Turbine mixer is a type of process agitator. They are used as an alternative to propellers for mixing low viscosity liquids and typically for the effective mixing of medium viscosity liquids. The velocity of mixing using turbine systems is low compared to propellers.
Principle of Turbine Mixer
Turbine mixer agitators
can create a turbulent movement of the fluids due to the combination of
centrifugal and rotational motion. These combined motions cause effective
mixing of low to medium viscosity fluids.
Construction of Turbine Mixer
A turbine consists of a
circular disc to which several short blades are attached. Compared to
propellers the diameter of turbines is approximately 0.13-0.67 to that of the
diameter of the vessel, with 0.33:1 being the most typical. There is a wide
range of turbine designs, Fig.1. The blades may be straight, pitched, curved,
or disk type. The turbine rotates at lower speeds usually 50 – 200 r.p.m. than
the propellers. Flat blade turbines produce radial and tangential flow but as
the speed increases radial flow dominates. A pitched blade turbine produces
axial flow. Near the impeller zone of rapid currents, high turbulence and
intense shear are observed. Shear produced by turbines can be further enhanced
using a diffuser ring. The diffuser ring is a stationary perforated ring that
surrounds the turbine.
Working of Turbine Mixer
A mixer is filled through
with an opening at its top. Usually, it is a pan or drum within which mixing
blades revolve about the vertical axis. The variable speed drill with the turbine
mixer whip air into the material mixture. The air in the mixture yield bubbles
contributing to mixing. The top entry turbine mixer is fitted with various
impellers and turbines to suit heat and mass transfer in solids, suspensions,
and liquids. This type of mixer does not damage the product. Top entry high
shear causes uniform emulsification and homogenization. The mixing blades
revolve around the vertical axis.
Fig.1: Types of Turbine Design
Advantages of Turbine Mixer
- Turbines are used in emulsification as they generate higher shearing forces than propellers even at low pumping rates.
- They are effective in mixing high viscous solutions with a wide range of viscosities up to 7.0 Pa.s.
- They are highly suitable for making dispersion containing 60% solids.
- Turbines are suitable for liquids of large volume and high viscosity with the additional provision of baffles in the tank.
- As they generate high radial flow efficiency of mixing is high.
- In low viscous materials of large volumes, the turbine creates a strong current that spread throughout the tank destroying stagnant pockets.
Disadvantages of Turbine Mixer
- They are not preferred for solvents with high viscosity such as more than 20 cP.
- There is the possibility of air entrapment that may cause the oxidation of material being mixed.
Applications of Turbine Mixer
- Highly used in chemical reactions and extraction operations. For example, liquid and gas reactions.
- Used in preparing emulsions, suspensions, and syrups.
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