Types of Agitators

Propeller agitators are commonly made of three-bladed attached to the main shaft. They are flexible in operations and mostly used in the mechanical mixing of low to medium-viscosity fluids. These types of propellers are also called marine-type propellers. The diameter of the propellers depends on the rotational speed and diameter of the batch reactor or the agitator vessel. Depending on the agitator vessel size and the fluid viscosity the power consumption of the propeller agitator may exceed more than 50kW.                         

Turbine impellers operate at low speeds and are much larger than propellers. The turbine has an excellent feature in designing the flow pattern where a change in design can divert the flow pattern of fluid by radial flow or axial flow in the reactor vessel. Based on the configuration of the impeller blades these flow patterns can be achieved. The radial design makes the fluid flow at high velocity in the radial direction whereas axial impellers use pitched blades, make the fluid flow parallel to the shaft in the downward direction and then push the fluid towards the wall of the agitator vessel. For gas dispersion operation radial turbine impeller is used and an axial turbine impeller is used for chemical reactions, suspension solid and miscible liquid mixing. 

Types of agitators models, application and comparison:

Agitator models	Application	Advantages	Disadvantages
Paddle: Flat paddles Finger paddles Gate paddles	Solid mixing Slurry mixing	Heavy duty mixing Adjustable to 2 or 4 blades Excellent for low-speed	High power consumption Inefficient liquid circulation
Counter-rotating paddles	Paste mixing	Efficient in the laminar condition Blending	Vibrates at high speed Not suitable for liquid mixing
Tumbling	Blending	Paste and viscous material mixing	Not suitable for  fluid solutions
Disk and cone	Polymers and dispersion preparation	Viscous solution mixing with 60 revolutions per second	Paste mass cannot be handled
Free shaft suspension	Sugar processing	Suspension, Thickening operation	High power requirement
Impeller type	Emulsion preparations	Good temperature control Creates axial flow Good phase mixing	Not for viscous materials
Turbine agitator Straight blade Pitched blade Vaned disk Curved blade	Liquid and gas reactions	Excellent for dispersion operations Creates good radial flow	Only for less viscous liquid below 15 to 20 Ns/m2
Slotted rotary Rotating disk	Powders and cosmetics	Unique particle size and homogeny product formation	Minimum axial flow Operates better only for 0.1 to 0.01mm particle size solids
Screw Screw in cone	Food and snack processing	Homogenization of highly viscous materials	Not suitable for miscibility operations
Helical Ribbon type Helical screw	Polymer and paint processing	Handles viscoelastic liquids that are more than 20 Ns/m2	Less radial flow patterns
Gate	Blending operations	Good speed control Handles pseudoplastic liquids	Not suitable for gas-to-liquid operations
Anchor Round anchor Combine anchor and gate	Milk and fat processing	Efficient heat exchange between the reactor walls and reaction mass (fluids)	High power consumption Requires heavy-duty gearbox
Propeller	Dairy and food processing Chemicals processing	Less  Metzner –Ott shear rate constant Homogenization Good miscibility	The motion of liquid starts on one spot Dead spots formation at high rotation speeds The occurrence of solids settling at low speeds