INDOFAB Recommends V paddle Designs of Flocculator
Comparison Based on the old academic references, > 100+ installations and Basic Fluid Mechanics :
Flocculators with Flat paddles absorb larger power & stress due to higher drag.
The fact can be explained with appropriate reasoning as below :
Flat paddles tend to directly displace the liquid in path in perpendicular direction and hence face higher drag/deflection force.
This causes requirement of higher power to drag the paddles. .
Design Paddle area = Paddle Face area
There is no difference between effective area and actual flat area.
Unlike V shaped paddles which have more contact area per unit of projected area, consuming less power.
During Rotation As the Flat paddle contacts the Liquid/flocs. And pushes them in Perpendicular direction, the liquid/flocs, impend in one direction and quickly loose the inertia required for motion due to liquid resistance.
Hence zone of influence is very limited & liquid/flocs are directly impacted
In-spite of high power consumption, the Influence zone in Flat paddles is very less and the laminar flow pattern created does not last over large area, it quickly diminishes. The case in V paddles is exactly opposite, they have larger influence area with same power consumption.
Flat paddles due to higher drag, tend to deflect, bend and at times induce deflection in shaft.
As they are prone to drag/deflection due to direct flat blade contact, they are required to be of higher thickness inducing higher stress in shaft, bearings, gear drive inturn consuming more power for the same work done.
Higher thicknesses of Flat paddle increase dead load, shaft size, gear box size and inturn is very bulky assembly causing more dead load on mechanism bridge.
V paddles are Hydrodynamic in Design, light weight hence more paddles can easily be accommodated to give higher flocculation area of blades, and have lesser impact & stress all components of the flocculators like drive, shaft, gear box etc
The Flat Paddle only provides Beating action in perpendicular direction, pushing all the liquid in one direction at the same level.
The V paddles provide action like Pitch Blade turbine and hence mixing and simultaneous pumping is achieved. At slow speed this gives a multi-directional laminar flow due to pumping action.
Refer below Academic Proven References Graphs and Power number with Formula used for determining power.
Power Number chart below clearly show Flat Blade power number is Higher for all Levels of Mixing. Ref Line no. 1 as compared to Pitched Blade Turbine . Ref.Line no.2 For our application of Flocculation Reynolds number should be in Laminar Zone means 102 to 103 The difference is power number can be clearly seen.
Based on the above V blades are designed with surfaces of 45deg. Blades
i.e, Pitch Blade Turbine.
Academic Example from same book is depicted below :
Clearly shows Flat Bladed Disc vs. Pitched Blade Power consumed for same application :