redirect, and recombine liquids multiple times to create a thoroughly mixed blend.

Conclusion

• A static mixer is a motionless mixing device that uses various types of elements to mix fluids, liquids, and gases.
• The simple structure of static mixers includes a housing, tube, or pipe that contains mixing elements that are helical, plates, channels, tabs, or wafers that disturb the flow of materials and cause them to blend and mix.
• Static mixers operate by the inertia of fluids or gasses and cause turbulence in them, which forces the fluids or gasses to combine, divide, and combine multiple times to produce a homogenous mixture.
• The wide use of static mixers is due to their ability to be easily installed and the fact that they do not require any form of maintenance. They can be installed in any position and can be customized to fit the needs of any solution or combination of materials.
• Static mixers are made from a wide variety of materials, which vary from highly durable and resilient plastics to different types of metals. The selection of the type of static mixer is dependent on the types of materials that are to be mixed, their viscosity, and velocity.

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