We offer complete Process solutions for all type of agitator with correspondenceTanks.
What are agitators? Agitators are devices that are used to stir or mix fluids, especially liquids, which is one of the basic mechanical process engineering operations. Essentially, agitators are used for the homogenization of liquids or liquid-solid mixtures by generating horizontal and vertical flows. These flows are generated by rotating agitator blades.
The Agitator Process
A rotating agitator generates high speed streams of liquid which in turn entrain stagnant or slower moving regions of liquid resulting in uniform mixing by momentum transfer. When it is necessary to mix materials of different densities, it is better to use vertical flow agitators because of the tendency of sedimentation of the denser component. Wherever possible, movement of the entire amount of material together in the mixing vessel, which occurs frequently during the agitation process, should be avoided because of the unwanted separation caused by centrifugal forces.
At the simplest level, agitators consist of an impeller and a shaft. An impeller is a rotor inside a tube or conduit attached to the shaft. It is used to increase the pressure and flow of a fluid. Modern agitators use sophisticated process control electronic devices to regulate the mixing process.
Principles of Process Agitators
The Science behind Process Agitators
Technically speaking, for a liquid mixed in a tank with a rotating agitator, the shear rate is greatest in the immediate vicinity of the agitator. The shear rate decreases exponentially with distance from the agitator. Thus the shear stresses and strain rates vary greatly throughout an agitated liquid in a tank. As the viscosity of the fluids to be mixed increases, the physics fluid mechanics change from that of turbulent flow (like in liquid agitators) to that in which viscous drag forces dominate. Additionally, some fluids exhibit Non-Newtonian behavior – their viscosity cannot be designated by a single coefficient. Mixing of such fluids requires special heavy duty agitators. As the dynamic viscosity of a Newtonian liquid is independent of shear at a given temperature, its viscosity will be the same at all points in the tank. In contrast the apparent viscosity of a non-Newtonian liquid varies throughout the tank. This in turn significantly influences the mixing process. For shear thinning liquids, the apparent viscosity is at a minimum in the immediate vicinity of the agitator. The progressive increase in the apparent viscosity of a shear thinning liquid with distance away from the agitator tends to dampen eddy currents in the mixing tank. In contrast, for shear thickening liquids, the apparent viscosity is at a maximum in the immediate vicinity of the agitator. In general shear thinning and shear thickening liquids should be mixed using high and low speed agitators respectively.
Fluid Movement in Process Agitators
Wherever possible, the movement of the entire contents of the agitator vessel should be avoided as rapid movement tends to segregate the components due to centrifugal forces.
The mixing time is short if the components to be mixed undergo a large number of changes of location. This can take the form of movement of the agitator itself or of material flows generated by the agitator. They can be achieved by impact, flow around obstacles, crossing directions of flow and speed differentials at the interfaces of parallel flows
The purpose of mixing impellers is to transfer the energy provided by the motor to the product in the most efficient way in order to produce the desired effect in the least amount of time. Also called agitator blades, each mixing impeller type converts the energy given to it in a different way. A hydrofoil converts most of the energy into motion of the product and very little into shear. A three bladed propeller will convert more of the energy into shear than the hydrofoil but still mostly produces motion. The axial flow turbines and radial flow turbines devote a higher ratio to shear and a dispersion blade is almost completely devoted to shear production. Mechanical considerations may also affect the agitator blade selection as in the case of a folding impeller being utilized to fit into a tank through a small aperture
Types of Impellers
- 1. Hydrofoil Impellers
- 2. Propellers
- 3. Right Hand Propellers
- 4. Steep Pitch Propellers
- 1. Folding Impellers
- 2. Axial Flow Turbine RBW (Reduced blade width)
- 3. Axial Flow Turbine
- 4. Radial Flow Turbine
- 1. High flow dispersion
- 2. Dispersion blade
- 3. Ultra shear dispersion blade
Agitators are typically used in…
- – Chemical Industry : Uniform mixing of various raw materials suspension, reaction, melting, promotion of heat transfer,disperstion, various chemical plants etc like (soap, paint etc)
- – Food Industry : high precision mixing of raw food materials, suspension melting , heat transfer etc. (Preparation of cake mix, spices, and flavors, sugar, alcohol, tempura coating etc)
- – Oil and gas Industry : blending, gas absorption, reaction, extraction, suspension of sludge etc (petrol, gasoline refining etc)
- – Water Treatment : waste water treatment, aeration ,chemical adjustment, waste liquid treatment etc
- – Coal Industry : Slurification,COM Adjustment, prevention of COM Precipitation, gasification adjustment tanks etc
- – Textile Industry : High viscosity polymer mixing, melting of dye, mixing of glue materials etc
- – Rubber Industry : suspension polymerization, extracting, melting of rubber etc
- – Paper Industry : uniform mixing of chest and black liquor etc
- – Fermenting Industry : Aeration, promotion of fermentation, mixing of solutions etc
- – Fat Industry : heating, mixing, extraction, reaction, storage etc
- – Prevention of Air Pollution : Exhaust gas desulphurization (Plaster slurry tank etc)
- – Paint Industry : Agitators are used to mix liquid-liquid and liquid-solid raw material properly
- – Pharmaceutical Industry : Blending of active ingredients of a formulation