Agitators and their classification

The agitator is the stirring blade (or impeller), which is one of the important components of the stirring device. In the structural optimization design of mixing equipment and the design and development of new agitators, the design of the agitator is the most important thing, and it is also very important for the selection of the agitator. Choosing different stirring blades will play different roles in the physical and chemical reaction processes such as the flow of the fluid inside the stirring container, the mass transfer between the fluids, and the heat transfer. Agitators are classified according to different standards, roughly divided into the following groups:

(1) According to the shape and structure of the agitator blades , it can be roughly divided into turbine agitator, anchor agitator, paddle agitator, ribbon agitator and propeller agitator. Among these commonly used paddle structures, the paddle agitator is widely used. There are mainly two types of paddle structures: oblique blade and flat blade, while the ribbon type blade is a helical surface structure.

The following is a brief introduction to agitators with different paddle structures.

① Propeller agitator . The agitator is generally composed of 2 to 3 propulsion propeller blades, and usually operates at a relatively high speed. When the propeller agitator is working, it mainly produces axial liquid flow and has a large circulation volume, which is more suitable for mixing and stirring low-viscosity liquids, emulsions and other fluids. When designing a propeller stirrer, in addition to the usual installation method, the stirring shaft of the stirrer can also be installed horizontally or obliquely in the stirring tank. In this case, the fluid circulation circuit in the stirring container is asymmetrical. , which can increase turbulence and prevent the occurrence .

② Turbine agitator . Typically, a turbine agitator consists of 2 to 4 straight or curved blades mounted on a horizontal disc. The ratio of the outer diameter of the paddle, the width of the paddle and the height of the paddle is generally 20:5:4. Since the turbine agitator will produce radial flow under high turbulence when the stirring work occurs, this type of agitator is generally used for the dispersion of gas and immiscible liquid and the liquid-liquid phase reaction process.

③ Paddle agitator . In most cases, paddle agitators are divided into two types: flat paddle agitator and oblique paddle agitator.

The simple structure of the flat paddle agitator is generally composed of two straight paddles. The ratio of the diameter of the paddle to the height of the paddle is generally 4:10, and the radial flow velocity generated during stirring is relatively small. The structure of a simple oblique paddle agitator is composed of two blades turned oppositely by 45° or 60°, so generally an axial liquid flow will be generated. The paddle agitator has a simple structure and is usually used for mixing low-viscosity liquids and dissolving and suspending solid particles.

④ Anchor mixer . The shape of the outer edge of the paddle of the anchor stirrer should be consistent with the inner wall of the stirring vessel, and there is only a small gap between the two. Due to this structural feature, the anchor stirrer can be attached to the inner wall of the stirring vessel The viscous reaction products on the surface or the solid phase particles deposited on the bottom of the tank are removed, and a better heat transfer effect can be ensured. Anchor stirrer - generally used to stir high viscosity Newtonian fluid.

⑤ Ribbon mixer . The outer diameter of the ribbon of the ribbon stirrer is equal to the screw pitch. The stirrer of this structure is specially used for stirring and mixing of high-viscosity liquids and pseudoplastic fluids, and is usually operated in a laminar flow state.

(2) According to the use of the agitator , the agitator can be divided into two types: high viscosity agitator and low viscosity agitator according to the viscosity of the stirring medium in the container . For agitators used for high-viscosity fluids, the more common ones are frame type , propeller type, ribbon type, sawtooth disc type, anchor type, etc., while for low-viscosity fluid agitators, the common ones are Brumakin Type, propulsion type, open turbine type, disc turbine type, three-blade backward curved type, paddle type, plate frame paddle type, etc.

(3) According to the flow pattern generated by the agitator during the stirring process , it can be classified into two types: axial flow agitator and radial flow agitator. The most common types of radial flow agitators are straight blade agitators and curved blade turbine agitators . The fluid in the stirring container will generate radial flow under the agitation action of the paddle, thus colliding to generate two cycles of upward and downward respectively, and finally the fluid returns to the paddle after the flow.