Agitator and mixer are mechanical device which is used for mixing, blending the process fluid like liquids, gases and Solids. Agitator use in tanks, reactors Vessels for
- To produce static or dynamic uniformity in multi component multi phase systems. E.g. Blending of liquids.
- To facilitate mass or energy transfer between parts of a system not in equilibrium.
- To promote phase change in a multi component system with or without change in composition. E.g. Homogenization, gas dispersion and crystallization.
Impeller of agitators
An impeller converts the input energy to fluid flow and head (velocity or shear).Based on the predominant flow pattern, impellers are classified as follows.
Types of agitator
Mechanical agitators are divided into six basic groups depending upon their design and application.
- Paddle agitator
- Propeller agitator
- Radial propeller agitator
- Turbine agitator
- Helical agitator
- Anchor agitator
This type of agitator use for where uniform laminar flow of services required. These types of agitator simply push the inside liquid cause that create laminar flow but not any radial flow. And the circulation and mixing are poor as compare to other type. The RPM of this type of agitator is very less approx. 80 to 150 RPM. interview question
Propeller type agitator uses for simple application in reactor for mixing, blending, suspending, and dispersing application. It is uses with tapering type blade due to the tapering blade reduce the buildup of centrifugal force and increase the axial flow. The propeller blades diameter is around 15 to 35% of the tank or vessel diameter and the RPM is approx. 300 to 500 RPM. It is some time close couple with electrical motors. Practically it is very expensive for simple mixing process in small tanks.
Radial propeller agitator
In the radial type agitator blades are fixed at bottom of the agitator and these blades are create the shear and turbulence flow but the turbulence and shear are controlled by varying the its height, width and angle of blade pitch. The blades are pitched to the direction of rotation.
Turbine agitator is use in reactors for effective mixing, blending and suspending applications. Turbine type of agitator creates turbulence flow of the fluid because of the centrifugal and rotary motion. There are many types of blades are use in the turbine type of agitator these are mentioned below flat blade, disk flat blade, curved type blades, pitched type blades. It is use for homogeneous mixing, good heat transfer, and high blending capacity. Radial type blade agitator gives high discharge velocity but consume more power. Pitched blades give radial and axial flow of the liquids but radial flow is more than axial flow. The diameter of the blade is kept between 1/3 to 1/6 of the tank’s diameters. For the general rule for higher viscosity fluid take higher blade angles.
Helical screw type
In the helical screw type agitator instead of the blade, screw is use. The screw is fixed in shaft from bottom of the tank to liquid surface. Baffles are use in tanks for create turbulence flow. Use for very high viscous fluids. The main function of this type of agitator is that to increase the contact between reactive product and increase the heat transfer coefficient.
This type of agitator has very close clearance between blade and shaft. The diameter of the blade is between 90 to 95 % of the tank diameter. It is use for very less viscous fluid between 5000 to 50000 cp. This is mostly use in crystallization reactor where cooling jacket is necessary along with good mixing.