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
Off 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.
09.21.23