Turbine mixers

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A turbine mixer is a mechanical device which is used in the mixing of the different types of liquids by using different types of blades and impellers.

A turbine mixer is an impeller with essentially consists of contant blade angles with respect to the verticle plane, over its entire length or ove finite sections having blades either verticle or a set of an angle less than 90 with the verticle.

Blades may be either curved or flat.

Turbine mixer

CONSTRUCTION

A turbine mixer may be used for more viscous fluids and a typical construction.

The impeller has four flat blades surrounded by perforated inner and outer diffuser rings. The

rotating impeller draws the liquid into the mixer 'head' and forces the liquid through the perforations with considerable radial velocity, sufficient to overcome the viscous drag of the bulk of the fluid.

One drawback is the absence of an axial component, but a different head with the perforations

pointing upwards can be fitted if this is desired.

As the liquid is forced through the small orifices of the diffuser rings at high velocity large shear

forces are produced. When mixing immiscible liquids, if the orifices are sufficiently small and velocity sufficiently high, the shear forces produced enable the generation of droplets of the dispersed phase which are small enough to produce stable dispersions

(water-in-oil or oil-in-water). Turbine mixers of this type are therefore often fitted to vessels used for the large-scale production of emulsions and creams.

Turbine-type mixes will not scope with liquids of very high viscosity, as the material will not be drawn into the mixer head. These liquids are best treated as semisolids and handled in the same equipment as used for such materials.

Characteristics

  • Rapiad blending of thin materials from 1000 to 10000 gal
  • Intensive dispersion typeagitation upto 1000 gal.
  • Average multi liquid phase reactions upto 30000gal.
  • Slurries upto 60% solids.
  • Solids to particle size of 10 mesh.
  • Liquids to the viscosity of 7000000 cps
  • Figrous slurries upto 5%.

PRINCIPLE

The turbine mixer mainly works on the principle of shearing action or force.

WORKING

Turbine mixer operation mianalogous to that of a centrifugal pump working in a vessel against negligible back pressure.

The mixing action is accomplished bythe turbine blades which contrain and discharge the liquid.

The radial flow from the impeller impinges on to the vessel walls, where it splits in to two streams. These streams cause mixing in there energy.

When the turbine mixers are operated at sufficiently high rotational speeds both the radial and tangential flow becomes pronounced along with the vortex formation.

This flow of suitation warrants the installation of baffles into the vessels for the mixing process for the uniform mixing.

The different types of blades used in this mixers are

  • Flat blades
  • Disk type flat blades
  • Pitched blades
  • Curved blades
  • Tilted blades
  • Arrow head blades
  • Pitched curved blades etc

PHARMACEUTICAL APPLICATIONS

  • The propeller mixer used in mixing the liquids upto 2000cp
  • It has the capacity to mix low visocity emulsions
  • Liquid phase chemical reaction
  • Used in mixing of suspensions with particles size upto 0.1 to 0.5 mm maximum with a drying residue of 10%
  • Mainly used for semisolid materials.
  • It is used for mixing of more viscous liquids. Eg: Syrups, liquid paraffin, glycerine etc.

ADVANTAGES

  • Fine mixing.
  • Used for making true solutions

DISADVANTAGES

  • High cost
  • Sensitvity in operation of vessel geomentry and in location within the tank.
  • Not used for rapid settling suspensions.
  • Not used for high viscosity liquids.

REFERENCE

  1. Mehta RM, Pharmaceutics-I: Mixing and Homogenisation (1996), Page no:114.
  2. Badger, Intro To Chem Engg, 2001.

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

Comments

A.R.Khan's picture

Do you know any commericial pharnmaceutical products manufactured using Turbine Mixers ?

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