Types of agitators

Types of agitators

1. Types Of Agitators

2. Outline: Introduction Types Of Agitators Selection Criteria For Agitators Power required For Agitation

3. Agitator: An agitator is something which is used to stir liquid or mixture of liquids. It can be used in various operations, in a pharma industry it can be used in multiple operations like reactions, drying, filtration, etc.   Agitation is the process of keeping a mixture that has been mixed in the proper mixed state required for the 'end' product. Introduction:

4. Types of Agitators Paddle Agitators Anchor Agitators Radial Propeller Agitators Propeller Agitators Turbine Agitators Helical Agitators

5. (1) Paddle Agitators: This is one of the most primary types of agitators with blades that reach up to the tank walls. Paddle agitators are used where an uniform laminar flow of liquids is desired. (2) Anchor Agitators:   This simple agitator consists of a shaft and an anchor type propeller and can be mounted centrally or at an angle. It is mainly used in reactors.

6. (3) Radial Propeller Agitators:   Radial agitators consist of propellers that are similar to marine propellers. They consist of two to four blades that move in a screw like motion, propelling the material to be agitated parallel to the shaft. (4) Propeller Agitators:  A propeller agitator is shaped with blades tapering towards the shaft to minimize centrifugal force and produce maximum axial flow. Propeller agitators are popular for simple mixing jobs. (5) Turbine Agitators:   Yet another type of process agitator is the turbine agitator. Turbine agitators can create a turbulent movement of the fluids due to the combination of centrifugal and rotational motion.

7. (6) Helical Agitators:   These agitators have blades with a twisted mechanism, just like the threads of a screw. The curves result in a vigorous motion of the fluids to be agitated. Helical agitators are most useful for mixing viscous liquids. 

8. Agitator Type Applications Advantages Disadvantages Paddle * Mixing of Solids, * Slurry Mixing, * Heavy duty, * Apt for Slow operation, * Can have 2 or 4 blades * Power Consumption is very high , * Inefficient Mixing Turbine * Liquids and Gas reactions, * Highly used during Reaction and Extraction Operations. * Generates high  Radial Flow, * Highly used for  dispersion operations * Not preferred for solvents with high  viscosity Screw type * Have to use in addition  to other agitators . * Mostly used in Food processing. * Uniform mixing of High viscous masses. * Not preferred for im -miscible solvents. A simplified brief description has been tabulated below:

9. Agitator Type Applications Advantages Disadvantages Helical Blade *Ribbon Type *Helical Screw * Most Probably used in Paint industry. * Can handle Visco -elastic liquids efficiently * Low possibility for Radial mixing Anchor * Highly used in Pharma Industry for Several Operations * Increase possible heat  transfer rate in reactors, from reactor heat transfer surface  to Mass. * Required high Efficiency Gear box, * Required high Power. Gate * Highly used for blending Operations * Provides efficient Mixing and agitation control , * Not preferred when both liquids and gases combine involves  Propeller * Suitable for GLR's, ANFD's, can handle Corrosive materials with Glass lining. * Will increase the homogeneity. * Need to be operated at high speed to avoid solid settlings in reactors.

10. Selection Criteria For Agitators: There is not necessarily any direct relation between power consumed and amount or degree of mixing. mainly depends on the viscosity of fluid. When the mixing time is critical, the best mixer is the one that mixes in the required time with the smallest amount of power. For mixing reagent in a feed tank or blending product from different batches in a storage tank, a relatively small size mixer might be used, even if several minutes are required for complete mixing.

11. POWER REQUIRED FOR AGITATION: The power consumed by a mixing impeller can be studied by experimentation guided by dimensional analysis.Considering diameter of mixer, D as the basis , the power, P consumed by the mixer is a function of: P= f(N,D,gc , μ ,g, ρ ) ------------------ (1 ) By taking account of the shape factors eq. (1) can be written as N p = f( Re, Fr, S1, S2……… Sn ) ------------------ (2) Using dimensional analysis ------------------ (3 )

12. Where, S1 = , S 2 = , etc,. The three dimensionless group are: Npo = Power no. = Nre = Reynoldys no. = Nfr = Froude no. = Where, P = Power consumption, kW ρ = Fluid density, kg/m3 μ = Fluid viscosity, Nsec /m2

13. N = Agitator speed, sec-1 D = Agitator diameter, m g = Gravitational acceleration, m/sec2 gc = Newton’s low proportionality factor The froude no. is significant only when wave motion or vortexing on the surface of the liquid takes place and only when NRe > 300. For baffled tanks or for side entering propellers or for NRe <300, f roude no. is insignificant . For unbaffled tank : Eq . (3) can also be written as : = φ = f ( Nre , S1, S2……… Sn ). m=

14. Where φ = Power function m = Exponent a,b = Constant depends on the type of mixer . For NRe >300 6 Blade turbine a = 1, b = 40.0 3 Blade propellers a = 1.7, b = 18.0 For Ex,. If we increase rpm and viscosity of fluid by 2 times then, the power required is increased by 8 times.

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