Pitched Blade Turbine

PITCHED BLADE TURBINE

Introduction

-Pitched Blade Turbine Impeller is essentially a modified open flat blade turbine with the blades angled.

-Available with different number of blades, blade widths and different blade angles, the 4-blade, 45″ pitch is the most popular. It is a good compromise between high pumping efficiency and high shear for processes that require both
centipoises.

-The axial flow turbine is significantly more efficient than the Flat Blade Radial Turbine Impeller in terms of flow per horsepower.

History

-Concerning Pitched Blade Turbine, even though are commonly employed in industrial mixing applications, a smaller number of such exhaustive works can be found in the literature.

-Most workers focused their attention on mean and R.M.S. Velocities in the bulk of the vessel and around the impeller (Hockey & Nouri, 1996; Kresta & Wood, 1993; Javorsky et al. 1991).

-Tatterson et al. (1980) observed the trailing vortices generated by a 45° 6-blade PBT in a vessel of diameter T = 295 mm, and a 45° 4-blade PBT in a 914 mm vessel. They found that the vertical structure of the 6-blade was not as well
defined as for the 4-blade. Schaefer et al. (1998) studied a 45° 4-blade PBT in a 152 mm diameter tank with clearance C= T/3.

-They found that the single vortex generated from behind a blade had an axis inclined at 20° to the horizontal and that its radius was essentially constant. All the works previous mentioned, due to their measurement systems, focused
their attention on the zone between to subsequent blades, i.e. 60° for a 6-blade (Rushton). Nothing has been studied about the behavior of the vortices after have passed the incoming blade.

Different Types of Pitched Blade turbines

An extremely efficient turbulent flow impeller for blending, heat transfer and solids suspension. Most effective for Reynolds numbers over 50. Developed to minimize the creation of trailing vortices and incorporating the otherwise
wasted energy into macro-flow.

-An established industry standard for axial flow impellers

-Extremely efficient: creates greater fluid motion with less energy

-Ideal for blending, heat transfer and solids suspension

A reasonably cost effective impeller in both turbulent and laminar flow. Good impeller for applications where the viscosity changes over a wide range causing the flow regime to vary between turbulent and laminar flow. A reasonably cost effective impeller for solids suspension.

S-4 or Straight Blade Impeller

It is a cost effective impeller for operation very near the floor of a tank for agitating the heel in solids suspension applications. It is also an effective impeller in laminar flow applications, especially when impeller Reynolds numbers
drop below 50.

-Close clearance design for operation near the tank bottom -Excellent for low-liquid-level solids suspension applications

-Designed for use in laminar regime (Reynolds number < 50) applications

Application Miscible Fluids Suspension Fluids Immiscible FluidsBlending
Impeller High Efficiency
(HE-3, SC-3)
High Efficiency
(HE-3, SC-3, Maxflo W)
ChemShear,
Dispersion, P-4

 Application Construction & Power Calculation

The PBT is a generic impeller design. It is a 4-bladed turbine with 45° pitched blades. Blade width is 0.2 times its swept diameter. The PBT has long been considered an axial flow impeller. That really depends on its D/T. For small D/T, the PBT is an axial flow impeller. For very large D/T, the PBT is almost a radial flow impeller. A 3-bladed PBT with 30° pitched blades is almost as axial as a hydrofoil. In Europe, the 6-bladed version of the PBT is more common.

1) The Pitched Blade Turbine is more flow efficient than the radial style impellers and produces more fluid shear than the hydrofoil impellers.
2) The impeller of choice when both flow velocity and fluid shear is required and/or when very high mixing intensity
is required when the use of a hydrofoil would result in too high a tip speed or operating speed.

3) Most common configuration is 4 blades pitched at 45° with the most common types being either 3 or 4 blades pitched at 32°.

4) The 32° variety can handle slightly higher viscosity and is useful in low level mixing operations.

5) This style of impeller is the least expensive axial flow impeller Turbulent Power Number Np=1.27, Flow Number Nq=0.79.

Re Np Nq theta N discharge angle Notes
1       90 deg T = 17.5″

Z = 12.0″,   Z/T = 0.69

D = 6.0″,    D/T = 0.34

OB = 3.0″,  OB/D = 0.5

4 baffles

Fluids:  96% Glycerin and Carbopol

10     10000 90
30     1300 80
100     400 75
300     65 50
1000     17 45
3000       45
10000       45
turbulent 1.26 0.79   45

Application

-This agitator use in for very high velocity mixing require

-It is also use to blending the liquids, blending the polymer.

-In case of reactor for homogeneity maintain in reactor to reaction occur uniformly this is widely use.

-This is also use for low to medium viscous liquid.

-It is also use for suspension of solid particles in liquid. -Recommended for higher

-Viscosity applications requiring high flow in the transitional flow regime

-Reduces blend time by half

-Shear rates are modest for both high and low viscosity conditions

-Fluid foil design delivers better axial motion and reduces power consumption

Comparison

For high viscosity liquid generate the shear six blade compare to four blade is widely used.

-In case of very high viscosity this may not use.

-Compare to four-blade pitch turbine power consumption is higher.

-Suspension formation more than four pitched blade turbine.

-Compare to axial flow impeller shear current generate at a very high rate.

-Very low volume pocket are not agitated compare to axial flow impeller.

Limitation

-Very high power required so power consumption more.

-In case of very high viscosity chances to brake the blade.

-In case of six-pitched blade turbine the area of material is more also surface area is more so corrosion as well as erosion problem high because of high velocity.

-For very high viscosity it is not use.

-For the mixers in which the mixing time is more it is not used.

-For low density soft material it is not use otherwise may decomposition occurs.

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