Agitators
Agitators are equipment used in homogenizing media inside a tank. It works by rotating the impeller at its immersed end at a controlled speed or revolutions per minute (rpm). The work exerted by...
Please fill out the following form to submit a Request for Quote to any of the following companies listed on
In this article, you will learn about high shear mixers. This comprehensive guide offers you the following:
High shear mixers, also known as high shear reactors (HSRs), rotor-stator mixers, and high shear homogenizers, are mixers that are used to emulsify, homogenize, disperse, grind and dissolve immiscible mixtures. They have high rotor tip speeds, high shear rates, localized energy dissipation rates, and use more power than ordinary industrial mixers.
Shearing forces is the stress that mixing blades or impellers give to liquids, solids, and materials that are being mixed. In liquid or powder mixers, a high speed rotor pushes the material toward a stationary stator, which creates a shear by pushing different parts of the material in opposite directions in the same plane. The uniqueness of this technique makes it possible to mix liquids, solids, or gases that can not be completed using ordinary mixing techniques.
Consumer products that have ingredients that are immiscible require the use of a high shear mixer and include salad dressings, paints, cosmetics, detergents, shampoo, and various forms of ointments. The multiple types of uses for high shear mixers include liquid to liquid emulsification, different viscosity liquids, solid to liquid, powder to liquid, and particle reduction mixing. High shear mixers have become a necessity and integral part of industrial operations for pharmaceuticals, chemicals, health care products, and cosmetics.
A fluid is any liquid or gaseous substance that is free to flow and is not bound nor restricted by any surface effects. The study of the behavior of fluids is known as fluid mechanics. Fluids, like solids, can experience force, stress, or pressure. A flowing fluid experiences shear stress, which is the driving principle of high shear mixers.
Shear stress in fluids is primarily caused by friction between the fluid molecules due to viscosity. Friction between fluids and a moving body also creates shear stress.
The moving body and the fluid molecules in direct contact have the same velocity which is known as the no-slip condition. Intermolecular forces act between the fluid molecules and the surface of the body, known as the boundary layer, resulting in attraction. Once a steady state is achieved, the velocity profile is linear. There is no more acceleration and no more force to deform or shear the fluid. Motion is transferred across each layer of the fluid and is countered by its viscosity.
Laminar flow happens when the fluid is flowing evenly without any disruption across these layers. Adding different bodies to cause shearing forces acting in different directions disrupts this flow. This type of flow, known as turbulent flow, is chaotic causing mass transfer across the fluid layers. Uneven flow across layers of fluid also causes mass transfer. This is effective in breaking up droplets suspended in the mixture causing emulsion, dispersion, and homogenization of the components.
High shear mixers generally have two main parts: the rotor and the stator. This assembly is known as the mixing head or generator. The rotor accelerates the fluid tangentially. The inertia of the fluid, keeps it from flowing together with the rotor. The fluid flows towards the shear gap or the region between the rotor tip and the stator. Inside the shear gap, high velocity differentials and turbulent fluid flow is present producing high shear rates.
The rotor and stator profile, their configuration relative to one another and other features such as holes and slots, contribute to creating the desired fluid flow depending on the application. Below are some of the processes performed by high shear mixers.
This requires liquid droplets to be uniform in size, completely distributed to create a mixture with one continuous phase. The liquid in the form of droplets are in the dispersed phase, while the liquid where the droplets are suspended is the continuous phase. In an emulsion, natural separation happens between the dispersed and continuous phases. This is particularly observed in immiscible liquids such as oil and water. Oil is nonpolar, and as a result they are not attracted by water molecules. Also, oils are usually lighter than water enabling them to float on the surface. Because of these properties, oil tends to naturally separate from water. The objective of the high shear mixer is to continuously break down these droplets before natural separation happens.
Another type of emulsion is a miscible liquid-to-liquid mixture but with different viscosities. Adding low viscosity droplets to a high viscosity solvent requires more mixing time and controlled component addition rates.
A suspension mixture has solid particles that are large enough to settle down which cannot be dissolved completely in the mixture. The objective is the same as the emulsion homogenization, to break down the large solid particles into smaller ones while evenly dispersing it into the medium.
One problem in this process is the difficulty in wetting the solid particles. These solid particles tend to form on the surface of the solvent. This is due to the surface tension of the liquid and the hydrophobic property of the particles. This will be discussed further in the topic of in-line high shear mixers.
In this application solid or semi-solid materials are milled down into finer particles either in a solution or fine suspension. The size reduction depends on the hardness of the product.
This involves mixing solid products with a binder or granulating liquid. As the powder and binder are blended, the mixture is continuously shaped producing high-density granules.
Most manufacturers advertise their equipment of being able to do all these functions. This is partially true; any mixer can do these but at low efficiencies. High shear mixers are carefully designed considering the phase of the dispersed particles, the fluid viscosity, the required particle size, and so on. Computational fluid dynamics (CFD) analysis is done to simulate the operation of the mixer to determine the optimum geometry of the rotating and stationary parts.
Using CFD analysis to accurately simulate actual conditions is complex and requires scholar level type of study. This makes approach on the design of high shear mixers empirical; focused on development through application specific testing for different products and manufacturing setups.
High shear mixers are classified according to their configuration, which include batch, in-line, powder induction, and ultra-high. Although the basic methodology between the different types varies, the shearing process remains the same for all types. Manufacturers rely on high shear mixers to blend viscous materials into homogeneous and agglomerate products that will not break down.
This type mixes all components by batch and in large volumes in a tank or vessel. Charging of the components is usually done at the top of the vessel. Batch high shear mixers can also be configured to have only one mixing head that can be lifted and suspended serving several vessels. Batch mixing is said to process faster than in-line high shear mixers with the same power rating. One problem in this system is the cleaning process between batches with varying formulations. This problem is particularly evident in viscous mixtures. Residues from the previous batch can become a contaminant to the next batch. To solve this problem, clean in place (CIP) systems are employed.
In-line mixers are integrated into a processing system such that ingredients to be mixed flow through the mixer. The rotor stator of an in-line shear mixer is positioned perpendicular to the flow of the ingredients to create an exceptionally intense shearing force.
The components of an in-line mixer are in a chamber with an inlet and an outlet and uses centrifugal force as a pump to drive the mixture through the chamber. The chamber is tightly closed and sealed to prevent contamination. Since in-line mixers are part of a product stream, the mixing process is controlled and monitored with the product flowing from the mixer being monitored, a design that enables operators to modify the mixing parameters in real time.
With an in-line high shear mixer, a mixing pot or vessel is used to collect and combine all raw materials, which can be a simple mixing chamber or a batch mixer.
From the static head, the pre-mixed materials are transferred into the in-line high shear mixer. The static head provides self-priming. As the in-line high shear mixer homogenizes the materials, the mixture is transported to downstream equipment or recirculated back into the mixing chamber. Once the desired particle size and a continuous phase is attained, recirculation is stopped, and mixed materials are diverted to downstream processes.
The positioning of an in-line high shear mixer in the processing system ensures continuous flow of ingredients for seamless and uninterrupted mixing. The process is further enhanced by the positioning of the rotor stator perpendicular to the flow of ingredients, which provides a high degree of precision that is required by the pharmaceutical, cosmetic, and personal care industries.
The compact design of in-line shear mixers gives them a small footprint for easy placement in a processing system, which makes them a space saving solution. Regardless of their compact size, their design makes them exceptionally efficient and productive.
This type of high shear mixers uses vacuum systems to draw powdered components directly into the mixing head. A vacuum is generated on the rotor-stator assembly drawing the powder from a hopper. This solves several problems that arise when dealing with difficult to process powders.
When charged into the mixing chamber, some powders quickly agglomerate upon contact with the liquid. Clumps tend to form on the surface of the liquid which will then require higher mixing speed to form a vortex. The vortex is required to draw the powders to the mixing head. To mitigate this, these powdered components need to be added carefully and slowly to prevent agglomeration on the surface. However, adding too slowly can cause the continuous phase to reach its target parameters without thoroughly combining dispersed particles that are still undissolved and floating on the surface. In a mass production scale, this directly impacts throughput and in turn, profit margins.
Other scenarios that can happen are the irreversible changes in viscosity and degradation from heating, making the mixture thinner or thicker than the desired viscosity. This is evident in non-Newtonian liquids. Shear-thinning liquids become less viscous when subjected to shear, while shear-thickening liquids do the opposite. A property of non-Newtonian liquids is thixotropy where the liquid becomes thinner as it is being sheared. This time-dependent, thinning property of the liquid makes the mixing time critical, else the product will be off-specifications.
Degradation happens when the components become overly heated, creating unwanted chemical reactions. This is prevalent to batch type mixers since the chamber is a closed system. Mixing adds mechanical energy into the system creating friction between fluid molecules. This friction then becomes heat that can degrade the system.
This process involves converting fine powders into strong, dense agglomerates called granules. This is done by mixing the powdered components and a binding liquid, aided by agitation as provided by an impeller. This process is known as wet granulation. High shear mixers, compared to ordinary mixers, also provide the means to break down the powder into finer particles.
Wet granulation can be broken down into three processes: wetting, growth, and breakage. Wetting happens when the powder encounters the binder liquid. This forms large agglomerates or powder masses known as nuclei. These nuclei then collide with one another resulting in consolidation and growth. As this happens, the large agglomerates become denser. The resulting granules are not uniform in size which are then broken down by the mixer. Shearing and impact forces break the granules to its final particle size.
Aside from adding a liquid binder, dry powders can act also as a binder. This powder melts due to the increase in temperature from the mixing itself or through heaters. This solves problems from liquid binders such as clogging of pumps and nozzles due to high viscosity.
These types are designed to run at very high speeds aimed to produce a very fine particle size distribution. This causes dispersed solids and liquids to be homogenized faster into a continuous phase. The rotor is specially contoured to create high pumping capacity and shear intensity. Vortices are created both above and below the mixing head. These vortices draw the mixture into the mixing head which is then expelled radially through the stator slots. Also, the vortex is capable of drawing agglomerates floating on the surface.
Bottom entry high shear mixers are installed at the base or side of a container or tank and are used with a slow speed anchor stirrer or scraper units. The bottom entry high shear mixer provides high shear homogenization while the stirrer distributes the output throughout the vessel or container. The rotor stator is connected directly to the motor of the mixer by a shaft, which rapidly rotates the rotor and stator to draw in materials for mixing.
The high speed rotation of the rotor blades of a bottom entry high shear mixer produces powerful suction that draws in liquid and solid materials downward into the center of the workhead. The created centrifugal force pushes the materials toward the edge of the workhead where they are milled between the rotor and stator. The process creates highly intense hydraulic shearing forces as the material is forced through the stator and projected radially toward the sides of the mixing container at very high speeds. As the process progresses, new material is drawn into the workhead in order to continue the mixing cycle.
Equilibrium mixing is used in high shear mixing to determine the characteristics of the completed mixture. It is the point at which further mixing is not necessary and will not change the properties of the product regardless of any mixing or processing. Equilibrium is the goal of high shear mixing and the point at which mixing stops.
High-shear mixers mix ingredients that are immiscible and naturally do not mix. When a mixture consists of two or more types of liquids, the final solution is referred to as an emulsion. The combining of a solid and liquid is called a suspension while the dispersion of a gas in a liquid is called a lyosol, which includes micellar solutions and aqueous solutions of biopolymers. The amount of energy necessary for mixing determines whether the combination of solids, gases, and liquids is homogenized.
In order to create a standard mixture using a high shear mixer, equilibrium mixing is used to decide the point at which the reactants in a mixture will not change. In dispersions, equilibrium is determined by the size of the particles, while equilibrium for emulsions is droplet size. The amount of mixing that is necessary to reach equilibrium is based on the number of times materials have to pass through the high shear zone.
The decision as to whether a mixture has reached equilibrium is based on the point at which a mixture has achieved its target characteristics. The various parameters include a mixture’s viscosity, dispersed particle size, and granule density. Once equilibrium is achieved, any effort to mix materials beyond that point will be a waste of time and not change the mixture.
The concept of equilibrium is essential for high shear mixing and is used for scaling up the volume of a rotor stator mixing head since the configuration of the mixing head assists a high shear mixer in reaching equilibrium by a given time. With smaller scale mixing heads, equilibrium is reached much faster than with scaled-up full production units.
With high shear mixing, equilibrium is achieved in a given amount of time, which is somewhere between 5 to 10 passes through the rotor stator. Going beyond the 5 to 10 passes is a waste of effort, may damage the mixer, wastes energy, and increases wear and tear on the equipment.
High pressure homogenizers or mixers apply high pressure to a liquid to force it through a membrane or valve that has narrow slits. The process causes high shear, large pressure drop, and cavitation that homogenizes the sample. A high pressure homogenizer uses a combination of shearing, impact, and cavitation. The term high pressure homogenizer refers to any homogenizer that forces a liquid in order to reduce particle sizes.
A high pressure homogenizer consists of high-pressure tanks containing the materials to be mixed with the pressure in the tanks being between 15 bars to 40 bars. As the materials are forced into the valve or channel with narrow slits, high shear stress, pressure drop, and cavitation occur, all of which act together to homogenize the mixture.
Changing the pressure and power input changes the size of the droplets or particles.
Since high pressure homogenizers are a closed system, they are protected against the effects of microbes and external contaminants. Charging of the components is completed in separate containers further lessening the risk of product contamination.
High pressure homogenizers are able to achieve precision control for flexibility and repeatability, real time response to parameter changes and the charging of components through individual pumps. They can process high volumes of materials thoroughly, which makes them ideal for the dairy industry. With their forceful processing and ability to recycle the material steam, high pressure homogenizers are able to achieve very small, submicron particle sizes.
The use of high pressure homogenizers is restricted to high volume processing due to their high cost with units costing over $10,000. Since more than one pumping unit is necessary for efficient operation, high pressure homogenizers are very heavy and require a larger area. The multiple materials mixed in a high pressure homogenizer requires that it be cleaned after each cycle to avoid cross contamination.
High shear mixers are a critical part of many industrial processes due to their ability to perform a wide variety of mixing functions. Applications they can perform include reduction, dispersion, homogenization, deagglomeration, and wet milling, all of which are designed to enhance the quality of a product and provide production efficiency. With the improvement of technologies, high shear mixers are replacing traditional mixers that have propellers and turbines.
There is a wide range of high shear mixer applications under this category. High shear mixers used in the food industry can create emulsions, suspensions, powders, and granules. A popular application is the manufacture of sauces, dressings, and pastes. Most of the ingredients are composed of solid particles, and immiscible liquids such as oil and water.
Some ingredients are more difficult to process such as ketchups, mayonnaise, and doughs. These liquids and semi-solids have viscoelastic properties which require a minimum force before creating flow. This requires specialized rotor-stator mixing heads.
Like in the food industry, pharmaceuticals deal with different types of mixtures. Inline high shear mixers are used due to its closed system eliminating any intrusion of contaminants. All pharmaceutical products such as tablets, syrups, suspensions, injection solutions, ointments, gels, and creams go through a high shear mixer, all of which have varying viscosity and particle size.
Paints (latex) are known to be a non-Newtonian, thixotropic liquid. This makes paints difficult to process. Paint thins as it is being sheared, either by processing or by end-use. Mixing time for these fluids are carefully controlled to prevent over shearing.
Viscosity of inks (printer) is the opposite of paints. Inks are considered rheopectic. Rheopectic fluids thicken as it is being sheared, making the mixing process time dependent.
Applications under this category include combining resins and solvents for casting or injection molding, modifying oil viscosity, emulsifying waxes, asphalt production, and so forth.
The mixing process is the central focus of many industrial processes and applications, which has made high shear mixers an essential part of producing high quality products, efficiently. As with all forms of industrial equipment, selection of the right high shear mixer for an application requires careful study and research. Mixer manufacturers supply a wide array of literature that can serve as a guide to the purchasing process and offer sales assistance with highly trained and knowledgeable personnel.
The first consideration when purchasing a high shear mixer is the type of product. The types of products processed by a high shear mixer have a viscosity of 1 centipoise (CPS) to 10,000 cps, with one cps being the viscosity of water. CPS above 10,000 cps resist flow and are difficult to mix.
High shear mixers are capable of performing a variety of mixing applications, including particle size reduction, blending, gelling, dispersion, and emulsification. Prior choosing a high shear mixer, it is essential to know exactly what results are required by the product and what its consistency will be. Modern high shear mixers can adapt to the needs and requirements of any product and are exceptionally flexible.
Sizing refers to the daily production rate of an operation, which can vary from several hundred to several hundred thousand. The efficiency of a high shear mixer is determined by many factors and includes allowances for downtimes, length of mixing time, material supply, and transport of raw materials. This particular aspect of the process influences the number of mixers to purchase since high volume operations of hundreds of thousands of product require multiple mixers to meet company production goals.
Every manufacturer is aware of the upfront costs and the amortizations of the cost over time. Purchasing a highly efficient and reliable high shear mixer may be initially expensive but pay dividends due to limited downtime, efficient and reliable production, and high quality products. In the selection of a high shear mixer, it is difficult to determine the cost since some equipment can be several thousand dollars but be able to produce exceptionally high quality products, which should be the main focus of the purchasing process.
One of the most common factors in regard to modern manufacturing is customization. So many industries and producers are developing new, innovative, and unique products that require equipment that is outside the normal parameters of standard equipment. Such specialization can be expensive but be highly beneficial and productive. In order to develop the proper piece of equipment to meet a producer’s needs, it is essential that they work with the experts in the mixer industry to plan, engineer, and design a mixer that perfectly meets the needs of their product.
Agitators are equipment used in homogenizing media inside a tank. It works by rotating the impeller at its immersed end at a controlled speed or revolutions per minute (rpm). The work exerted by...
An emulsifier is an emulsion device used for colloidal dispersion of liquid droplets of immiscible liquids in the presence of an emulsifying agent. It enables the combining of non-soluble solutions or liquids...
A homogenizer is a type of mixing equipment used to create a uniform and consistent mixture. It works by breaking the components and evenly distributing them throughout the solution. The components are either immiscible, have varying sizes, or are in different phases from each other...
An industrial blender is a machine for large-scale production that consists of a large tank capable of mixing and blending batches of manufacturing materials to create a reaction between the materials. The many uses for industrial blenders are due to their capacity and...
A mill is a mechanical device that is often a structure, appliance, or machine that is used to break down solid materials into smaller pieces by cutting, grinding, or crushing them. Many industrial processes involve...
A tank mixer is a mixing device that blends several different ingredients in a single tank to make a single solution. It is a mixing process capable of mixing wettable powders, liquids, emulsifiable concentrates, and surfactants. They mix and blend...
A mixer is a complex and precise tool that is used in combining and mixing of substances and chemicals for manufacturing, production, and industrial use. There are many types of industrial mixers including...
A plastic tank is a large capacity liquid or granular storage unit that can be vertical, horizontal, below or above ground, as well as movable. They are designed to hold several gallons of a variety of substances for long periods without experiencing wear, weathering, or deterioration...
A plastic water tank is a large capacity container designed to store water for household, agricultural, irrigation, and industrial manufacturing use. There are various types of water tanks produced to meet the needs of specific applications, with...
Pressure tanks are vessels that are used to store, hold, and/or convey gasses, vapors and fluids at pressures greater than atmospheric pressure, also known as high pressures...
Pressure vessels are enclosed containers used to hold liquids, vapors, and gases at a pressure significantly higher or lower than the ambient pressure. They are widely used in various industries such as...
Stainless steel tanks are widely used in food, beverage, dairy, medicine, cosmetics, and other manufacturing processes where cleanliness and purity are important. These are also used in industrial plants for storing chemicals and gases where strong resistance from chemical degradation is required...