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What Are High Shear Mixers?

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  • Written By: Paul Scott
  • Edited By: E. E. Hubbard
  • Last Modified Date: 23 June 2014
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    Conjecture Corporation
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High shear mixers are devices designed to completely combine fluid, gaseous, and solid components that would normally not mix completely using conventional methods. These devices make use of a fluid dynamics phenomenon known as shear strain to combine difficult-to-mix materials. Shear strain occurs where two fluid bodies move across one another at different speeds creating an area of deformation along the contact area between them. High shear mixers use a series of high-speed impellers rotating within a stationary housing to effectively mix one component material introduced into a constant flow of another at differing speeds. There are several types of shear mixers commonly used, including batch, inline, and ultra-high shear mixers.

Material combinations that, under normal conditions, do not mix completely are known as immiscible mixtures. Oil and water are a good example of such a generally incompatible pair of elements. Thoroughly combining normally incompatible combinations of fluids, solids, and gases is, however, a necessary part of many industrial and chemical processes. Where normal combination methods fail, high shear mixers are employed to achieve a complete mix of otherwise immiscible components. These mixers harness a fluid dynamics mechanism known as shear stress that occurs at the area where two bodies of material moving at differing speeds contact one another.

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Shear stress causes localized deformation of the two material flows that serves to vigorously combine them along the shear plane. In high shear mixing machines, this effect is generally achieved with a high-speed impeller or rotor that rotates within a close-fitting static housing, or stator. Component materials introduced into the chamber created by the stator will experience higher rotational velocities at its outer edge than those at its center. This speed differential causes the shear stress necessary to effectively combine the materials. These combinations may consist of different fluids, fluid-and-gas, or fluid-and-solids pairings, the resultant mixtures of which are known as emulsions, lysols, and suspensions, respectively.

Several different types of high shear mixers are commonly encountered in the food processing, pharmaceutical, cosmetics, and paper-producing industries. These include batch, inline, and ultra-high shear mixers, each with specific operational benefits. Batch mixers feature a mixing tank with the impeller located in its bottom with component materials being loaded into the tank from the top, allowing this type of mixer to rapidly process large volumes. Inline mixers are particularly suited to mixing fluid/powder combinations and feature a linear feed/discharge arrangement that draws the mixture through it as well as mixing the materials. Ultra-high shear mixers generally allow for single pass mixing and have a series of perforations in the stator through which the materials are forced at high speed.

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