Tank Baffles

Tank Baffles for Industrial Mixing

Tank baffle design

As the power input of a mixer increases, the liquid tends to swirl around the tank and, at high intensity, can even form a vortex above the impeller. This is a sign of poor mixing: the bulk liquid simply rotates with the impeller, so there is very little exchange between the different zones of the tank.

Baffles break up this swirling motion and promote top-to-bottom circulation, so that the whole volume of liquid passes through the high-turbulence zone created by the impeller.
More energy is transferred into the liquid, which shortens the mixing time needed to reach the required homogeneity.

Baffles are normally recommended in cylindrical tanks, unless the viscosity is very high or the mixing intensity very low. If baffles cannot be fitted, the mixer can be mounted off-centre or at an angle – our application engineers will be happy to advise you.

In rectangular tanks, the corners act as natural baffles, so baffles are generally not needed unless vigorous agitation is required. This guide therefore focuses mainly on cylindrical tanks.

Baffle Design

The standard configuration uses 3 or 4 equally spaced vertical baffles with a width of T/12, where T is the inside diameter of the tank. Making the baffles larger or adding more does not improve mixing. Baffles are usually mounted with a small gap from the tank wall, which lets liquid flow behind them and prevents dead zones. The recommended wall clearance depends on the baffle width (typically W/5). This standard design suits general mixing of water-like liquids, but other process factors can change the optimum baffle design.

W/T vs. Viscosity Plot
W/T Baffle width ratio W/T versus viscosity chart
Viscosity (cP)

Effect of Viscosity on Baffle Design

With more viscous liquids, baffles can be made narrower while still mixing effectively. The relationship between viscosity and the required baffle width is shown in the chart.

This relationship is only a guideline: for very viscous liquids in small vessels, it can give baffles and wall clearances that are too narrow.

Other Considerations


In solids suspension, solids can settle in dead zones at the foot of the baffles and be hard to resuspend. In flat-bottomed tanks, a gap is therefore left between the bottom of the baffles and the tank floor.

This gap is generally sized so that some turbulence from the impeller reaches the tank floor, keeping particles moving and in suspension at all times.

To draw down a light or hard-to-wet powder, the baffles should stop below the liquid surface. Combined with an impeller positioned one to two impeller diameters below the surface, this creates a small vortex in the upper part of the tank that quickly pulls the powder into the liquid. The gap between the top of the baffles and the liquid surface is generally 300 mm.

Tank baffle dimensions diagram

T – Inside diameter of the tank
W – Baffle width
C – Baffle-to-wall clearance
B – Baffle-to-bottom clearance

Baffle Thickness

The minimum baffle thickness can be calculated from the fluid forces acting on the baffle and the allowable bending stress of its material. The method below assumes that the baffles must absorb the full force generated by the mixer torque.


Latex formula

τ – Mixer torque (Nm)
P – Motor power (kW)
n – Mixer speed (rpm)

The torque is converted into a force on the baffles and divided by the number of baffles. The adjustment factor (Af) accounts for the distribution of force along the baffle; for a conservative design it can be set to 1, assuming all the force from the mixer acts at a single point.


Latex formula FB – Force on each baffle (N)
Af – Adjustment factor (set to 1 for a conservative design)
NB – Number of baffles
T – Tank diameter (mm)
Bw – Baffle width (mm)
Bc – Baffle-to-wall clearance (mm)

From this value, the baffle thickness is calculated using the allowable bending stress of the material and the mounting arrangement, assuming the force acts midway between two baffle brackets.

Latex formula

Bt – Baffle thickness (mm)
L – Distance between baffle brackets (mm)
S – Allowable bending stress (N/mm²) (34 N/mm² for steel)

Non-cylindrical tanks

Non-cylindrical mixing tanks are usually rectangular or horizontal. As noted above, they generally do not need baffles unless strong agitation is required: being asymmetrical around the mixer shaft, they are self-baffling when the mixer power input is below 165 W/m³.

Rectangular Tanks

Horizontal tanks

If baffles are required in a rectangular tank, they can be fitted as shown below. For roughly square tanks, the layout is similar to a cylindrical tank.

In horizontal tanks, baffles can be mounted on the tank centreline as shown below. They are generally not fitted on the curved sides, because they are hard to install there and need enough clearance from the impeller.
Baffles in a square tank Baffles in a horizontal tank

In longer tanks, only the baffles closest to the impeller are needed, as their effect decreases with distance from the impeller.

In longer tanks, the baffles are set further from the tank ends to leave about 600 mm of clearance from the impeller.
Baffles in a rectangular tank
Baffles in a horizontal tank

For even longer tanks, several mixers are generally recommended, with baffles next to each mixer.

When several mixers are used, baffles must be fitted for each mixer. They are generally positioned as shown below, with a uniform 600 mm clearance, along the full length of the tank.
Baffles in a rectangular tank Baffles in a horizontal tank

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