Industrial Mixing Basics: Square Tanks vs Round Tanks for Solid Suspension

The Chemical Industry Typically Uses Round Tanks to Suspend Solids in Liquid but Other Industries Often Prefer Square Tanks

Agitation to suspend solids in a liquid is a primary consideration in the chemical industry.  The most common configuration for solid suspension utilizes agitators designed for fully baffled, round tanks.  There are some industries and applications where use of square tanks is desired.

This In The Mix Blog reviews the mixing characteristics in a square tank in comparison to a round tank.  Videos are provided to demonstrate agitation to suspend solids in a liquid for both round and square tanks.


Solid Suspension in Baffled Round Tank

For solid suspension in a liquid, axial flow impellers are commonly used in fully baffled cylindrical tank.  This configuration provides top to bottom flow patterns for suspension of the solids.  The following video demonstrates solid suspension under these conditions.  A ProQuip HiFlow high efficiency axial flow impeller is used in a fully baffled round tank filled with water.  Impeller diameter and spacing are typical for the lab tank diameter and liquid level used in the video.  Colored beads, with a specific gravity slightly more than water, are used to demonstrate solid suspension and to help visualize the top to bottom liquid flow pattern.  As shown, this configuration provides complete solid suspension.

Solid Suspension in Unbaffled Round Tank

In comparison, using a center-mounted mixer in a unbaffled round tank with axial flow impellers, under the same conditions as the baffled tank, provides very little top to bottom flow.  The video below demonstrates the primary flow pattern that develops in the unbaffled round tank is rotating horizontally (radial) with development of a center vortex.  The solids remain primarily on the bottom of the tank.

Solid Suspension in an Unbaffled Square Tank 

The last video demonstrates the flow pattern for a ProQuip HiFlow high efficiency axial flow impeller in a unbaffled square tank. Unlike the unbaffled round tank, the square corners for this tank provide a similar effect to the liquid flow pattern as do baffles in a round tank.  A ProQuip HiFlow high efficiency axial flow impeller is used in a unbaffled square tank filled with water.  The tank diameter (side dimension), impeller diameter and spacing matches what was used in the round tank video.  Good top to bottom flow pattern is developed to aid in the suspension of the solids. Additionally, the impeller power number (Np) is comparable to the fully baffled, round tank.

For More Information

ProQuip tank agitators are used for solid suspension in chemical production and a wide variety of other industries. For more information on ProQuip mixing solutions for your application, email or call us at 330-468-1850.