High Shear Mixer: What Is It? How Does It Work? Types Of

High-Shear Mixers also known as high-shear reactors or rotor-stator mixers distribute, or carry, one phase or ingredient whether it is liquid, solid, or gas into a main continuous phase i.e. liquid so that it would normally be immiscible.

High-Shear Mixers are used to dissolve, emulsify, homogenize, and grind immiscible mixtures with constituents of the same or different phases that are too difficult and time-consuming to be processed by ordinary mixers.

Working Principle:

Fluids undergo a shearing process when the surface area of one liquid moves against the motion of the surface area of another liquid. A high-shear mixer uses a rotating blade or high-speed rotor, usually powered by an electric motor, to "work" the fluid, creating flow and shear. The tip velocity, of the fluid at the outside diameter of the rotor is higher than the velocity at the center of the rotor, thus creating the velocity difference which creates shear.

A stationary constituent is used in combination with the rotor which is referred to as the stator. A high-shear zone is formed between the stator and rotor when the material exits from the rotor. The rotor and stator combined together are often referred to as the mixing head called a generator. A large high-shear rotor-stator mixer contains a number of generators.

Crucial factors include the diameter and rotational speed of the rotor, the distance between the rotor and the stator, the time in the mixer, and the number of generators in the series.

Adjustable factors include the number of rows of teeth, their angle, and the width of the openings between teeth.

Types of High Shear Mixers

High Shear Mixers are classified into many types according to their configuration. All these types perform different mixture processes according to their degree of efficiency. Basically, mixer configurations depend upon the applications i.e. for what purpose we need these mixers.

• Batch High Shear Mixers

This type of high shear-mixer mixes all the constituents by series in large volumes in a vessel. Charging of these constituents is usually done at the top of the vessel. Hindu Batch high shear mixers can also be built as one mixing head that can lift several vessels. This type of mixing is faster than in-line high shear mixers with the same power rating.

One problem in this system is the cleaning process between batches and is particularly noticeable in viscous mixtures as residues from the previous batch can become a contaminant to the next batch. Clean in place systems are employed to overcome this problem.

• In-line High Shear Mixers

This type of high-shear mixer involves mixing the constituents in a cell with an inlet and an outlet. In contrast to the batch-type mixer, it creates centrifugal force which acts as a pump to drive the mixture through the cell which is always closed which makes it less prone to contamination. Inline mixers are more controlled than batch mixers as it is a part of the product stream. The product flowing from the mixer can be monitored continuously which enables the process operators to modify parameters in real-time. It serves as the application for mixing, emulsifying, homogenizing, disintegrating, dissolving, blending, particle size reduction and de-agglomerating.

• Powder Induction High Shear Mixers

This type of high shear mixer uses a vacuum system to draw powdered constituents into the mixing head directly and this vacuum is generated on the rotor-stator assembly which draws the powder from a hopper. This solves several problems that arise when dealing with the processing of powders.

Some powders quickly agglomerate upon contact with the liquid when charged into the mixing cell. Clumps tend to form on the surface of the liquid which will then require a higher mixing speed to form a spiral which is required to draw the powders to the mixing head. To attenuate this, these powdered constituents need to be added carefully and slowly to prevent the formation of lumps on the surface. However, adding too slowly can cause the undissolved and floating particles on the surface which has a direct impact on the production hence in profit margins in mass production.

Sometimes over shearing makes the mixture either thinner or thicker than the desired viscosity i.e. viscosity can change when under force to either more liquid or more solid like in non-Newtonian liquids. And also sometimes degradation happens, creating unwanted chemical reactions when the constituents become overly heated.

• High Shear Granulators

High-Shear Granulators convert fine powders into dense agglomerates called granules which are carried out by mixing the powdered constituents and a binding liquid, aided by agitation as provided by an impeller. This process is known as wet granulation. High shear mixers also provide the means to break down the powder into finer particles in spite of other mixers.

This process of wet granulation can be broken down into three processes: wetting, growth, and breakage. Wetting happens when the powder comes up against the binder liquid forming large agglomerates known as nuclei which then collide with one another resulting in consolidation, thus making the large lumps become denser. These resulting agglomerates are non-uniform which are then broken down by the mixer to get the final particle size.

• Ultra-High Shear Mixers

Ultra High-Shear Mixers are designed to run at very high speed aiming to produce a very fine particle size distribution that makes dispersed solids and liquids to be dissolved faster into a continuous phase. In this type of high-shear mixer, the rotor is specially designed to create high pumping capacity and shear intensity. Spirals are created both above and below the mixing head to draw the mixture into the mixing head which is then expelled radially through the stator slots. Also, these spirals are capable of drawing agglomerates floating on the surface.

Hindu Engineers specialises in custom designed state of the art high shear batch mixers. Hindu Engineers are High Shear Mixer Manufacturers, Suppliers in India.