Types of Agitators

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 mechanical mixing of low to medium viscosity fluids. These type of propellers are also called as 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 speed and are much larger than propellers. Turbine has an excellent feature in designing the flow patter 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. Radial design make the fluid to flow at high velocity in radial direction where as axial impellers use pitched blades, make the fluid to flow parallel to shaft in downward direction and then push the fluid towards the wall of the agitator vessel. For gas dispersion operation radial turbine impeller is used and axial turbine impeller is used for chemical reactions, suspension solid and miscible liquid mixing. 

Download Calculation Sheet : Agitator Power Requirement and Mixing Intensity in agitator mixer

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 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 revolution 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 high viscous materials	Not suitable for miscibility operations
Helical Ribbon type Helical screw	Polymer and paints 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 for 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 gear box
Propeller	Dairy and food processing Chemicals processing	Less  Metzner –Ott shear rate constant Homogenization Good miscibility	Motion of liquid starts on one spot Dead spots formation at high rotation speeds Occurrence of solids settling at low speeds