Agitators
An agitator is a type of mixer that deals with low-viscosity substances in low-shear applications. They can range in size from small agitators used in laboratories to large agitators used in industrial settings that are capable of holding up to 10,000 gallons. Their primary functions are ensuring substance uniformity and producing flow within a vessel. Therefore, the functions of agitators are secondary, and they serve as an aid to the mixing process.
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Applications of Agitators
Agitators can be found in applications such as the creation of household, commercial, and industrial products like liquid detergents and heating compounds. Common substances that agitators are used for include grease lubricants, adhesives, varnishes, inks, and paints.
Design and Function of Agitators
The process of agitation differs from mixing, in that agitation involves the designed and specific movement of a liquid, while in mixing, the movement is random and non-specific. Agitation keeps an already mixed solution in a state that is necessary for the final product. The component that powers an agitator is known as the impeller. The impeller is the component that adds force to the material being mixed. Examples of impellers include paddles, anchors, gates, turbines, propellers, and the blade located in the center of a washing machine.
Impellers fall under two categories: axial flow impellers, and radial flow impellers. Radial flow impellers apply a horizontal flow to the mixing process and are typically selected for elongated vessels and low-level mixing processes. Unlike their axial counterparts, radial flow impellers do not have a high turnover flow. Axial flow impellers implement an axial (up and down) flow pattern.
Common examples of axial impellers include:
Hydrofoils
This impeller works with liquids of viscosities up to 3,000 cps. One advantage of this type of impeller is the implementation of laminar flow – or the movement of the fluid particles in parallel layers – in order to reduce turbulence.
Pitch Blade
The most versatile of impellers, and are ideal for blending two or more liquids, and are capable of mixing liquids with viscosities up to 50,000 cps.
Marine-type propellers are often used on marine vessels. Benefits include cost and energy efficiency. However, they are not recommended for larger applications due to their price and weight. Marine-type propellers are ideal for mixing liquids with viscosities up to 5,000 cps.
For high-viscosity products such as polymers, adhesives, and grease lubricants, mixers with multiple agitators are used. These mixers contain several agitators that operate independently from one another and a flexible control system that allows for it to switch gears. This control system enables the machine and its operator to work with a fast-changing multitude of products, making it a recommended machine for companies that require a fast turnover time for products of different materials.
Benefits of Using Agitators
Technological advances are constantly being made in developing new mixing machines. The primary focus of this research has been toward the heat transfer, controls, power, and liquid induction and the overall design of the agitator. The newer designs of mixers allow for up to three different agitators to operate within one vessel during the processes of charging, mixing, and discharging the vessel’s ingredients. Each agitator can be independently powered and controlled by an electronic variable-speed drive. When a third agitator is added, the mixer’s functionality greatly increases. Two challenges that are commonly found in mixing are stratification (separation of liquids that are incapable of being mixed) and solid suspension (state of a solid of which its particles are capable of separation). Fortunately, the velocity of the mixer can be calculated in order to achieve the desired level of mixing.
Factors to Consider When Purchasing Agitators
Agitators are primarily used in liquids, as they do not work well with thicker, more viscous materials. Agitators in food mixing and industrial products can have similar configurations. Alternatively, they are available as removable rods that can be placed in a substance long enough to agitate it. Agitators can be used in conjunction with other mixing devices within a vessel. Outside of maintaining consistency, promoting heat transfer and producing flow, agitators do not have as much of a practical use. A variety of agitators are available, such as paddle agitators, gate agitators, anchor agitators, radial propeller agitators, propeller agitators, turbine agitators, and helical agitators. All of these types have their own advantages and disadvantages. For instance, some types require more power, and others work well with only certain types of substances. Therefore, it is important to take into consideration gravity, viscosity, and properties of the desired material, as well as the application for which the agitator will be used.
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