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Anti-Swirl Baffling, Vertical Tank Configuration:

ANTI-SWIRL TANK BAFFLING
Applying the 80/20 rule, most fluids fall under the classification of water-like viscosity where either proper Anti-Swirl Tank Baffling is required or an angular offset mounting arrangement is applied instead of using anti-swirl baffles.  These configurations are not only important to ensure satisfactory mixing results, they are also required to protect the mixer from premature failure as most mixers are designed under a No Swirl fluid regime.  The exact fluid regime that your mixer is designed for should be indicated our that mixers outline and installation drawing, which depicts the overall design of the mixer.   

Anti-Swirl Tank Baffles ensure good mixing by redirecting the angular component of mixing, also known as swirl or vortexing, into the preferred vertical and radial components of mixing.  On the other hand, an over baffled configuration, normally associated with higher viscosity applications, will localize the mixing action and will reduce the overall mass flow such that the mixing in certain regions of the mix tank will be unsatisfactory.  As such, it is always best to secure an Anti-Swirl Baffle recommendation from your mixer supplier.  To protect your equipment premature failure and to ensure your mixers  longevity, monitoring the resulting flow patterns is recommended, as modifications to this initial recommendations for the anti-swirl baffles or mounting orientation may be required 4   

ANTI-SWIRL BAFFLE CONFIGURATION: STANDARD CONDITIONS:
The term “standard (width) baffles”, actually refers to a standard tank & fluid conditions.  Vertical cylindrical tanks with water like viscosities where the mixer is mounted on-the-tanks-centerline will require standard baffles.  Standard baffles are defined as follows:

Baffle Width = 1/12th  Tank Diameter
Baffle Off Wall Distance = 1/6th  to 1/12th  Baffle Width
Baffle Length = Full Straight Side1,2,3
O
ff Bottom = 1/8th  to 1/16th  x (tank straight side)

NOTES:
1)
Three bladed impellers such as hydrofoils and propellers typically require three (3) anti-swirl tank baffles, oriented 120 degree apart.  All other impellers that typically have either a higher radial discharge component or that transform a great degree of the available horsepower into fluid shear require four (4) anti-swirl tank baffles, oriented 90 degrees apart.  On ASME or 2:1 semi-elliptical Dish (heads) top & bottoms, baffles usually begin & end where the dish & straight wall meet.  Physically taller dishes and unique mixing applications may require special dish baffling. 
2)
To promote additional surface motion for the additions at the surface, anti-swirl baffles of 80 to 85% of the straight side can be used, leaving the upper region of the tank unbaffled.
3)
On flat bottom tanks, locating the baffle approximately 1/8th  to 1/16th  of the tank straight side off the tank bottom is acceptable to prevent potential hang-up points on the bottom where the baffle meet the tank bottom.
4) Dependent upon the tank configuration, and numerous other parameters, swirl and vortexing may result after installation as recommended by your mixer manufacturer.  For example, swirl and vortexing resulting in a cylindrical tank where an angular offset mounting arrangement was used in combination with a tall cone bottom tank.  The cone influenced the resulting swirl condition, where the installation of a tank anti-swirl baffle was required to stem the radial flow pattern.     

04.12.11 

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